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Posted to docs@httpd.apache.org by Sander Temme <sc...@apache.org> on 2012/01/07 20:22:04 UTC
Fwd: svn commit: r1228700 - in /httpd/httpd/trunk/docs: STATUS manual/mod/mod_heartbeat.xml manual/mod/mod_heartmonitor.xml manual/mod/mod_watchdog.xml manual/mod/mod_watchdog.xml.meta
Folks,
I've put in some updates to the mod_heart* modules, taken from the README supplied with the modules and some perusal of the source code. I have not run these as I'm too lazy to set up the servers. Review would be appreciated, especially by the original authors (Cc), before backport to 2.4.x.
Also added a doc file for mod_watchdog. Question for the docs folks: since this one is only of interest for consumption by other modules, how much documentation should we supply in the user-facing pages? I said "this module defines programmatic hooks"... do we need to define what the hook handler prototypes are? That's more like developer documentation. Thoughts?
S.
Begin forwarded message:
> From: sctemme@apache.org
> Subject: svn commit: r1228700 - in /httpd/httpd/trunk/docs: STATUS manual/mod/mod_heartbeat.xml manual/mod/mod_heartmonitor.xml manual/mod/mod_watchdog.xml manual/mod/mod_watchdog.xml.meta
> Date: January 7, 2012 11:10:29 AM PST
> To: cvs@httpd.apache.org
> Reply-To: dev@httpd.apache.org
>
> Author: sctemme
> Date: Sat Jan 7 19:10:28 2012
> New Revision: 1228700
>
> URL: http://svn.apache.org/viewvc?rev=1228700&view=rev
> Log:
> Update heartbeat module documentation, add documentation for mod_watchdog
>
> Added:
> httpd/httpd/trunk/docs/manual/mod/mod_watchdog.xml (with props)
> httpd/httpd/trunk/docs/manual/mod/mod_watchdog.xml.meta
> Modified:
> httpd/httpd/trunk/docs/STATUS
> httpd/httpd/trunk/docs/manual/mod/mod_heartbeat.xml
> httpd/httpd/trunk/docs/manual/mod/mod_heartmonitor.xml
>
> Modified: httpd/httpd/trunk/docs/STATUS
> URL: http://svn.apache.org/viewvc/httpd/httpd/trunk/docs/STATUS?rev=1228700&r1=1228699&r2=1228700&view=diff
> ==============================================================================
> --- httpd/httpd/trunk/docs/STATUS (original)
> +++ httpd/httpd/trunk/docs/STATUS Sat Jan 7 19:10:28 2012
> @@ -56,12 +56,8 @@ To Do List
> Start is in expr.xml, igalic is working on this
>
> - modules docs
> - - the follwing modules added since 2.2 lack documentation
> + - the following modules added since 2.2 lack documentation
> - mod_serf
> - - mod_watchdog
> - - mod_heartbeat
> - - mod_heartmonitor
> - - mod_lbmethod_heartbeat
> - mpm_simple
> the list may be incomplete
> maybe some of the modules will not be included in 2.4
>
> Modified: httpd/httpd/trunk/docs/manual/mod/mod_heartbeat.xml
> URL: http://svn.apache.org/viewvc/httpd/httpd/trunk/docs/manual/mod/mod_heartbeat.xml?rev=1228700&r1=1228699&r2=1228700&view=diff
> ==============================================================================
> --- httpd/httpd/trunk/docs/manual/mod/mod_heartbeat.xml (original)
> +++ httpd/httpd/trunk/docs/manual/mod/mod_heartbeat.xml Sat Jan 7 19:10:28 2012
> @@ -35,21 +35,66 @@ that advertises the servers current conn
> will be running on a proxy server with <module>mod_lbmethod_heartbeat</module> loaded, which allows
> <directive module="mod_proxy">ProxyPass</directive> to use the "heartbeat" <em>lbmethod</em> inside
> of <directive module="mod_proxy">ProxyPass</directive>.</p>
> +<p>
> + <module>mod_heartbeat</module> itself is loaded on the origin server(s) that serve requests
> + through the proxy server(s).
> +</p>
> +
> + <note type="warning">
> + To use <module>mod_heartbeat</module>,
> + <module>mod_status</module> and <module>mod_watchdog</module>
> + must be either a static modules or, if a dynamic module, it must
> + be loaded before <module>mod_heartbeat</module>.
