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[10/51] [partial] qpid-site git commit: QPID-7584: update site for
qpid-cpp 1.36.0
http://git-wip-us.apache.org/repos/asf/qpid-site/blob/54b18507/input/releases/qpid-cpp-1.36.0/cpp-broker/book/chapter-Managing-CPP-Broker.html.in
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+<div class="docbook"><div class="navheader"><table summary="Navigation header" width="100%"><tr><th align="center" colspan="3">Chapter 2. 
+ Managing the AMQP Messaging Broker
+ </th></tr><tr><td align="left" width="20%"><a accesskey="p" href="ha-queue-replication.html">Prev</a> </td><th align="center" width="60%"> </th><td align="right" width="20%"> <a accesskey="n" href="ch02s02.html">Next</a></td></tr></table><hr /></div><div class="chapter"><div class="titlepage"><div><div><h1 class="title"><a id="chapter-Managing-CPP-Broker"></a>Chapter 2. 
+ Managing the AMQP Messaging Broker
+ </h1></div></div></div><div class="toc"><p><strong>Table of Contents</strong></p><dl class="toc"><dt><span class="section"><a href="chapter-Managing-CPP-Broker.html#section-Managing-CPP-Broker">2.1. Managing the C++ Broker </a></span></dt><dd><dl><dt><span class="section"><a href="chapter-Managing-CPP-Broker.html#MgmtC-2B-2B-Usingqpidconfig">2.1.1.
+ Using qpid-config
+ </a></span></dt><dt><span class="section"><a href="chapter-Managing-CPP-Broker.html#MgmtC-2B-2B-Usingqpidroute">2.1.2.
+ Using qpid-route
+ </a></span></dt><dt><span class="section"><a href="chapter-Managing-CPP-Broker.html#MgmtC-2B-2B-Usingqpidtool">2.1.3.
+ Using qpid-tool
+ </a></span></dt><dt><span class="section"><a href="chapter-Managing-CPP-Broker.html#MgmtC-2B-2B-Usingqpidprintevents">2.1.4.
+ Using
+ qpid-printevents
+ </a></span></dt><dt><span class="section"><a href="chapter-Managing-CPP-Broker.html#idm221083450544">2.1.5. Using qpid-ha</a></span></dt></dl></dd><dt><span class="section"><a href="ch02s02.html">2.2.
+ Qpid Management Framework
+ </a></span></dt><dd><dl><dt><span class="section"><a href="ch02s02.html#QpidManagementFramework-WhatIsQMF">2.2.1.
+ What Is QMF
+ </a></span></dt><dt><span class="section"><a href="ch02s02.html#QpidManagementFramework-GettingStartedwithQMF">2.2.2.
+ Getting
+ Started with QMF
+ </a></span></dt><dt><span class="section"><a href="ch02s02.html#QpidManagementFramework-QMFConcepts">2.2.3.
+ QMF Concepts
+ </a></span></dt><dt><span class="section"><a href="ch02s02.html#QpidManagementFramework-TheQMFProtocol">2.2.4.
+ The QMF
+ Protocol
+ </a></span></dt><dt><span class="section"><a href="ch02s02.html#QpidManagementFramework-HowtoWriteaQMFConsole">2.2.5.
+ How
+ to Write a QMF Console
+ </a></span></dt><dt><span class="section"><a href="ch02s02.html#QpidManagementFramework-HowtoWriteaQMFAgent">2.2.6.
+ How to
+ Write a QMF Agent
+ </a></span></dt></dl></dd><dt><span class="section"><a href="ch02s03.html">2.3.
+ QMF Python Console Tutorial
+ </a></span></dt><dd><dl><dt><span class="section"><a href="ch02s03.html#QMFPythonConsoleTutorial-PrerequisiteInstallQpidMessaging">2.3.1.
+ Prerequisite
+ - Install Qpid Messaging
+ </a></span></dt><dt><span class="section"><a href="ch02s03.html#QMFPythonConsoleTutorial-SynchronousConsoleOperations">2.3.2.
+ Synchronous
+ Console Operations
+ </a></span></dt><dt><span class="section"><a href="ch02s03.html#QMFPythonConsoleTutorial-AsynchronousConsoleOperations">2.3.3.
+ Asynchronous
+ Console Operations
+ </a></span></dt><dt><span class="section"><a href="ch02s03.html#QMFPythonConsoleTutorial-DiscoveringwhatKindsofObjectsareAvailable">2.3.4.
+ Discovering what Kinds of Objects are Available
+ </a></span></dt></dl></dd></dl></div><div class="section"><div class="titlepage"><div><div><h2 class="title"><a id="section-Managing-CPP-Broker"></a>2.1.  Managing the C++ Broker </h2></div></div></div><p>
+ There are quite a few ways to interact with the C++ broker. The
+ command line tools
+ include:
+ </p><div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem"><p>qpid-route - used to configure federation (a set of federated
+ brokers)
+ </p></li><li class="listitem"><p>qpid-config - used to configure queues, exchanges, bindings
+ and list them etc
+ </p></li><li class="listitem"><p>qpid-tool - used to view management information/statistics
+ and call any management actions on the broker
+ </p></li><li class="listitem"><p>qpid-printevents - used to receive and print QMF events
+ </p></li><li class="listitem"><p>qpid-ha - used to interact with the High Availability module
+ </p></li></ul></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a id="MgmtC-2B-2B-Usingqpidconfig"></a>2.1.1. 
+ Using qpid-config
+ </h3></div></div></div><p>
+ This utility can be used to create queues exchanges and bindings,
+ both durable and transient. Always check for latest options by
+ running --help command.
+ </p><pre class="programlisting">
+$ qpid-config --help
+Usage: qpid-config [OPTIONS]
+ qpid-config [OPTIONS] exchanges [filter-string]
+ qpid-config [OPTIONS] queues [filter-string]
+ qpid-config [OPTIONS] add exchange <type> <name> [AddExchangeOptions]
+ qpid-config [OPTIONS] del exchange <name>
+ qpid-config [OPTIONS] add queue <name> [AddQueueOptions]
+ qpid-config [OPTIONS] del queue <name>
+ qpid-config [OPTIONS] bind <exchange-name> <queue-name> [binding-key]
+ qpid-config [OPTIONS] unbind <exchange-name> <queue-name> [binding-key]
+
+Options:
+ -b [ --bindings ] Show bindings in queue or exchange list
+ -a [ --broker-addr ] Address (localhost) Address of qpidd broker
+ broker-addr is in the form: [username/password@] hostname | ip-address [:<port>]
+ ex: localhost, 10.1.1.7:10000, broker-host:10000, guest/guest@localhost
+
+Add Queue Options:
+ --durable Queue is durable
+ --file-count N (8) Number of files in queue's persistence journal
+ --file-size N (24) File size in pages (64Kib/page)
+ --max-queue-size N Maximum in-memory queue size as bytes
+ --max-queue-count N Maximum in-memory queue size as a number of messages
+ --limit-policy [none | reject | flow-to-disk | ring | ring-strict]
+ Action taken when queue limit is reached:
+ none (default) - Use broker's default policy
+ reject - Reject enqueued messages
+ flow-to-disk - Page messages to disk
+ ring - Replace oldest unacquired message with new
+ ring-strict - Replace oldest message, reject if oldest is acquired
+ --order [fifo | lvq | lvq-no-browse]
+ Set queue ordering policy:
+ fifo (default) - First in, first out
+ lvq - Last Value Queue ordering, allows queue browsing
+ lvq-no-browse - Last Value Queue ordering, browsing clients may lose data
+
+Add Exchange Options:
+ --durable Exchange is durable
+ --sequence Exchange will insert a 'qpid.msg_sequence' field in the message header
+ with a value that increments for each message forwarded.
+ --ive Exchange will behave as an 'initial-value-exchange', keeping a reference
+ to the last message forwarded and enqueuing that message to newly bound
+ queues.
+</pre><p>
+ Get the summary page
+ </p><pre class="programlisting">
+$ qpid-config
+Total Exchanges: 6
+ topic: 2
+ headers: 1
+ fanout: 1
+ direct: 2
+ Total Queues: 7
+ durable: 0
+ non-durable: 7
+</pre><p>
+ List the queues
+ </p><pre class="programlisting">
+$ qpid-config queues
+Queue Name Attributes
+=================================================================
+pub_start
+pub_done
+sub_ready
+sub_done
+perftest0 --durable
+reply-dhcp-100-18-254.bos.redhat.com.20713 auto-del excl
+topic-dhcp-100-18-254.bos.redhat.com.20713 auto-del excl
+
+</pre><p>
+ List the exchanges with bindings
+ </p><pre class="programlisting">
+$ ./qpid-config -b exchanges
+Exchange '' (direct)
+ bind pub_start => pub_start
+ bind pub_done => pub_done
+ bind sub_ready => sub_ready
+ bind sub_done => sub_done
+ bind perftest0 => perftest0
+ bind mgmt-3206ff16-fb29-4a30-82ea-e76f50dd7d15 => mgmt-3206ff16-fb29-4a30-82ea-e76f50dd7d15
+ bind repl-3206ff16-fb29-4a30-82ea-e76f50dd7d15 => repl-3206ff16-fb29-4a30-82ea-e76f50dd7d15
+Exchange 'amq.direct' (direct)
+ bind repl-3206ff16-fb29-4a30-82ea-e76f50dd7d15 => repl-3206ff16-fb29-4a30-82ea-e76f50dd7d15
+ bind repl-df06c7a6-4ce7-426a-9f66-da91a2a6a837 => repl-df06c7a6-4ce7-426a-9f66-da91a2a6a837
+ bind repl-c55915c2-2fda-43ee-9410-b1c1cbb3e4ae => repl-c55915c2-2fda-43ee-9410-b1c1cbb3e4ae
+Exchange 'amq.topic' (topic)
+Exchange 'amq.fanout' (fanout)
+Exchange 'amq.match' (headers)
+Exchange 'qpid.management' (topic)
+ bind mgmt.# => mgmt-3206ff16-fb29-4a30-82ea-e76f50dd7d15
+</pre></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a id="MgmtC-2B-2B-Usingqpidroute"></a>2.1.2. 
