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+
+ <div id="-middle-content">
+ <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.idm140045948288240" id="idm140045948288240"><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.idm140045950151440" id="idm140045950151440"><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" class="table" 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.idm140045949630688" id="idm140045949630688"><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" class="table" 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.idm140045948288240"><p><a class="para" href="#idm140045948288240"><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.idm140045950151440"><p><a class="para" href="#idm140045950151440"><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.idm140045949630688"><p><a class="para" href="#idm140045949630688"><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
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+
+ <div id="-middle-content">
+ <div class="docbook"><div class="navheader"><table summary="Navigation header" width="100%"><tr><th align="center" colspan="3">1.13. Replicating Queues with the HA module</th></tr><tr><td align="left" width="20%"><a accesskey="p" href="chapter-ha.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="chapter-Managing-CPP-Broker.html">Next</a></td></tr></table><hr /></div><div class="section"><div class="titlepage"><div><div><h2 class="title"><a id="ha-queue-replication"></a>1.13. Replicating Queues with the HA module</h2></div></div></div><p>
+ As well as support for an active-passive cluster, the
+ HA module allows you to replicate individual queues,
+ even if the brokers are not in a cluster. The <em class="firstterm">original</em>
+ queue is used as normal. The <em class="firstterm">replica</em> queue is
+ updated automatically as messages are added to or removed from the original
+ queue.
+ </p><div class="warning" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Warning</h3><p>
+ It is not safe to modify the replica queue
+ other than via the automatic updates from the original. Adding or removing
+ messages on the replica queue will make replication inconsistent and may
+ cause message loss.
+ The HA module does <span class="emphasis"><em>not</em></span> enforce
+ restricted access to the replica queue (as it does in the case of a cluster)
+ so it is up to the application to ensure the replica is not used until it has
+ been disconnected from the original.
+ </p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a id="idm140045951652432"></a>1.13.1. Replicating queues</h3></div></div></div><p>
+ To create a replica queue, the HA module must be
+ loaded on both the original and replica brokers (it is loaded by default.)
+ You also need to set the configuration option:
+ </p><pre class="programlisting">
+ ha-queue-replication=yes
+ </pre><p>
+ to enable this feature on a stand-alone broker. It is automatically
+ enabled for brokers that are part of a cluster.
+ </p><p>
+ Suppose that <span class="command"><strong>myqueue</strong></span> is a queue on
+ <span class="command"><strong>node1</strong></span> and we want to create a replica of
+ <span class="command"><strong>myqueue</strong></span> on <span class="command"><strong>node2</strong></span> (where both brokers
+ are using the default AMQP port.) This is accomplished by the command:
+ </p><pre class="programlisting">
+ qpid-config --broker=node2 add queue --start-replica node1 myqueue
+ </pre><p>
+ If <span class="command"><strong>myqueue</strong></span> already exists on the replica
+ broker you can start replication from the original queue like this:
+ </p><pre class="programlisting">
+ qpid-ha replicate -b node2 node1 myqueue
+ </pre><p>
+ </p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a id="idm140045952711648"></a>1.13.2. Replicating queues between clusters</h3></div></div></div><p>
+ You can replicate queues between two standalone brokers, between a
+ standalone broker and a cluster, or between two clusters (see <a class="xref" href="chapter-ha.html" title="1.12. Active-Passive Messaging Clusters">Section 1.12, “Active-Passive Messaging Clusters”</a>.) For failover in a cluster there are two cases to
+ consider.
+ </p><div class="orderedlist"><ol class="orderedlist" type="1"><li class="listitem"><p>
+ When the <span class="emphasis"><em>original</em></span> queue is on the active node
+ of a cluster, failover is automatic. If the active node
+ fails, the replication link will automatically reconnect and the
+ replica will continue to be updated from the new primary.
+ </p></li><li class="listitem"><p>
+ When the <span class="emphasis"><em>replica</em></span> queue is on the active node of a
+ cluster, there is no automatic failover. However you can use the
+ following workaround.
+ </p></li></ol></div><div class="section"><div class="titlepage"><div><div><h4 class="title"><a id="idm140045948386928"></a>1.13.2.1. Work around for fail-over of replica queue in a cluster</h4></div></div></div><p>
+ When a primary broker fails the cluster resource manager calls a script
+ to promote a backup broker to be the new primary. By default this script
+ is <code class="filename">/etc/init.d/qpidd-primary</code> but you can modify
+ that in your <code class="filename">cluster.conf</code> file (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><p>
+ You can modify this script (on each host in your cluster) by adding
+ commands to create your replica queues just before the broker is
+ promoted, as indicated in the following exceprt from the script:
+ </p><pre class="programlisting">
+start() {
+ service qpidd start
+ echo -n $"Promoting qpid daemon to cluster primary: "
+ ################################
+ #### Add your commands here ####
+ ################################
+ $QPID_HA -b localhost:$QPID_PORT promote
+ [ "$?" -eq 0 ] && success || failure
+}
+ </pre><p>
+ Your commands will be run, and your replicas created, whenever
+ the system fails over to a new primary.
+ </p></div></div></div><div class="navfooter"><hr /><table summary="Navigation footer" width="100%"><tr><td align="left" width="40%"><a accesskey="p" href="chapter-ha.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="chapter-Managing-CPP-Broker.html">Next</a></td></tr><tr><td align="left" valign="top" width="40%">1.12. Active-Passive Messaging Clusters </td><td align="center" width="20%"><a accesskey="h" href="index.html">Home</a></td><td align="right" valign="top" width="40%"> Chapter 2. 
+ Managing the AMQP Messaging Broker
+ </td></tr></table></div></div>
+
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