> + </note>
> +
> </summary>
>
> +<section id="consuming">
> + <title>Consuming mod_heartbeat Output</title>
> + <p>
> + Every 1 second, this module generates a single multicast UDP
> + packet, containing the number of busy and idle workers. The
> + packet is a simple ASCII format, similiar to GET query parameters
> + in HTTP.
> + </p>
> +
> +<example><title>An Example Packet</title>
> +v=1&ready=75&busy=0
> +</example>
> +
> + <p>
> + Consumers should handle new variables besides busy and ready,
> + separated by '&', being added in the future.
> + </p>
> +
> +</section>
> +
> +<section id="miscellaneous">
> +<title>Miscellaneous</title>
> +<p>The interval of 1 seconds is controlled by the HEARTBEAT_INTERVAL
> +compile time define. This is not currently tunable at run time. To make
> +this module send the status packet more often, you must add to the
> +CFLAGS used to compile the module to include:</p>
> +<example>-DHEARTBEAT_INTERVAL=3</example>
> +<p>Would cause the broadcasts to be sent every 3 seconds.</p>
> +</section>
> +
> <directivesynopsis>
> <name>HeartbeatAddress</name>
> -<description>Address to send heartbeat requests</description>
> +<description>Multicast address for heartbeat packets</description>
> <syntax>HeartbeatAddress <var>addr:port</var></syntax>
> <default>disabled</default>
> <contextlist><context>server config</context></contextlist>
>
> <usage>
> - <p>The <directive>HeartbeatAddress</directive> directive specifies the
> - address <module>mod_heartbeat</module> will send status information to. This
> - address will usually corrspond to a configured <directive
> - module="mod_heartmonitor">HeartbeatListen</directive> on a frontend
> - proxy system. </p>
> +<p>The <directive>HeartbeatAddress</directive> directive specifies the
> +multicast address to which <module>mod_heartbeat</module> will send
> +status information. This address will usually correspond to a configured
> + <directive module="mod_heartmonitor">HeartbeatListen</directive> on a
> +frontend proxy system.</p>
> +<example>
> +HeartbeatAddress 239.0.0.1:27999
> +</example>
> </usage>
> </directivesynopsis>
>
>
> Modified: httpd/httpd/trunk/docs/manual/mod/mod_heartmonitor.xml
> URL: http://svn.apache.org/viewvc/httpd/httpd/trunk/docs/manual/mod/mod_heartmonitor.xml?rev=1228700&r1=1228699&r2=1228700&view=diff
> ==============================================================================
> --- httpd/httpd/trunk/docs/manual/mod/mod_heartmonitor.xml (original)
> +++ httpd/httpd/trunk/docs/manual/mod/mod_heartmonitor.xml Sat Jan 7 19:10:28 2012
> @@ -20,19 +20,19 @@
> limitations under the License.
> -->
>
> -<modulesynopsis metafile="mod_heartbeat.xml.meta">
> +<modulesynopsis metafile="mod_heartmonitor.xml.meta">
>
> <name>mod_heartmonitor</name>
> <description>centralized monitor for mod_heartbeat origin servers</description>
> <status>Experimental</status>
> -<sourcefile>mod_heartmonitor</sourcefile>
> +<sourcefile>mod_heartmonitor.c</sourcefile>
> <identifier>heartmonitor_module</identifier>
> <compatibility>Available in Apache 2.3 and later</compatibility>
>
> <summary>
> <p>
> <module>mod_heartmonitor</module> listens for server status messages generated
> -by <module>mod_heartbeat</module> enabled servers and makes their status
> +by <module>mod_heartbeat</module> enabled origin servers and makes their status
> available to <module>mod_lbmethod_heartbeat</module>. This allows
> <directive module="mod_proxy">ProxyPass</directive> to use the "heartbeat"
> <em>lbmethod</em> inside of <directive module="mod_proxy">ProxyPass</directive>.
> @@ -41,22 +41,34 @@ available to <module>mod_lbmethod_heartb
> <p>This module uses the services of <module>mod_slotmem_shm</module> when
> available instead of flat-file storage. No configuration is required to
> use <module>mod_slotmem_shm</module>.</p>
> +
> + <note type="warning">
> + To use <module>mod_heartmonitor</module>,
> + <module>mod_status</module> and <module>mod_watchdog</module>
> + must be either a static modules or, if a dynamic module, it must
> + be loaded before <module>mod_heartmonitor</module>.