+ Using qpid-route
+ </h3></div></div></div><p>
+ This utility is to create federated networks of brokers, This
+ allows you for forward messages between brokers in a network.
+ Messages can be routed statically (using "qpid-route route add")
+ where the bindings that control message forwarding are supplied
+ in the route. Message routing can also be dynamic (using
+ "qpid-route dynamic add") where the messages are automatically
+ forwarded to clients based on their bindings to the local broker.
+ </p><pre class="programlisting">
+$ qpid-route
+Usage: qpid-route [OPTIONS] dynamic add <dest-broker> <src-broker> <exchange> [tag] [exclude-list]
+ qpid-route [OPTIONS] dynamic del <dest-broker> <src-broker> <exchange>
+
+ qpid-route [OPTIONS] route add <dest-broker> <src-broker> <exchange> <routing-key> [tag] [exclude-list]
+ qpid-route [OPTIONS] route del <dest-broker> <src-broker> <exchange> <routing-key>
+ qpid-route [OPTIONS] queue add <dest-broker> <src-broker> <exchange> <queue>
+ qpid-route [OPTIONS] queue del <dest-broker> <src-broker> <exchange> <queue>
+ qpid-route [OPTIONS] route list [<dest-broker>]
+ qpid-route [OPTIONS] route flush [<dest-broker>]
+ qpid-route [OPTIONS] route map [<broker>]
+
+ qpid-route [OPTIONS] link add <dest-broker> <src-broker>
+ qpid-route [OPTIONS] link del <dest-broker> <src-broker>
+ qpid-route [OPTIONS] link list [<dest-broker>]
+
+Options:
+ -v [ --verbose ] Verbose output
+ -q [ --quiet ] Quiet output, don't print duplicate warnings
+ -d [ --durable ] Added configuration shall be durable
+ -e [ --del-empty-link ] Delete link after deleting last route on the link
+ -s [ --src-local ] Make connection to source broker (push route)
+ -t <transport> [ --transport <transport>]
+ Specify transport to use for links, defaults to tcp
+
+ dest-broker and src-broker are in the form: [username/password@] hostname | ip-address [:<port>]
+ ex: localhost, 10.1.1.7:10000, broker-host:10000, guest/guest@localhost
+</pre><p>
+ A few examples:
+ </p><pre class="programlisting">
+qpid-route dynamic add host1 host2 fed.topic
+qpid-route dynamic add host2 host1 fed.topic
+
+qpid-route -v route add host1 host2 hub1.topic hub2.topic.stock.buy
+qpid-route -v route add host1 host2 hub1.topic hub2.topic.stock.sell
+qpid-route -v route add host1 host2 hub1.topic 'hub2.topic.stock.#'
+qpid-route -v route add host1 host2 hub1.topic 'hub2.#'
+qpid-route -v route add host1 host2 hub1.topic 'hub2.topic.#'
+qpid-route -v route add host1 host2 hub1.topic 'hub2.global.#'
+</pre><p>
+ The link map feature can be used to display the entire federated
+ network configuration by supplying a single broker as an entry
+ point:
+ </p><pre class="programlisting">
+$ qpid-route route map localhost:10001
+
+Finding Linked Brokers:
+ localhost:10001... Ok
+ localhost:10002... Ok
+ localhost:10003... Ok
+ localhost:10004... Ok
+ localhost:10005... Ok
+ localhost:10006... Ok
+ localhost:10007... Ok
+ localhost:10008... Ok
+
+Dynamic Routes:
+
+ Exchange fed.topic:
+ localhost:10002 <=> localhost:10001
+ localhost:10003 <=> localhost:10002
+ localhost:10004 <=> localhost:10002
+ localhost:10005 <=> localhost:10002
+ localhost:10006 <=> localhost:10005
+ localhost:10007 <=> localhost:10006
+ localhost:10008 <=> localhost:10006
+
+ Exchange fed.direct:
+ localhost:10002 => localhost:10001
+ localhost:10004 => localhost:10003
+ localhost:10003 => localhost:10002
+ localhost:10001 => localhost:10004
+
+Static Routes:
+
+ localhost:10003(ex=amq.direct) <= localhost:10005(ex=amq.direct) key=rkey
+ localhost:10003(ex=amq.direct) <= localhost:10005(ex=amq.direct) key=rkey2
+</pre></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a id="MgmtC-2B-2B-Usingqpidtool"></a>2.1.3. 
+ Using qpid-tool
+ </h3></div></div></div><p>
+ This utility provided a telnet style interface to be able to
+ view, list all stats and action
+ all the methods. Simple capture below. Best to just play with it
+ and mail the list if you have
+ questions or want features added.
+ </p><pre class="programlisting">
+qpid:
+qpid: help
+Management Tool for QPID
+Commands:
+ list - Print summary of existing objects by class
+ list <className> - Print list of objects of the specified class
+ list <className> all - Print contents of all objects of specified class
+ list <className> active - Print contents of all non-deleted objects of specified class
+ list <list-of-IDs> - Print contents of one or more objects (infer className)
+ list <className> <list-of-IDs> - Print contents of one or more objects
+ list is space-separated, ranges may be specified (i.e. 1004-1010)
+ call <ID> <methodName> <args> - Invoke a method on an object
+ schema - Print summary of object classes seen on the target
+ schema <className> - Print details of an object class
+ set time-format short - Select short timestamp format (default)
+ set time-format long - Select long timestamp format
+ quit or ^D - Exit the program
+qpid: list
+Management Object Types:
+ ObjectType Active Deleted
+ ================================
+ qpid.binding 21 0
+ qpid.broker 1 0
+ qpid.client 1 0
+ qpid.exchange 6 0
+ qpid.queue 13 0
+ qpid.session 4 0
+ qpid.system 1 0
+ qpid.vhost 1 0
+qpid: list qpid.system
+Objects of type qpid.system
+ ID Created Destroyed Index
+ ==================================
+ 1000 21:00:02 - host
+qpid: list 1000
+Object of type qpid.system: (last sample time: 21:26:02)
+ Type Element 1000
+ =======================================================
+ config sysId host
+ config osName Linux
+ config nodeName localhost.localdomain
+ config release 2.6.24.4-64.fc8
+ config version #1 SMP Sat Mar 29 09:15:49 EDT 2008
+ config machine x86_64
+qpid: schema queue
+Schema for class 'qpid.queue':
+ Element Type Unit Access Notes Description
+ ===================================================================================================================
+ vhostRef reference ReadCreate index
+ name short-string ReadCreate index
+ durable boolean ReadCreate
+ autoDelete boolean ReadCreate
+ exclusive boolean ReadCreate
+ arguments field-table ReadOnly Arguments supplied in queue.declare
+ storeRef reference ReadOnly Reference to persistent queue (if durable)
+ msgTotalEnqueues uint64 message Total messages enqueued
+ msgTotalDequeues uint64 message Total messages dequeued
+ msgTxnEnqueues uint64 message Transactional messages enqueued
+ msgTxnDequeues uint64 message Transactional messages dequeued
+ msgPersistEnqueues uint64 message Persistent messages enqueued
+ msgPersistDequeues uint64 message Persistent messages dequeued
+ msgDepth uint32 message Current size of queue in messages
+ msgDepthHigh uint32 message Current size of queue in messages (High)
+ msgDepthLow uint32 message Current size of queue in messages (Low)
+ byteTotalEnqueues uint64 octet Total messages enqueued
+ byteTotalDequeues uint64 octet Total messages dequeued
+ byteTxnEnqueues uint64 octet Transactional messages enqueued
+ byteTxnDequeues uint64 octet Transactional messages dequeued
+ bytePersistEnqueues uint64 octet Persistent messages enqueued
+ bytePersistDequeues uint64 octet Persistent messages dequeued
+ byteDepth uint32 octet Current size of queue in bytes
+ byteDepthHigh uint32 octet Current size of queue in bytes (High)
+ byteDepthLow uint32 octet Current size of queue in bytes (Low)
+ enqueueTxnStarts uint64 transaction Total enqueue transactions started
+ enqueueTxnCommits uint64 transaction Total enqueue transactions committed
+ enqueueTxnRejects uint64 transaction Total enqueue transactions rejected
+ enqueueTxnCount uint32 transaction Current pending enqueue transactions
+ enqueueTxnCountHigh uint32 transaction Current pending enqueue transactions (High)
+ enqueueTxnCountLow uint32 transaction Current pending enqueue transactions (Low)
+ dequeueTxnStarts uint64 transaction Total dequeue transactions started
+ dequeueTxnCommits uint64 transaction Total dequeue transactions committed
+ dequeueTxnRejects uint64 transaction Total dequeue transactions rejected
+ dequeueTxnCount uint32 transaction Current pending dequeue transactions
+ dequeueTxnCountHigh uint32 transaction Current pending dequeue transactions (High)
+ dequeueTxnCountLow uint32 transaction Current pending dequeue transactions (Low)
+ consumers uint32 consumer Current consumers on queue
+ consumersHigh uint32 consumer Current consumers on queue (High)
+ consumersLow uint32 consumer Current consumers on queue (Low)
+ bindings uint32 binding Current bindings
+ bindingsHigh uint32 binding Current bindings (High)
+ bindingsLow uint32 binding Current bindings (Low)
+ unackedMessages uint32 message Messages consumed but not yet acked
+ unackedMessagesHigh uint32 message Messages consumed but not yet acked (High)
+ unackedMessagesLow uint32 message Messages consumed but not yet acked (Low)
+ messageLatencySamples delta-time nanosecond Broker latency through this queue (Samples)
+ messageLatencyMin delta-time nanosecond Broker latency through this queue (Min)
+ messageLatencyMax delta-time nanosecond Broker latency through this queue (Max)
+ messageLatencyAverage delta-time nanosecond Broker latency through this queue (Average)
+Method 'purge' Discard all messages on queue
+qpid: list queue
+Objects of type qpid.queue
+ ID Created Destroyed Index
+ ===========================================================================
+ 1012 21:08:13 - 1002.pub_start
+ 1014 21:08:13 - 1002.pub_done
+ 1016 21:08:13 - 1002.sub_ready
+ 1018 21:08:13 - 1002.sub_done
+ 1020 21:08:13 - 1002.perftest0
+ 1038 21:09:08 - 1002.mgmt-3206ff16-fb29-4a30-82ea-e76f50dd7d15
+ 1040 21:09:08 - 1002.repl-3206ff16-fb29-4a30-82ea-e76f50dd7d15
+ 1046 21:09:32 - 1002.mgmt-df06c7a6-4ce7-426a-9f66-da91a2a6a837
+ 1048 21:09:32 - 1002.repl-df06c7a6-4ce7-426a-9f66-da91a2a6a837
+ 1054 21:10:01 - 1002.mgmt-c55915c2-2fda-43ee-9410-b1c1cbb3e4ae
+ 1056 21:10:01 - 1002.repl-c55915c2-2fda-43ee-9410-b1c1cbb3e4ae
+ 1063 21:26:00 - 1002.mgmt-8d621997-6356-48c3-acab-76a37081d0f3
+ 1065 21:26:00 - 1002.repl-8d621997-6356-48c3-acab-76a37081d0f3
+qpid: list 1020
+Object of type qpid.queue: (last sample time: 21:26:02)
+ Type Element 1020
+ ==========================================================================
+ config vhostRef 1002
+ config name perftest0
+ config durable False
+ config autoDelete False
+ config exclusive False
+ config arguments {'qpid.max_size': 0, 'qpid.max_count': 0}
+ config storeRef NULL
+ inst msgTotalEnqueues 500000 messages
+ inst msgTotalDequeues 500000
+ inst msgTxnEnqueues 0
+ inst msgTxnDequeues 0
+ inst msgPersistEnqueues 0
+ inst msgPersistDequeues 0
+ inst msgDepth 0
+ inst msgDepthHigh 0
+ inst msgDepthLow 0
+ inst byteTotalEnqueues 512000000 octets
+ inst byteTotalDequeues 512000000
+ inst byteTxnEnqueues 0
+ inst byteTxnDequeues 0
+ inst bytePersistEnqueues 0
+ inst bytePersistDequeues 0
+ inst byteDepth 0
+ inst byteDepthHigh 0
+ inst byteDepthLow 0
+ inst enqueueTxnStarts 0 transactions
+ inst enqueueTxnCommits 0
+ inst enqueueTxnRejects 0
+ inst enqueueTxnCount 0
+ inst enqueueTxnCountHigh 0
+ inst enqueueTxnCountLow 0
+ inst dequeueTxnStarts 0
+ inst dequeueTxnCommits 0
+ inst dequeueTxnRejects 0
+ inst dequeueTxnCount 0
+ inst dequeueTxnCountHigh 0
+ inst dequeueTxnCountLow 0
+ inst consumers 0 consumers
+ inst consumersHigh 0
+ inst consumersLow 0
+ inst bindings 1 binding
+ inst bindingsHigh 1
+ inst bindingsLow 1
+ inst unackedMessages 0 messages
+ inst unackedMessagesHigh 0
+ inst unackedMessagesLow 0
+ inst messageLatencySamples 0
+ inst messageLatencyMin 0
+ inst messageLatencyMax 0
+ inst messageLatencyAverage 0
+qpid:
+</pre></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a id="MgmtC-2B-2B-Usingqpidprintevents"></a>2.1.4. 
+ Using
+ qpid-printevents
+ </h3></div></div></div><p>
+ This utility connects to one or more brokers and collects events,
+ printing out a line per event.
+ </p><pre class="programlisting">
+$ qpid-printevents --help
+Usage: qpid-printevents [options] [broker-addr]...
+
+Collect and print events from one or more Qpid message brokers. If no broker-
+addr is supplied, qpid-printevents will connect to 'localhost:5672'. broker-
+addr is of the form: [username/password@] hostname | ip-address [:<port>] ex:
+localhost, 10.1.1.7:10000, broker-host:10000, guest/guest@localhost
+
+Options:
+ -h, --help show this help message and exit
+</pre><p>
+ You get the idea... have fun!
+ </p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a id="idm221083450544"></a>2.1.5. Using qpid-ha</h3></div></div></div><p>This utility lets you monitor and control the activity of the clustering behavior provided by the HA module.
+ </p><pre class="programlisting">
+
+qpid-ha --help
+usage: qpid-ha <command> [<arguments>]
+
+Commands are:
+
+ ready Test if a backup broker is ready.
+ query Print HA configuration settings.
+ set Set HA configuration settings.
+ promote Promote broker from backup to primary.
+ replicate Set up replication from <queue> on <remote-broker> to <queue> on the current broker.
+
+For help with a command type: qpid-ha <command> --help
+
+ </pre></div></div></div><div class="navfooter"><hr /><table summary="Navigation footer" width="100%"><tr><td align="left" width="40%"><a accesskey="p" href="ha-queue-replication.html">Prev</a> </td><td align="center" width="20%"> </td><td align="right" width="40%"> <a accesskey="n" href="ch02s02.html">Next</a></td></tr><tr><td align="left" valign="top" width="40%">1.13. Replicating Queues with the HA module </td><td align="center" width="20%"><a accesskey="h" href="index.html">Home</a></td><td align="right" valign="top" width="40%"> 2.2. 
+ Qpid Management Framework
+ </td></tr></table></div></div>
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+<div class="docbook"><div class="navheader"><table summary="Navigation header" width="100%"><tr><th align="center" colspan="3">1.12. Active-Passive Messaging Clusters</th></tr><tr><td align="left" width="20%"><a accesskey="p" href="Using-message-groups.html">Prev</a> </td><th align="center" width="60%">Chapter 1. 
+ Running the AMQP Messaging Broker
+ </th><td align="right" width="20%"> <a accesskey="n" href="ha-queue-replication.html">Next</a></td></tr></table><hr /></div><div class="section"><div class="titlepage"><div><div><h2 class="title"><a id="chapter-ha"></a>1.12. Active-Passive Messaging Clusters</h2></div></div></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a id="ha-overview"></a>1.12.1. Overview</h3></div></div></div><p>
+
+ The High Availability (HA) module provides
+ <em class="firstterm">active-passive</em>, <em class="firstterm">hot-standby</em>
+ messaging clusters to provide fault tolerant message delivery.
+ </p><p>
+ In an active-passive cluster only one broker, known as the
+ <em class="firstterm">primary</em>, is active and serving clients at a time. The other
+ brokers are standing by as <em class="firstterm">backups</em>. Changes on the primary
+ are replicated to all the backups so they are always up-to-date or "hot". Backup
+ brokers reject client connection attempts, to enforce the requirement that clients
+ only connect to the primary.
+ </p><p>
+ If the primary fails, one of the backups is promoted to take over as the new
+ primary. Clients fail-over to the new primary automatically. If there are multiple
+ backups, the other backups also fail-over to become backups of the new primary.
+ </p><p>
+ This approach relies on an external <em class="firstterm">cluster resource manager</em>
+ to detect failures, choose the new primary and handle network partitions. <a class="ulink" href="https://fedorahosted.org/cluster/wiki/RGManager" target="_top">rgmanager</a> is supported
+ initially, but others may be supported in the future.
+ </p><div class="section"><div class="titlepage"><div><div><h4 class="title"><a id="ha-at-least-once"></a>1.12.1.1. Avoiding message loss</h4></div></div></div><p>
+ In order to avoid message loss, the primary broker <span class="emphasis"><em>delays
+ acknowledgement</em></span> of messages received from clients until the
+ message has been replicated and acknowledged by all of the back-up
+ brokers, or has been consumed from the primary queue.
+ </p><p>
+ This ensures that all acknowledged messages are safe: they have either
+ been consumed or backed up to all backup brokers. Messages that are
+ consumed <span class="emphasis"><em>before</em></span> they are replicated do not need to
+ be replicated. This reduces the work load when replicating a queue with
+ active consumers.
+ </p><p>
+ Clients keep <span class="emphasis"><em>unacknowledged</em></span> messages in a buffer
+ <a class="footnote" href="#ftn.idm221086980816" id="idm221086980816"><sup class="footnote">[1]</sup></a>
+ until they are acknowledged by the primary. If the primary fails, clients will
+ fail-over to the new primary and <span class="emphasis"><em>re-send</em></span> all their
+ unacknowledged messages.