> + </note>
> +
> </summary>
>
> <directivesynopsis>
> <name>HeartbeatListen</name>
> -<description>address to listen for incoming heartbeat requests </description>
> +<description>multicast address to listen for incoming heartbeat requests </description>
> <syntax>HeartbeatListen<var>addr:port</var></syntax>
> <default>disabled</default>
> <contextlist><context>server config</context></contextlist>
>
> <usage>
> <p>The <directive>HeartbeatListen</directive> directive specifies the
> - address the server will listen on for status information from
> + multicast address on which the server will listen for status information from
> <module>mod_heartbeat</module>-enabled servers. This
> address will usually corrspond to a configured <directive
> module="mod_heartbeat">HeartbeatAddress</directive> on an origin server.
> </p>
> +
> + <example>
> + HeartbeatListen 239.0.0.1:27999
> + </example>
>
> <p> This module is inactive until this directive is used.</p>
> </usage>
> @@ -88,7 +100,7 @@ heartbeat requests to this server</descr
> <p>The <directive>HeartbeatMaxServers</directive> directive specifies the
> maximum number of servers that will be sending requests to this monitor
> server. It is used to control the size of the shared memory allocated
> - to store the heartbeat info.</p>
> + to store the heartbeat info when <module>mod_slotmem_shm</module> is in use.</p>
> </usage>
> </directivesynopsis>
> </modulesynopsis>
>
> Added: httpd/httpd/trunk/docs/manual/mod/mod_watchdog.xml
> URL: http://svn.apache.org/viewvc/httpd/httpd/trunk/docs/manual/mod/mod_watchdog.xml?rev=1228700&view=auto
> ==============================================================================
> --- httpd/httpd/trunk/docs/manual/mod/mod_watchdog.xml (added)
> +++ httpd/httpd/trunk/docs/manual/mod/mod_watchdog.xml Sat Jan 7 19:10:28 2012
> @@ -0,0 +1,60 @@
> +<?xml version="1.0"?>
> +<!DOCTYPE modulesynopsis SYSTEM "../style/modulesynopsis.dtd">
> +<?xml-stylesheet type="text/xsl" href="../style/manual.en.xsl"?>
> +
> +<!--
> + Licensed to the Apache Software Foundation (ASF) under one or more
> + contributor license agreements. See the NOTICE file distributed with
> + this work for additional information regarding copyright ownership.
> + The ASF licenses this file to You under the Apache License, Version 2.0
> + (the "License"); you may not use this file except in compliance with
> + the License. You may obtain a copy of the License at
> +
> + http://www.apache.org/licenses/LICENSE-2.0
> +
> + Unless required by applicable law or agreed to in writing, software
> + distributed under the License is distributed on an "AS IS" BASIS,
> + WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
> + See the License for the specific language governing permissions and
> + limitations under the License.
> +-->
> +
> +<modulesynopsis metafile="mod_watchdog.xml.meta">
> +<name>mod_watchdog</name>
> +<description>provides infrastructure for other modules to periodically run
> + tasks</description>
> +<status>Base</status>
> +<sourcefile>mod_watchdog.c</sourcefile>
> +<identifier>watchdog_module</identifier>
> +<compatibility>Available in Apache 2.3 and later</compatibility>
> +
> +<summary>
> +<p><module>mod_watchdog</module> defines programmatic hooks for other modules to
> +periodically run tasks. These modules can register handlers for
> +<module>mod_watchdog</module> hooks. Currently, the following modules in the
> +Apache distribution use this functionality:</p>
> +<ul>
> +<li><module>mod_heartbeat</module></li>
> +<li><module>mod_heartmonitor</module></li>
> +</ul>
> +<note type="warning">
> +To allow a module to use <module>mod_watchdog</module> functionality,
> +<module>mod_watchdog</module> itself must be statically linked to the server
> +core or, if a dynamic module, be loaded before the calling module.
> +</note>
> +</summary>
> +
> +<directivesynopsis>
> +<name>WatchdogInterval</name>
> +<description>Watchdog interval in seconds</description>
> +<syntax>WatchdogInterval <var>number-of-seconds</var></syntax>
> +<default>WatchdogInterval 1</default>
> +<contextlist><context>server config</context></contextlist>
> +
> +<usage>
> +Sets the interval at which the watchdog_step hook runs. Default is to run every
> +second.