+ <a class="footnote" href="#ftn.idm221087556864" id="idm221087556864"><sup class="footnote">[2]</sup></a>
+ </p><p>
+ If the primary crashes, all the <span class="emphasis"><em>acknowledged</em></span>
+ messages will be available on the backup that takes over as the new
+ primary. The <span class="emphasis"><em>unacknowledged</em></span> messages will be
+ re-sent by the clients. Thus no messages are lost.
+ </p><p>
+ Note that this means it is possible for messages to be
+ <span class="emphasis"><em>duplicated</em></span>. In the event of a failure it is possible for a
+ message to received by the backup that becomes the new primary
+ <span class="emphasis"><em>and</em></span> re-sent by the client. The application must take steps
+ to identify and eliminate duplicates.
+ </p><p>
+ When a new primary is promoted after a fail-over it is initially in
+ "recovering" mode. In this mode, it delays acknowledgement of messages
+ on behalf of all the backups that were connected to the previous
+ primary. This protects those messages against a failure of the new
+ primary until the backups have a chance to connect and catch up.
+ </p><p>
+ Not all messages need to be replicated to the back-up brokers. If a
+ message is consumed and acknowledged by a regular client before it has
+ been replicated to a backup, then it doesn't need to be replicated.
+ </p><div class="variablelist"><a id="ha-broker-states"></a><p class="title"><strong>HA Broker States</strong></p><dl class="variablelist"><dt><span class="term">Stand-alone</span></dt><dd><p>
+ Broker is not part of a HA cluster.
+ </p></dd><dt><span class="term">Joining</span></dt><dd><p>
+ Newly started broker, not yet connected to any existing primary.
+ </p></dd><dt><span class="term">Catch-up</span></dt><dd><p>
+ A backup broker that is connected to the primary and downloading
+ existing state (queues, messages etc.)
+ </p></dd><dt><span class="term">Ready</span></dt><dd><p>
+ A backup broker that is fully caught-up and ready to take over as
+ primary.
+ </p></dd><dt><span class="term">Recovering</span></dt><dd><p>
+ Newly-promoted primary, waiting for backups to connect and catch up.
+ Clients can connect but they are stalled until the primary is active.
+ </p></dd><dt><span class="term">Active</span></dt><dd><p>
+ The active primary broker with all backups connected and caught-up.
+ </p></dd></dl></div></div><div class="section"><div class="titlepage"><div><div><h4 class="title"><a id="limitations"></a>1.12.1.2. Limitations</h4></div></div></div><p>
+ There are a some known limitations in the current implementation. These
+ will be fixed in future versions.
+ </p><div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem"><p>
+ Transactional changes to queue state are not replicated atomically. If
+ the primary crashes during a transaction, it is possible that the
+ backup could contain only part of the changes introduced by a
+ transaction.
+ </p></li><li class="listitem"><p>
+ Configuration changes (creating or deleting queues, exchanges and
+ bindings) are replicated asynchronously. Management tools used to
+ make changes will consider the change complete when it is complete
+ on the primary, it may not yet be replicated to all the backups.
+ </p></li><li class="listitem"><p>
+ Federation links <span class="emphasis"><em>to</em></span> the primary will fail over
+ correctly. Federated links <span class="emphasis"><em>from</em></span> the primary
+ will be lost in fail over, they will not be re-connected to the new
+ primary. It is possible to work around this by replacing the
+ <code class="literal">qpidd-primary</code> start up script with a script that
+ re-creates federation links when the primary is promoted.
+ </p></li></ul></div></div></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a id="ha-virtual-ip"></a>1.12.2. Virtual IP Addresses</h3></div></div></div><p>
+ Some resource managers (including <span class="command"><strong>rgmanager</strong></span>) support
+ <em class="firstterm">virtual IP addresses</em>. A virtual IP address is an IP
+ address that can be relocated to any of the nodes in a cluster. The
+ resource manager associates this address with the primary node in the
+ cluster, and relocates it to the new primary when there is a failure. This
+ simplifies configuration as you can publish a single IP address rather
+ than a list.
+ </p><p>
+ A virtual IP address can be used by clients to connect to the primary. The
+ following sections will explain how to configure virtual IP addresses for
+ clients or brokers.
+ </p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a id="ha-broker-config"></a>1.12.3. Configuring the Brokers</h3></div></div></div><p>
+ The broker must load the <code class="filename">ha</code> module, it is loaded by
+ default. The following broker options are available for the HA module.
+ </p><div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3><p>
+ Broker management is required for HA to operate, it is enabled by
+ default. The option <code class="literal">mgmt-enable</code> must not be set to
+ "no"
+ </p></div><div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3><p>
+ Incorrect security settings are a common cause of problems when
+ getting started, see <a class="xref" href="chapter-ha.html#ha-security" title="1.12.9. Security and Access Control.">Section 1.12.9, “Security and Access Control.”</a>.
+ </p></div><div class="table"><a id="ha-broker-options"></a><p class="title"><strong>Table 1.28. Broker Options for High Availability Messaging Cluster</strong></p><div class="table-contents"><table border="1" summary="Broker Options for High Availability Messaging Cluster"><colgroup><col align="left" class="c1" /><col align="left" class="c2" /></colgroup><thead><tr><th align="center" colspan="2">
+ Options for High Availability Messaging Cluster
+ </th></tr></thead><tbody><tr><td align="left">
+ <code class="literal">ha-cluster <em class="replaceable"><code>yes|no</code></em></code>
+ </td><td align="left">
+ Set to "yes" to have the broker join a cluster.
+ </td></tr><tr><td align="left">
+ <code class="literal">ha-queue-replication <em class="replaceable"><code>yes|no</code></em></code>
+ </td><td align="left">
+ Enable replication of specific queues without joining a cluster, see <a class="xref" href="ha-queue-replication.html" title="1.13. Replicating Queues with the HA module">Section 1.13, “Replicating Queues with the HA module”</a>.
+ </td></tr><tr><td align="left">
+ <code class="literal">ha-brokers-url <em class="replaceable"><code>URL</code></em></code>
+ </td><td align="left">
+ <p>
+ The URL
+ <a class="footnote" href="#ftn.ha-url-grammar" id="ha-url-grammar"><sup class="footnote">[a]</sup></a>
+ used by cluster brokers to connect to each other. The URL should
+ contain a comma separated list of the broker addresses, rather than a
+ virtual IP address.
+ </p>
+ </td></tr><tr><td align="left"><code class="literal">ha-public-url <em class="replaceable"><code>URL</code></em></code> </td><td align="left">
+ <p>
+ This option is only needed for backwards compatibility if you
+ have been using the <code class="literal">amq.failover</code> exchange.
+ This exchange is now obsolete, it is recommended to use a
+ virtual IP address instead.
+ </p>
+ <p>
+ If set, this URL is advertised by the
+ <code class="literal">amq.failover</code> exchange and overrides the
+ broker option <code class="literal">known-hosts-url</code>
+ </p>
+ </td></tr><tr><td align="left"><code class="literal">ha-replicate </code><em class="replaceable"><code>VALUE</code></em></td><td align="left">
+ <p>
+ Specifies whether queues and exchanges are replicated by default.
+ <em class="replaceable"><code>VALUE</code></em> is one of: <code class="literal">none</code>,
+ <code class="literal">configuration</code>, <code class="literal">all</code>.
+ For details see <a class="xref" href="chapter-ha.html#ha-replicate-values" title="1.12.7. Controlling replication of queues and exchanges">Section 1.12.7, “Controlling replication of queues and exchanges”</a>.
+ </p>
+ </td></tr><tr><td align="left">
+ <p><code class="literal">ha-username <em class="replaceable"><code>USER</code></em></code></p>
+ <p><code class="literal">ha-password <em class="replaceable"><code>PASS</code></em></code></p>
+ <p><code class="literal">ha-mechanism <em class="replaceable"><code>MECHANISM</code></em></code></p>
+ </td><td align="left">
+ Authentication settings used by HA brokers to connect to each other,
+ see <a class="xref" href="chapter-ha.html#ha-security" title="1.12.9. Security and Access Control.">Section 1.12.9, “Security and Access Control.”</a>
+ </td></tr><tr><td align="left"><code class="literal">ha-backup-timeout<em class="replaceable"><code>SECONDS</code></em></code>
+ <a class="footnote" href="#ftn.ha-seconds-spec" id="ha-seconds-spec"><sup class="footnote">[b]</sup></a>
+ </td><td align="left">
+ <p>
+ Maximum time that a recovering primary will wait for an expected
+ backup to connect and become ready.
+ </p>
+ </td></tr><tr><td align="left">
+ <code class="literal">link-maintenance-interval <em class="replaceable"><code>SECONDS</code></em></code>
+ <a class="footnoteref" href="chapter-ha.html#ftn.ha-seconds-spec"><sup class="footnoteref">[b]</sup></a>
+ </td><td align="left">
+ <p>
+ HA uses federation links to connect from backup to primary.
+ Backup brokers check the link to the primary on this interval
+ and re-connect if need be. Default 2 seconds. Set lower for
+ faster failover, e.g. 0.1 seconds. Setting too low will result
+ in excessive link-checking on the backups.
+ </p>
+ </td></tr><tr><td align="left">
+ <code class="literal">link-heartbeat-interval <em class="replaceable"><code>SECONDS</code></em></code>
+ <a class="footnoteref" href="chapter-ha.html#ftn.ha-seconds-spec"><sup class="footnoteref">[b]</sup></a>
+ </td><td align="left">
+ <p>
+ HA uses federation links to connect from backup to primary.
+ If no heart-beat is received for twice this interval the primary will consider that
+ backup dead (e.g. if backup is hung or partitioned.)
+ This interval is also used to time-out for broker status checks,
+ it may take up to this interval for rgmanager to detect a hung or partitioned broker.
+ Clients sending messages may be held up during this time.
+ Default 120 seconds: you will probably want to set this to a lower value e.g. 10.
+ If set too low rgmanager may consider a slow broker to have failed and kill it.
+ </p>
+ </td></tr></tbody><tbody class="footnotes"><tr><td colspan="2"><div class="footnote" id="ftn.ha-url-grammar"><p><a class="para" href="#ha-url-grammar"><sup class="para">[a] </sup></a>
+ The full format of the URL is given by this grammar:
+ </p><pre class="programlisting">
+url = ["amqp:"][ user ["/" password] "@" ] addr ("," addr)*
+addr = tcp_addr / rmda_addr / ssl_addr / ...
+tcp_addr = ["tcp:"] host [":" port]
+rdma_addr = "rdma:" host [":" port]
+ssl_addr = "ssl:" host [":" port]'
+ </pre><p>
+ </p></div><div class="footnote" id="ftn.ha-seconds-spec"><p><a class="para" href="#ha-seconds-spec"><sup class="para">[b] </sup></a>
+ Values specified as <em class="replaceable"><code>SECONDS</code></em> can be a
+ fraction of a second, e.g. "0.1" for a tenth of a second.
+ They can also have an explicit unit,
+ e.g. 10s (seconds), 10ms (milliseconds), 10us (microseconds), 10ns (nanoseconds)
+ </p></div></td></tr></tbody></table></div></div><br class="table-break" /><p>
+ To configure a HA cluster you must set at least <code class="literal">ha-cluster</code> and
+ <code class="literal">ha-brokers-url</code>.
+ </p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a id="ha-rm"></a>1.12.4. The Cluster Resource Manager</h3></div></div></div><p>
+ Broker fail-over is managed by a <em class="firstterm">cluster resource
+ manager</em>. An integration with <a class="ulink" href="https://fedorahosted.org/cluster/wiki/RGManager" target="_top">rgmanager</a> is
+ provided, but it is possible to integrate with other resource managers.
+ </p><p>
+ The resource manager is responsible for starting the <span class="command"><strong>qpidd</strong></span> broker
+ on each node in the cluster. The resource manager then <em class="firstterm">promotes</em>
+ one of the brokers to be the primary. The other brokers connect to the primary as
+ backups, using the URL provided in the <code class="literal">ha-brokers-url</code> configuration
+ option.
+ </p><p>
+ Once connected, the backup brokers synchronize their state with the
+ primary. When a backup is synchronized, or "hot", it is ready to take
+ over if the primary fails. Backup brokers continually receive updates
+ from the primary in order to stay synchronized.
+ </p><p>
+ If the primary fails, backup brokers go into fail-over mode. The resource
+ manager must detect the failure and promote one of the backups to be the
+ new primary. The other backups connect to the new primary and synchronize
+ their state with it.
+ </p><p>
+ The resource manager is also responsible for protecting the cluster from
+ <em class="firstterm">split-brain</em> conditions resulting from a network partition. A
+ network partition divide a cluster into two sub-groups which cannot see each other.
+ Usually a <em class="firstterm">quorum</em> voting algorithm is used that disables nodes
+ in the inquorate sub-group.
+ </p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a id="ha-rm-config"></a>1.12.5. Configuring with <span class="command"><strong>rgmanager</strong></span> as resource manager</h3></div></div></div><p>
+ This section assumes that you are already familiar with setting up and configuring
+ clustered services using <span class="command"><strong>cman</strong></span> and
+ <span class="command"><strong>rgmanager</strong></span>. It will show you how to configure an active-passive,
+ hot-standby <span class="command"><strong>qpidd</strong></span> HA cluster with <span class="command"><strong>rgmanager</strong></span>.
+ </p><div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3><p>
+ Once all components are installed it is important to take the following step:
+ </p><pre class="programlisting">
+chkconfig rgmanager on
+chkconfig cman on
+chkconfig qpidd <span class="emphasis"><em>off</em></span>
+ </pre><p>
+ </p><p>
+ The qpidd service must be <span class="emphasis"><em>off</em></span> in
+ <code class="literal">chkconfig</code> because <code class="literal">rgmanager</code> will
+ start and stop <code class="literal">qpidd</code>. If the normal system init
+ process also attempts to start and stop qpidd it can cause rgmanager to
+ lose track of qpidd processes. The symptom when this happens is that
+ <code class="literal">clustat</code> shows a <code class="literal">qpidd</code> service to
+ be stopped when in fact there is a <code class="literal">qpidd</code> process
+ running. The <code class="literal">qpidd</code> log will show errors like this:
+ </p><pre class="programlisting">
+critical Unexpected error: Daemon startup failed: Cannot lock /var/lib/qpidd/lock: Resource temporarily unavailable
+ </pre><p>
+ </p></div><p>
+ You must provide a <code class="literal">cluster.conf</code> file to configure
+ <span class="command"><strong>cman</strong></span> and <span class="command"><strong>rgmanager</strong></span>. Here is
+ an example <code class="literal">cluster.conf</code> file for a cluster of 3 nodes named
+ node1, node2 and node3. We will go through the configuration step-by-step.
+ </p><pre class="programlisting">
+
+<?xml version="1.0"?>
+<!--
+This is an example of a cluster.conf file to run qpidd HA under rgmanager.
+This example assumes a 3 node cluster, with nodes named node1, node2 and node3.
+
+NOTE: fencing is not shown, you must configure fencing appropriately for your cluster.
+-->
+
+<cluster name="qpid-test" config_version="18">
+ <!-- The cluster has 3 nodes. Each has a unique nodeid and one vote
+ for quorum. -->
+ <clusternodes>
+ <clusternode name="node1.example.com" nodeid="1"/>
+ <clusternode name="node2.example.com" nodeid="2"/>
+ <clusternode name="node3.example.com" nodeid="3"/>
+ </clusternodes>
+
+ <!-- Resouce Manager configuration. -->
+
+ status_poll_interval is the interval in seconds that the resource manager checks the status
+ of managed services. This affects how quickly the manager will detect failed services.
+ -->
+ <rm status_poll_interval="1">
+ <!--
+ There is a failoverdomain for each node containing just that node.
+ This lets us stipulate that the qpidd service should always run on each node.
+ -->
+ <failoverdomains>
+ <failoverdomain name="node1-domain" restricted="1">
+ <failoverdomainnode name="node1.example.com"/>
+ </failoverdomain>
+ <failoverdomain name="node2-domain" restricted="1">
+ <failoverdomainnode name="node2.example.com"/>
+ </failoverdomain>
+ <failoverdomain name="node3-domain" restricted="1">
+ <failoverdomainnode name="node3.example.com"/>
+ </failoverdomain>
+ </failoverdomains>
+
+ <resources>
+ <!-- This script starts a qpidd broker acting as a backup. -->
+ <script file="/etc/init.d/qpidd" name="qpidd"/>
+
+ <!-- This script promotes the qpidd broker on this node to primary. -->
+ <script file="/etc/init.d/qpidd-primary" name="qpidd-primary"/>
+
+ <!--
+ This is a virtual IP address for client traffic.
+ monitor_link="yes" means monitor the health of the NIC used for the VIP.
+ sleeptime="0" means don't delay when failing over the VIP to a new address.
+ -->
+ <ip address="20.0.20.200" monitor_link="yes" sleeptime="0"/>
+ </resources>
+
+ <!-- There is a qpidd service on each node, it should be restarted if it fails. -->
+ <service name="node1-qpidd-service" domain="node1-domain" recovery="restart">
+ <script ref="qpidd"/>
+ </service>
+ <service name="node2-qpidd-service" domain="node2-domain" recovery="restart">
+ <script ref="qpidd"/>
+ </service>
+ <service name="node3-qpidd-service" domain="node3-domain" recovery="restart">
+ <script ref="qpidd"/>
+ </service>
+
+ <!-- There should always be a single qpidd-primary service, it can run on any node. -->
+ <service name="qpidd-primary-service" autostart="1" exclusive="0" recovery="relocate">
+ <script ref="qpidd-primary"/>
+ <!-- The primary has the IP addresses for brokers and clients to connect. -->
+ <ip ref="20.0.20.200"/>
+ </service>
+ </rm>
+</cluster>
+
+ </pre><p>
+ There is a <code class="literal">failoverdomain</code> for each node containing just that
+ one node. This lets us stipulate that the qpidd service should always run on all
+ nodes.
+ </p><p>
+ The <code class="literal">resources</code> section defines the <span class="command"><strong>qpidd</strong></span>
+ script used to start the <span class="command"><strong>qpidd</strong></span> service. It also defines the
+ <span class="command"><strong>qpid-primary</strong></span> script which does not
+ actually start a new service, rather it promotes the existing
+ <span class="command"><strong>qpidd</strong></span> broker to primary status.
+ </p><p>
+ The <code class="literal">resources</code> section also defines a virtual IP
+ address for clients: <code class="literal">20.0.20.200</code>.
+ </p><p>
+ <code class="filename">qpidd.conf</code> should contain these lines:
+ </p><pre class="programlisting">
+ha-cluster=yes
+ha-brokers-url=20.0.20.1,20.0.20.2,20.0.20.3
+ </pre><p>
+ The brokers connect to each other directly via the addresses
+ listed in <span class="command"><strong>ha-brokers-url</strong></span>. Note the client and broker
+ addresses are on separate sub-nets, this is recommended but not required.