> +</usage>
> +</directivesynopsis>
> +</modulesynopsis>
> +
>
> Propchange: httpd/httpd/trunk/docs/manual/mod/mod_watchdog.xml
> ------------------------------------------------------------------------------
> svn:eol-style = native
>
> Added: httpd/httpd/trunk/docs/manual/mod/mod_watchdog.xml.meta
> URL: http://svn.apache.org/viewvc/httpd/httpd/trunk/docs/manual/mod/mod_watchdog.xml.meta?rev=1228700&view=auto
> ==============================================================================
> --- httpd/httpd/trunk/docs/manual/mod/mod_watchdog.xml.meta (added)
> +++ httpd/httpd/trunk/docs/manual/mod/mod_watchdog.xml.meta Sat Jan 7 19:10:28 2012
> @@ -0,0 +1,12 @@
> +<?xml version="1.0" encoding="UTF-8" ?>
> +<!-- GENERATED FROM XML: DO NOT EDIT -->
> +
> +<metafile reference="mod_watchdog.xml">
> + <basename>mod_watchdog</basename>
> + <path>/mod/</path>
> + <relpath>..</relpath>
> +
> + <variants>
> + <variant>en</variant>
> + </variants>
> +</metafile>
>
>
--
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PGP FP: FC5A 6FC6 2E25 2DFD 8007 EE23 9BB8 63B0 F51B B88A
View my availability: http://tungle.me/sctemme
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Re: svn commit: r1228700 - in /httpd/httpd/trunk/docs: STATUS manual/mod/mod_heartbeat.xml manual/mod/mod_heartmonitor.xml manual/mod/mod_watchdog.xml manual/mod/mod_watchdog.xml.meta
Posted by Sander Temme <sc...@apache.org>.
On Jan 7, 2012, at 1:08 PM, Rainer Jung wrote:
>> hook handler prototypes are? That's more like developer documentation. Thoughts?
>
> I don't know about the history of similar decisions, but IMHO what you wrote is good enough for 2.4.0.
Sounds good.
>>> +<p>The interval of 1 seconds is controlled by the HEARTBEAT_INTERVAL
>>> +compile time define. This is not currently tunable at run time. To make
>>> +this module send the status packet more often, you must add to the
>>> +CFLAGS used to compile the module to include:</p>
>>> +<example>-DHEARTBEAT_INTERVAL=3</example>
>>> +<p>Would cause the broadcasts to be sent every 3 seconds.</p>
>>> +</section>
>
> "more often" than 1 second does not match the example "3 seconds" ;)
> I guess more often is not possible (if resolution is seconds), so it would be "less often"?
>
> More important: I think this is totally wrong. The define exists, but I couldn't find any place in the code, which is influenced by it. I *guess* it uses the global watchdog interval configured for mod_watchdog.
Yep, it's not used. And WatchdogInterval in mod_watchdog should do the trick. Perhaps an early approach soon abandoned? Removed from docs.
>>> +<p>The<directive>HeartbeatAddress</directive> directive specifies the
>>> +multicast address to which<module>mod_heartbeat</module> will send
>>> +status information. This address will usually correspond to a configured
>>> +<directive module="mod_heartmonitor">HeartbeatListen</directive> on a
>>> +frontend proxy system.</p>
>>> +<example>
>>> +HeartbeatAddress 239.0.0.1:27999
>>> +</example>
>>> </usage>
>>> </directivesynopsis>
>
> Should we note, that Multicast needs to be enabled on both notes and routing needs to be set up, so that the multicast packets from the origin server can reach the proxy? On the one hand it is obvious, on the other hand not unlikely to be the typical first problem people run into.
I'm +1 on a note, but don't think we should tell the story on setting up IP Multicast. I omitted this mainly because I don't know the story well enough. Same for IPv6 address examples.
>>> +<note type="warning">
>>> + To use<module>mod_heartmonitor</module>,
>>> +<module>mod_status</module> and<module>mod_watchdog</module>
>>> + must be either a static modules or, if a dynamic module, it must
>>> + be loaded before<module>mod_heartmonitor</module>.
>>> +</note>
>>> +
>
> ??
The README talks only about mod_status. I added mod_watchdog because mod_heart* has a hard dependency on its symbols. The mod_status dependency is not hard (mod_heartbeat loads without mod_status loaded, or with mod_status later in the config), but not having actually run this I don't know what more subtle issues might arise.
Removed the orphaned singular "it" must be loaded.
>>> +<example>
>>> + HeartbeatListen 239.0.0.1:27999
>>> +</example>
>
> Same remark concerning the use of multicast as above.
>
>>> <p> This module is inactive until this directive is used.</p>
>>> </usage>
>>> @@ -88,7 +100,7 @@ heartbeat requests to this server</descr
>>> <p>The<directive>HeartbeatMaxServers</directive> directive specifies the
>>> maximum number of servers that will be sending requests to this monitor
>>> server. It is used to control the size of the shared memory allocated
>>> - to store the heartbeat info.</p>
>>> + to store the heartbeat info when<module>mod_slotmem_shm</module> is in use.</p>
>
> Can this be changed using graceful restart? Only for flat file or also for shm?
This gets set up in the post_config hook handler. I forget whether that gets called on a graceful, and have not analyzed whether the graceful restart case gets handled properly. I suspect this depends on the behaviour of the slotmem provider.
In the file case, it seems that very few assumptions about the state of the world are made.
> Typo: "corrspond" -> "correspond"
Thank you.
> Additional info: it seems the data used for the load balancer is updated about every 5 seconds (define HM_UPDATE_SEC). More precisely it seems the heartmonitor is called by watchdog (with interval 0 seconds, but watchdog sleep at least 100ms), then updates the data from what is had previously read, then loops for 5 seconds reading new data and then returns to watchdog. This is done one one thread per child, but a mutex guarantees, that it only runs in one child at every time. Hope I'm right.
I hope so, too.
> Furthermore the heartmonitor contains some additional code to handle POST requests directed to it and reading usage data directly from the POST body (in addition to the multicast method).
>
> I think the current info in mod_lbmethod_heartbeat.xml is confusing. It contains:
I did not edit that doc.
> "This modules load balancing algorithm favors servers with more ready (idle) capacity over time, but does not select the server with the most ready capacity every time. Servers that have 0 active clients are penalized, with the assumption that they are not fully initialized."
>
> As far as I can see in the code, it randomly chooses one of the idle origin server slots based on the last received heartbeat data. Another equivalent formulation would be: it does a weighted balancing to the origin servers, where the weights are proportional to the idle (ready) slots reported with the last heartbeat message.
>
> I couldn't find code that penalizes servers with 0 active clients.
See Eric's response.
> It seems the heartbeat lb opens the data file for each request. So if I'm right, using slotmem is highly recommended for performance reasons.
That seems to be a safe bet.
>>> +<usage>
>>> +Sets the interval at which the watchdog_step hook runs. Default is to run every
>>> +second.
>>> +</usage>
>>> +</directivesynopsis>
>>> +</modulesynopsis>
>>> +
>
> We could mention, that there are two ways (and APIs) a module can use mod_watchdog. Either synchronously called every watchdog interval seconds, or running on a separate thread called every interval seconds, where interval is given during the setup.
>
> Furthermore modules can tell mod_watchdog, whether the tasks should be run in each child independently, or coordinated by a mutex.
Again, that would be Developer Documentation. Should "we" put something under docs/manual/developer to discuss how the module is used?
S.
--
sctemme@apache.org http://www.temme.net/sander/
PGP FP: FC5A 6FC6 2E25 2DFD 8007 EE23 9BB8 63B0 F51B B88A
View my availability: http://tungle.me/sctemme
Re: svn commit: r1228700 - in /httpd/httpd/trunk/docs: STATUS manual/mod/mod_heartbeat.xml manual/mod/mod_heartmonitor.xml manual/mod/mod_watchdog.xml manual/mod/mod_watchdog.xml.meta
Posted by Sander Temme <sc...@apache.org>.
On Jan 7, 2012, at 1:08 PM, Rainer Jung wrote:
>> hook handler prototypes are? That's more like developer documentation. Thoughts?
>
> I don't know about the history of similar decisions, but IMHO what you wrote is good enough for 2.4.0.
Sounds good.