+ </p><p>
+ The <code class="literal">service</code> section defines 3 <code class="literal">qpidd</code>
+ services, one for each node. Each service is in a restricted fail-over
+ domain containing just that node, and has the <code class="literal">restart</code>
+ recovery policy. The effect of this is that rgmanager will run
+ <span class="command"><strong>qpidd</strong></span> on each node, restarting if it fails.
+ </p><p>
+ There is a single <code class="literal">qpidd-primary-service</code> using the
+ <span class="command"><strong>qpidd-primary</strong></span> script which is not restricted to a
+ domain and has the <code class="literal">relocate</code> recovery policy. This means
+ rgmanager will start <span class="command"><strong>qpidd-primary</strong></span> on one of the nodes
+ when the cluster starts and will relocate it to another node if the
+ original node fails. Running the <code class="literal">qpidd-primary</code> script
+ does not start a new broker process, it promotes the existing broker to
+ become the primary.
+ </p><div class="section"><div class="titlepage"><div><div><h4 class="title"><a id="ha-rm-shutdown-node"></a>1.12.5.1. Shutting down qpidd on a HA node</h4></div></div></div><p>
+ As explained above both the per-node <code class="literal">qpidd</code> service
+ and the re-locatable <code class="literal">qpidd-primary</code> service are
+ implemented by the same <code class="literal">qpidd</code> daemon.
+ </p><p>
+ As a result, stopping the <code class="literal">qpidd</code> service will not stop
+ a <code class="literal">qpidd</code> daemon that is acting as primary, and
+ stopping the <code class="literal">qpidd-primary</code> service will not stop a
+ <code class="literal">qpidd</code> process that is acting as backup.
+ </p><p>
+ To shut down a node that is acting as primary you need to shut down the
+ <code class="literal">qpidd</code> service <span class="emphasis"><em>and</em></span> relocate the
+ primary:
+ </p><p>
+ </p><pre class="programlisting">
+clusvcadm -d somenode-qpidd-service
+clusvcadm -r qpidd-primary-service
+ </pre><p>
+ </p><p>
+ This will shut down the <code class="literal">qpidd</code> daemon on that node and
+ prevent the primary service service from relocating back to the node
+ because the qpidd service is no longer running there.
+ </p></div></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a id="ha-broker-admin"></a>1.12.6. Broker Administration Tools</h3></div></div></div><p>
+ Normally, clients are not allowed to connect to a backup broker. However
+ management tools are allowed to connect to a backup brokers. If you use
+ these tools you <span class="emphasis"><em>must not</em></span> add or remove messages from
+ replicated queues, nor create or delete replicated queues or exchanges as
+ this will disrupt the replication process and may cause message loss.
+ </p><p>
+ <span class="command"><strong>qpid-ha</strong></span> allows you to view and change HA configuration settings.
+ </p><p>
+ The tools <span class="command"><strong>qpid-config</strong></span>, <span class="command"><strong>qpid-route</strong></span> and
+ <span class="command"><strong>qpid-stat</strong></span> will connect to a backup if you pass the flag <span class="command"><strong>ha-admin</strong></span> on the
+ command line.
+ </p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a id="ha-replicate-values"></a>1.12.7. Controlling replication of queues and exchanges</h3></div></div></div><p>
+ By default, queues and exchanges are not replicated automatically. You can change
+ the default behaviour by setting the <code class="literal">ha-replicate</code> configuration
+ option. It has one of the following values:
+ </p><div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem"><p>
+ <em class="firstterm">all</em>: Replicate everything automatically: queues,
+ exchanges, bindings and messages.
+ </p></li><li class="listitem"><p>
+ <em class="firstterm">configuration</em>: Replicate the existence of queues,
+ exchange and bindings but don't replicate messages.
+ </p></li><li class="listitem"><p>
+ <em class="firstterm">none</em>: Don't replicate anything, this is the default.
+ </p></li></ul></div><p>
+ </p><p>
+ You can over-ride the default for a particular queue or exchange by passing the
+ argument <code class="literal">qpid.replicate</code> when creating the queue or exchange. It
+ takes the same values as <code class="literal">ha-replicate</code>
+ </p><p>
+ Bindings are automatically replicated if the queue and exchange being bound both
+ have replication <code class="literal">all</code> or <code class="literal">configuration</code>, they
+ are not replicated otherwise.
+ </p><p>
+ You can create replicated queues and exchanges with the
+ <span class="command"><strong>qpid-config</strong></span> management tool like this:
+ </p><pre class="programlisting">
+qpid-config add queue myqueue --replicate all
+ </pre><p>
+ To create replicated queues and exchanges via the client API, add a
+ <code class="literal">node</code> entry to the address like this:
+ </p><pre class="programlisting">
+"myqueue;{create:always,node:{x-declare:{arguments:{'qpid.replicate':all}}}}"
+ </pre><p>
+ There are some built-in exchanges created automatically by the broker, these
+ exchanges are never replicated. The built-in exchanges are the default (nameless)
+ exchange, the AMQP standard exchanges (<code class="literal">amq.direct, amq.topic, amq.fanout</code> and
+ <code class="literal">amq.match</code>) and the management exchanges (<code class="literal">qpid.management, qmf.default.direct</code> and
+ <code class="literal">qmf.default.topic</code>)
+ </p><p>
+ Note that if you bind a replicated queue to one of these exchanges, the
+ binding will <span class="emphasis"><em>not</em></span> be replicated, so the queue will not
+ have the binding after a fail-over.
+ </p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a id="ha-failover"></a>1.12.8. Client Connection and Fail-over</h3></div></div></div><p>
+ Clients can only connect to the primary broker. Backup brokers reject any
+ connection attempt by a client. Clients rejected by a backup broker will
+ automatically fail-over until they connect to the primary.
+ </p><p>
+ Clients are configured with the URL for the cluster (details below for
+ each type of client). There are two possibilities
+ </p><div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem"><p>
+ The URL contains multiple addresses, one for each broker in the cluster.
+ </p></li><li class="listitem"><p>
+ The URL contains a single <em class="firstterm">virtual IP address</em>
+ that is assigned to the primary broker by the resource manager.
+ This is the recommended configuration.
+ </p></li></ul></div><p>
+ In the first case, clients will repeatedly re-try each address in the URL
+ until they successfully connect to the primary. In the second case the
+ resource manager will assign the virtual IP address to the primary broker,
+ so clients only need to re-try on a single address.
+ </p><p>
+ When the primary broker fails, clients re-try all known cluster addresses
+ until they connect to the new primary. The client re-sends any messages
+ that were previously sent but not acknowledged by the broker at the time
+ of the failure. Similarly messages that have been sent by the broker, but
+ not acknowledged by the client, are re-queued.
+ </p><p>
+ TCP can be slow to detect connection failures. A client can configure a
+ connection to use a <em class="firstterm">heartbeat</em> to detect connection
+ failure, and can specify a time interval for the heartbeat. If heartbeats
+ are in use, failures will be detected no later than twice the heartbeat
+ interval. The following sections explain how to enable heartbeat in each
+ client.
+ </p><p>
+ Note: the following sections explain how to configure clients with
+ multiple dresses, but if you are using a virtual IP address you only need
+ to configure that one address for clients, you don't need to list all the
+ addresses.
+ </p><p>
+ Suppose your cluster has 3 nodes: <code class="literal">node1</code>,
+ <code class="literal">node2</code> and <code class="literal">node3</code> all using the
+ default AMQP port, and you are not using a virtual IP address. To connect
+ a client you need to specify the address(es) and set the
+ <code class="literal">reconnect</code> property to <code class="literal">true</code>. The
+ following sub-sections show how to connect each type of client.
+ </p><div class="section"><div class="titlepage"><div><div><h4 class="title"><a id="ha-clients"></a>1.12.8.1. C++ clients</h4></div></div></div><p>
+ With the C++ client, you specify multiple cluster addresses in a single URL
+ <a class="footnote" href="#ftn.idm221084088000" id="idm221084088000"><sup class="footnote">[3]</sup></a>
+ You also need to specify the connection option
+ <code class="literal">reconnect</code> to be true. For example:
+ </p><pre class="programlisting">
+qpid::messaging::Connection c("node1,node2,node3","{reconnect:true}");
+ </pre><p>
+ Heartbeats are disabled by default. You can enable them by specifying a
+ heartbeat interval (in seconds) for the connection via the
+ <code class="literal">heartbeat</code> option. For example:
+ </p><pre class="programlisting">
+qpid::messaging::Connection c("node1,node2,node3","{reconnect:true,heartbeat:10}");
+ </pre></div><div class="section"><div class="titlepage"><div><div><h4 class="title"><a id="ha-python-client"></a>1.12.8.2. Python clients</h4></div></div></div><p>
+ With the python client, you specify <code class="literal">reconnect=True</code>
+ and a list of <em class="replaceable"><code>host:port</code></em> addresses as
+ <code class="literal">reconnect_urls</code> when calling
+ <code class="literal">Connection.establish</code> or
+ <code class="literal">Connection.open</code>
+ </p><pre class="programlisting">
+connection = qpid.messaging.Connection.establish("node1", reconnect=True, reconnect_urls=["node1", "node2", "node3"])
+ </pre><p>
+ Heartbeats are disabled by default. You can
+ enable them by specifying a heartbeat interval (in seconds) for the
+ connection via the 'heartbeat' option. For example:
+ </p><pre class="programlisting">
+connection = qpid.messaging.Connection.establish("node1", reconnect=True, reconnect_urls=["node1", "node2", "node3"], heartbeat=10)
+ </pre></div><div class="section"><div class="titlepage"><div><div><h4 class="title"><a id="ha-jms-client"></a>1.12.8.3. Java JMS Clients</h4></div></div></div><p>
+ In Java JMS clients, client fail-over is handled automatically if it is
+ enabled in the connection. You can configure a connection to use
+ fail-over using the <span class="command"><strong>failover</strong></span> property:
+ </p><pre class="screen">
+ connectionfactory.qpidConnectionfactory = amqp://guest:guest@clientid/test?brokerlist='tcp://localhost:5672'&failover='failover_exchange'
+ </pre><p>
+ This property can take three values:
+ </p><div class="variablelist"><p class="title"><strong>Fail-over Modes</strong></p><dl class="variablelist"><dt><span class="term">failover_exchange</span></dt><dd><p>
+ If the connection fails, fail over to any other broker in the cluster.
+ </p></dd><dt><span class="term">roundrobin</span></dt><dd><p>
+ If the connection fails, fail over to one of the brokers specified in the <span class="command"><strong>brokerlist</strong></span>.
+ </p></dd><dt><span class="term">singlebroker</span></dt><dd><p>
+ Fail-over is not supported; the connection is to a single broker only.
+ </p></dd></dl></div><p>
+ In a Connection URL, heartbeat is set using the <span class="command"><strong>heartbeat</strong></span> property, which is an integer corresponding to the heartbeat period in seconds. For instance, the following line from a JNDI properties file sets the heartbeat time out to 3 seconds:
+ </p><pre class="screen">
+ connectionfactory.qpidConnectionfactory = amqp://guest:guest@clientid/test?brokerlist='tcp://localhost:5672'&heartbeat='3'
+ </pre></div></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a id="ha-security"></a>1.12.9. Security and Access Control.</h3></div></div></div><p>
+ This section outlines the HA specific aspects of security configuration.
+ Please see <a class="xref" href="chap-Messaging_User_Guide-Security.html" title="1.5. Security">Section 1.5, “Security”</a> for
+ more details on enabling authentication and setting up Access Control Lists.
+ </p><div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3><p>
+ Unless you disable authentication with <code class="literal">auth=no</code> in
+ your configuration, you <span class="emphasis"><em>must</em></span> set the options below
+ and you <span class="emphasis"><em>must</em></span> have an ACL file with at least the
+ entry described below.
+ </p><p>
+ Backups will be <span class="emphasis"><em>unable to connect to the primary</em></span> if
+ the security configuration is incorrect. See also <a class="xref" href="chapter-ha.html#ha-troubleshoot-security" title="1.12.12.2. Authentication and ACL failures">Section 1.12.12.2, “Authentication and ACL failures”</a>
+ </p></div><p>
+ When authentication is enabled you must set the credentials used by HA
+ brokers with following options:
+ </p><div class="table"><a id="ha-security-options"></a><p class="title"><strong>Table 1.29. HA Security Options</strong></p><div class="table-contents"><table border="1" summary="HA Security Options"><colgroup><col align="left" class="c1" /><col align="left" class="c2" /></colgroup><thead><tr><th align="center" colspan="2">
+ HA Security Options
+ </th></tr></thead><tbody><tr><td align="left"><p><code class="literal">ha-username</code> <em class="replaceable"><code>USER</code></em></p></td><td align="left"><p>User name for HA brokers. Note this must <span class="emphasis"><em>not</em></span> include the <code class="literal">@QPID</code> suffix.</p></td></tr><tr><td align="left"><p><code class="literal">ha-password</code> <em class="replaceable"><code>PASS</code></em></p></td><td align="left"><p>Password for HA brokers.</p></td></tr><tr><td align="left"><p><code class="literal">ha-mechanism</code> <em class="replaceable"><code>MECHANISM</code></em></p></td><td align="left">
+ <p>
+ Mechanism for HA brokers. Any mechanism you enable for
+ broker-to-broker communication can also be used by a client, so
+ do not use ha-mechanism=ANONYMOUS in a secure environment.
+ </p>
+ </td></tr></tbody></table></div></div><br class="table-break" /><p>
+ This identity is used to authorize federation links from backup to
+ primary. It is also used to authorize actions on the backup to replicate
+ primary state, for example creating queues and exchanges.
+ </p><p>
+ When authorization is enabled you must have an Access Control List with the
+ following rule to allow HA replication to function. Suppose
+ <code class="literal">ha-username</code>=<em class="replaceable"><code>USER</code></em>
+ </p><pre class="programlisting">
+acl allow <em class="replaceable"><code>USER</code></em>@QPID all all
+ </pre></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a id="ha-other-rm"></a>1.12.10. Integrating with other Cluster Resource Managers</h3></div></div></div><p>
+ To integrate with a different resource manager you must configure it to:
+ </p><div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem"><p>Start a qpidd process on each node of the cluster.</p></li><li class="listitem"><p>Restart qpidd if it crashes.</p></li><li class="listitem"><p>Promote exactly one of the brokers to primary.</p></li><li class="listitem"><p>Detect a failure and promote a new primary.</p></li></ul></div><p>
+ </p><p>
+ The <span class="command"><strong>qpid-ha</strong></span> command allows you to check if a broker is
+ primary, and to promote a backup to primary.
+ </p><p>
+ To test if a broker is the primary:
+ </p><pre class="programlisting">qpid-ha -b <em class="replaceable"><code>broker-address</code></em> status --expect=primary</pre><p>
+ This will return 0 if the broker at <em class="replaceable"><code>broker-address</code></em> is the primary,
+ non-0 otherwise.
+ </p><p>
+ To promote a broker to primary:
+ </p><pre class="programlisting">qpid-ha --cluster-manager -b <em class="replaceable"><code>broker-address</code></em> promote</pre><p>
+ </p><p>
+ Note that <code class="literal">promote</code> is considered a "cluster manager
+ only" command. Incorrect use of <code class="literal">promote</code> outside of the
+ cluster manager could create a cluster with multiple primaries. Such a
+ cluster will malfunction and lose data. "Cluster manager only" commands
+ are not accessible in <span class="command"><strong>qpid-ha</strong></span> without the
+ <code class="literal">--cluster-manager</code> option.
+ </p><p>
+ To list the full set of commands use:
+ </p><pre class="programlisting">
+qpid-ha --cluster-manager --help
+ </pre></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a id="ha-store"></a>1.12.11. Using a message store in a cluster</h3></div></div></div><p>
+ If you use a persistent store for your messages then each broker in a
+ cluster will have its own store. If the entire cluster fails and is
+ restarted, the *first* broker that becomes primary will recover from its
+ store. All the other brokers will clear their stores and get an update
+ from the primary to ensure consistency.
+ </p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a id="ha-troubleshoot"></a>1.12.12. Troubleshooting a cluster</h3></div></div></div><p>
+ This section applies to clusters that are using rgmanager as the
+ cluster manager.
+ </p><div class="section"><div class="titlepage"><div><div><h4 class="title"><a id="ha-troubleshoot-no-primary"></a>1.12.12.1. No primary broker</h4></div></div></div><p>
+ When you initially start a HA cluster, all brokers are in
+ <code class="literal">joining</code> mode. The brokers do not automatically select
+ a primary, they rely on the cluster manager <code class="literal">rgmanager</code>
+ to do so. If <code class="literal">rgmanager</code> is not running or is not
+ configured correctly, brokers will remain in the
+ <code class="literal">joining</code> state. See <a class="xref" href="chapter-ha.html#ha-rm-config" title="1.12.5. Configuring with rgmanager as resource manager">Section 1.12.5, “Configuring with <span class="command"><strong>rgmanager</strong></span> as resource manager”</a>
+ </p></div><div class="section"><div class="titlepage"><div><div><h4 class="title"><a id="ha-troubleshoot-security"></a>1.12.12.2. Authentication and ACL failures</h4></div></div></div><p>
+ If a broker is unable to establish a connection to another broker in the
+ cluster due to authentication or ACL problems the logs may contain
+ errors like the following:
+ </p><pre class="programlisting">
+info SASL: Authentication failed: SASL(-13): user not found: Password verification failed
+ </pre><p>
+ </p><pre class="programlisting">
+warning Client closed connection with 320: User anonymous@QPID federation connection denied. Systems with authentication enabled must specify ACL create link rules.
+ </pre><p>
+ </p><pre class="programlisting">
+warning Client closed connection with 320: ACL denied anonymous@QPID creating a federation link.
+ </pre><p>
+ </p><p>
+ Set the HA security configuration and ACL file as described in <a class="xref" href="chapter-ha.html#ha-security" title="1.12.9. Security and Access Control.">Section 1.12.9, “Security and Access Control.”</a>. Once the cluster is running and the primary is
+ promoted , run:
+ </p><pre class="programlisting">qpid-ha status --all</pre><p>
+ to make sure that the brokers are running as one cluster.
+ </p></div><div class="section"><div class="titlepage"><div><div><h4 class="title"><a id="ha-troubleshoot-slow-recovery"></a>1.12.12.3. Slow recovery times</h4></div></div></div><p>
+ The following configuration settings affect recovery time. The
+ values shown are examples that give fast recovery on a lightly
+ loaded system. You should run tests to determine if the values are
+ appropriate for your system and load conditions.