>>> +<p>The interval of 1 seconds is controlled by the HEARTBEAT_INTERVAL
>>> +compile time define. This is not currently tunable at run time. To make
>>> +this module send the status packet more often, you must add to the
>>> +CFLAGS used to compile the module to include:</p>
>>> +<example>-DHEARTBEAT_INTERVAL=3</example>
>>> +<p>Would cause the broadcasts to be sent every 3 seconds.</p>
>>> +</section>
>
> "more often" than 1 second does not match the example "3 seconds" ;)
> I guess more often is not possible (if resolution is seconds), so it would be "less often"?
>
> More important: I think this is totally wrong. The define exists, but I couldn't find any place in the code, which is influenced by it. I *guess* it uses the global watchdog interval configured for mod_watchdog.
Yep, it's not used. And WatchdogInterval in mod_watchdog should do the trick. Perhaps an early approach soon abandoned? Removed from docs.
>>> +<p>The<directive>HeartbeatAddress</directive> directive specifies the
>>> +multicast address to which<module>mod_heartbeat</module> will send
>>> +status information. This address will usually correspond to a configured
>>> +<directive module="mod_heartmonitor">HeartbeatListen</directive> on a
>>> +frontend proxy system.</p>
>>> +<example>
>>> +HeartbeatAddress 239.0.0.1:27999
>>> +</example>
>>> </usage>
>>> </directivesynopsis>
>
> Should we note, that Multicast needs to be enabled on both notes and routing needs to be set up, so that the multicast packets from the origin server can reach the proxy? On the one hand it is obvious, on the other hand not unlikely to be the typical first problem people run into.
I'm +1 on a note, but don't think we should tell the story on setting up IP Multicast. I omitted this mainly because I don't know the story well enough. Same for IPv6 address examples.
>>> +<note type="warning">
>>> + To use<module>mod_heartmonitor</module>,
>>> +<module>mod_status</module> and<module>mod_watchdog</module>
>>> + must be either a static modules or, if a dynamic module, it must
>>> + be loaded before<module>mod_heartmonitor</module>.
>>> +</note>
>>> +
>
> ??
The README talks only about mod_status. I added mod_watchdog because mod_heart* has a hard dependency on its symbols. The mod_status dependency is not hard (mod_heartbeat loads without mod_status loaded, or with mod_status later in the config), but not having actually run this I don't know what more subtle issues might arise.
Removed the orphaned singular "it" must be loaded.
>>> +<example>
>>> + HeartbeatListen 239.0.0.1:27999
>>> +</example>
>
> Same remark concerning the use of multicast as above.
>
>>> <p> This module is inactive until this directive is used.</p>
>>> </usage>
>>> @@ -88,7 +100,7 @@ heartbeat requests to this server</descr
>>> <p>The<directive>HeartbeatMaxServers</directive> directive specifies the
>>> maximum number of servers that will be sending requests to this monitor
>>> server. It is used to control the size of the shared memory allocated
>>> - to store the heartbeat info.</p>
>>> + to store the heartbeat info when<module>mod_slotmem_shm</module> is in use.</p>
>
> Can this be changed using graceful restart? Only for flat file or also for shm?
This gets set up in the post_config hook handler. I forget whether that gets called on a graceful, and have not analyzed whether the graceful restart case gets handled properly. I suspect this depends on the behaviour of the slotmem provider.
In the file case, it seems that very few assumptions about the state of the world are made.
> Typo: "corrspond" -> "correspond"
Thank you.
> Additional info: it seems the data used for the load balancer is updated about every 5 seconds (define HM_UPDATE_SEC). More precisely it seems the heartmonitor is called by watchdog (with interval 0 seconds, but watchdog sleep at least 100ms), then updates the data from what is had previously read, then loops for 5 seconds reading new data and then returns to watchdog. This is done one one thread per child, but a mutex guarantees, that it only runs in one child at every time. Hope I'm right.
I hope so, too.
> Furthermore the heartmonitor contains some additional code to handle POST requests directed to it and reading usage data directly from the POST body (in addition to the multicast method).
>
> I think the current info in mod_lbmethod_heartbeat.xml is confusing. It contains:
I did not edit that doc.
> "This modules load balancing algorithm favors servers with more ready (idle) capacity over time, but does not select the server with the most ready capacity every time. Servers that have 0 active clients are penalized, with the assumption that they are not fully initialized."