+ </p><div class="section"><div class="titlepage"><div><div><h5 class="title"><a id="ha-troubleshoot-cluster.conf"></a>cluster.conf:</h5></div></div></div><pre class="programlisting">
+<rm status_poll_interval=1>
+ </pre><p>
+ status_poll_interval is the interval in seconds that the
+ resource manager checks the status of managed services. This
+ affects how quickly the manager will detect failed services.
+ </p><pre class="programlisting">
+<ip address="20.0.20.200" monitor_link="yes" sleeptime="0"/>
+ </pre><p>
+ This is a virtual IP address for client traffic.
+ monitor_link="yes" means monitor the health of the network interface
+ used for the VIP. sleeptime="0" means don't delay when
+ failing over the VIP to a new address.
+ </p></div><div class="section"><div class="titlepage"><div><div><h5 class="title"><a id="ha-troubleshoot-qpidd.conf"></a>qpidd.conf</h5></div></div></div><pre class="programlisting">
+link-maintenance-interval=0.1
+ </pre><p>
+ Interval for backup brokers to check the link to the primary
+ re-connect if need be. Default 2 seconds. Can be set lower for
+ faster fail-over. Setting too low will result in excessive
+ link-checking activity on the broker.
+ </p><pre class="programlisting">
+link-heartbeat-interval=5
+ </pre><p>
+ Heartbeat interval for federation links. The HA cluster uses
+ federation links between the primary and each backup. The
+ primary can take up to twice the heartbeat interval to detect a
+ failed backup. When a sender sends a message the primary waits
+ for all backups to acknowledge before acknowledging to the
+ sender. A disconnected backup may cause the primary to block
+ senders until it is detected via heartbeat.
+ </p><p>
+ This interval is also used as the timeout for broker status
+ checks by rgmanager. It may take up to this interval for
+ rgmanager to detect a hung broker.
+ </p><p>
+ The default of 120 seconds is very high, you will probably want
+ to set this to a lower value. If set too low, under network
+ congestion or heavy load, a slow-to-respond broker may be
+ re-started by rgmanager.
+ </p></div></div><div class="section"><div class="titlepage"><div><div><h4 class="title"><a id="ha-troubleshoot-total-cluster-failure"></a>1.12.12.4. Total cluster failure</h4></div></div></div><p>
+ Note: for definition of broker states <em class="firstterm">joining</em>,
+ <em class="firstterm">catch-up</em>, <em class="firstterm">ready</em>,
+ <em class="firstterm">recovering</em> and <em class="firstterm">active</em> see
+ <a class="xref" href="chapter-ha.html#ha-broker-states" title="HA Broker States">HA Broker States</a>
+ </p><p>
+ The cluster can only guarantee availability as long as there is at
+ least one active primary broker or ready backup broker left alive.
+ If all the brokers fail simultaneously, the cluster will fail and
+ non-persistent data will be lost.
+ </p><p>
+ While there is an active primary broker, clients can get service.
+ If the active primary fails, one of the "ready" backup
+ brokers will take over, recover and become active. Note a backup
+ can only be promoted to primary if it is in the "ready"
+ state (with the exception of the first primary in a new cluster
+ where all brokers are in the "joining" state)
+ </p><p>
+ Given a stable cluster of N brokers with one active primary and
+ N-1 ready backups, the system can sustain up to N-1 failures in
+ rapid succession. The surviving broker will be promoted to active
+ and continue to give service.
+ </p><p>
+ However at this point the system <span class="emphasis"><em>cannot</em></span>
+ sustain a failure of the surviving broker until at least one of
+ the other brokers recovers, catches up and becomes a ready backup.
+ If the surviving broker fails before that the cluster will fail in
+ one of two modes (depending on the exact timing of failures)
+ </p><div class="section"><div class="titlepage"><div><div><h5 class="title"><a id="ha-troubleshoot-the-cluster-hangs"></a>1. The cluster hangs</h5></div></div></div><p>
+ All brokers are in joining or catch-up mode. rgmanager tries to
+ promote a new primary but cannot find any candidates and so
+ gives up. clustat will show that the qpidd services are running
+ but the the qpidd-primary service has stopped, something like
+ this:
+ </p><pre class="programlisting">
+Service Name Owner (Last) State
+------- ---- ----- ------ -----
+service:mrg33-qpidd-service 20.0.10.33 started
+service:mrg34-qpidd-service 20.0.10.34 started
+service:mrg35-qpidd-service 20.0.10.35 started
+service:qpidd-primary-service (20.0.10.33) stopped
+ </pre><p>
+ Eventually all brokers become stuck in "joining" mode,
+ as shown by: <code class="literal">qpid-ha status --all</code>
+ </p><p>
+ At this point you need to restart the cluster in one of the
+ following ways:
+ </p><div class="orderedlist"><ol class="orderedlist" type="1"><li class="listitem"><p>
+ Restart the entire cluster:
+ In <code class="literal">luci:<em class="replaceable"><code>your-cluster</code></em>:Nodes</code>
+ click reboot to restart the entire cluster
+ </p></li><li class="listitem"><p>
+ Stop and restart the cluster with
+ <code class="literal">ccs --stopall; ccs --startall</code>
+ </p></li><li class="listitem"><p>
+ Restart just the Qpid services:In <code class="literal">luci:<em class="replaceable"><code>your-cluster</code></em>:Service Groups</code>
+ </p><div class="orderedlist"><ol class="orderedlist" type="a"><li class="listitem"><p>Select all the qpidd (not qpidd-primary) services, click restart</p></li><li class="listitem"><p>Select the qpidd-primary service, click restart</p></li></ol></div><p>
+ </p></li><li class="listitem"><p>
+ Stop the <code class="literal">qpidd-primary</code> and
+ <code class="literal">qpidd</code> services with <code class="literal">clusvcadm</code>,
+ then restart (qpidd-primary last)
+ </p></li></ol></div><p>
+ </p></div><div class="section"><div class="titlepage"><div><div><h5 class="title"><a id="ha-troubleshoot-the-cluster-reboots"></a>2. The cluster reboots</h5></div></div></div><p>
+ A new primary is promoted and the cluster is functional but all
+ non-persistent data from before the failure is lost.
+ </p></div></div><div class="section"><div class="titlepage"><div><div><h4 class="title"><a id="ha-troubleshoot-fencing-and-network-partitions"></a>1.12.12.5. Fencing and network partitions</h4></div></div></div><p>
+ A network partition is a a network failure that divides the
+ cluster into two or more sub-clusters, where each broker can
+ communicate with brokers in its own sub-cluster but not with
+ brokers in other sub-clusters. This condition is also referred to
+ as a "split brain".
+ </p><p>
+ Nodes in one sub-cluster can't tell whether nodes in other
+ sub-clusters are dead or are still running but disconnected. We
+ cannot allow each sub-cluster to independently declare its own
+ qpidd primary and start serving clients, as the cluster will
+ become inconsistent. We must ensure only one sub-cluster continues
+ to provide service.
+ </p><p>
+ A <span class="emphasis"><em>quorum</em></span> determines which sub-cluster
+ continues to operate, and <span class="emphasis"><em>power fencing</em></span>
+ ensures that nodes in non-quorate sub-clusters cannot attempt to
+ provide service inconsistently. For more information see:
+ </p><p>
+ https://access.redhat.com/site/documentation/en-US/Red_Hat_Enterprise_Linux/6/html-single/High_Availability_Add-On_Overview/index.html,
+ chapter 2. Quorum and 4. Fencing.
+ </p></div></div><div class="footnotes"><br /><hr align="left" width="100" /><div class="footnote" id="ftn.idm221086980816"><p><a class="para" href="#idm221086980816"><sup class="para">[1] </sup></a>
+ You can control the maximum number of messages in the buffer by setting the
+ client's <code class="literal">capacity</code>. For details of how to set the capacity
+ in client code see "Using the Qpid Messaging API" in
+ <em class="citetitle">Programming in Apache Qpid</em>.
+ </p></div><div class="footnote" id="ftn.idm221087556864"><p><a class="para" href="#idm221087556864"><sup class="para">[2] </sup></a>
+ Clients must use "at-least-once" reliability to enable re-send of unacknowledged
+ messages. This is the default behaviour, no options need be set to enable it. For
+ details of client addressing options see "Using the Qpid Messaging API"
+ in <em class="citetitle">Programming in Apache Qpid</em>.
+ </p></div><div class="footnote" id="ftn.idm221084088000"><p><a class="para" href="#idm221084088000"><sup class="para">[3] </sup></a>
+ The full grammar for the URL is:
+ </p><pre class="programlisting">
+url = ["amqp:"][ user ["/" password] "@" ] addr ("," addr)*
+addr = tcp_addr / rmda_addr / ssl_addr / ...
+tcp_addr = ["tcp:"] host [":" port]
+rdma_addr = "rdma:" host [":" port]
+ssl_addr = "ssl:" host [":" port]'
+ </pre></div></div></div><div class="navfooter"><hr /><table summary="Navigation footer" width="100%"><tr><td align="left" width="40%"><a accesskey="p" href="Using-message-groups.html">Prev</a> </td><td align="center" width="20%"><a accesskey="u" href="ch01.html">Up</a></td><td align="right" width="40%"> <a accesskey="n" href="ha-queue-replication.html">Next</a></td></tr><tr><td align="left" valign="top" width="40%">1.11. 
+ Using Message Groups
+  </td><td align="center" width="20%"><a accesskey="h" href="index.html">Home</a></td><td align="right" valign="top" width="40%"> 1.13. Replicating Queues with the HA module</td></tr></table></div></div>
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