>
> As far as I can see in the code, it randomly chooses one of the idle origin server slots based on the last received heartbeat data. Another equivalent formulation would be: it does a weighted balancing to the origin servers, where the weights are proportional to the idle (ready) slots reported with the last heartbeat message.
>
> I couldn't find code that penalizes servers with 0 active clients.
See Eric's response.
> It seems the heartbeat lb opens the data file for each request. So if I'm right, using slotmem is highly recommended for performance reasons.
That seems to be a safe bet.
>>> +<usage>
>>> +Sets the interval at which the watchdog_step hook runs. Default is to run every
>>> +second.
>>> +</usage>
>>> +</directivesynopsis>
>>> +</modulesynopsis>
>>> +
>
> We could mention, that there are two ways (and APIs) a module can use mod_watchdog. Either synchronously called every watchdog interval seconds, or running on a separate thread called every interval seconds, where interval is given during the setup.
>
> Furthermore modules can tell mod_watchdog, whether the tasks should be run in each child independently, or coordinated by a mutex.
Again, that would be Developer Documentation. Should "we" put something under docs/manual/developer to discuss how the module is used?
S.
--
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Re: Fwd: svn commit: r1228700 - in /httpd/httpd/trunk/docs: STATUS
manual/mod/mod_heartbeat.xml manual/mod/mod_heartmonitor.xml
manual/mod/mod_watchdog.xml manual/mod/mod_watchdog.xml.meta
Posted by Eric Covener <co...@gmail.com>.
od_lbmethod_heartbeat.c has this while reading the data:
199 if (server->busy == 0 && server->ready != 0) {
200 /* Server has zero threads active, but lots of them ready,
201 * it likely just started up, so lets /4 the number ready,
202 * to prevent us from completely flooding it with all new
203 * requests.
204 */
205 server->ready = server->ready / 4;
206 }
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Re: Fwd: svn commit: r1228700 - in /httpd/httpd/trunk/docs: STATUS
manual/mod/mod_heartbeat.xml manual/mod/mod_heartmonitor.xml manual/mod/mod_watchdog.xml
manual/mod/mod_watchdog.xml.meta
Posted by Rainer Jung <ra...@kippdata.de>.
On 07.01.2012 20:22, Sander Temme wrote:
> Folks,
>
> I've put in some updates to the mod_heart* modules, taken from the README supplied with the modules and some perusal of the source code. I have not run these as I'm too lazy to set up the servers. Review would be appreciated, especially by the original authors (Cc), before backport to 2.4.x.
I added some comments inline, just based on reading your docs.
> Also added a doc file for mod_watchdog. Question for the docs folks: since this one is only of interest for consumption by other modules, how much documentation should we supply in the user-facing pages? I said "this module defines programmatic hooks"... do we need to define what the hook handler prototypes are? That's more like developer documentation. Thoughts?
I don't know about the history of similar decisions, but IMHO what you
wrote is good enough for 2.4.0.
>> Modified: httpd/httpd/trunk/docs/manual/mod/mod_heartbeat.xml
>> URL: http://svn.apache.org/viewvc/httpd/httpd/trunk/docs/manual/mod/mod_heartbeat.xml?rev=1228700&r1=1228699&r2=1228700&view=diff
>> ==============================================================================
>> --- httpd/httpd/trunk/docs/manual/mod/mod_heartbeat.xml (original)
>> +++ httpd/httpd/trunk/docs/manual/mod/mod_heartbeat.xml Sat Jan 7 19:10:28 2012
>> @@ -35,21 +35,66 @@ that advertises the servers current conn
>> will be running on a proxy server with<module>mod_lbmethod_heartbeat</module> loaded, which allows
>> <directive module="mod_proxy">ProxyPass</directive> to use the "heartbeat"<em>lbmethod</em> inside
>> of<directive module="mod_proxy">ProxyPass</directive>.</p>
>> +<p>
>> +<module>mod_heartbeat</module> itself is loaded on the origin server(s) that serve requests
>> + through the proxy server(s).
>> +</p>
>> +
>> +<note type="warning">
>> + To use<module>mod_heartbeat</module>,
>> +<module>mod_status</module> and<module>mod_watchdog</module>
>> + must be either a static modules or, if a dynamic module, it must
>> + be loaded before<module>mod_heartbeat</module>.
>> +</note>
>> +
>> </summary>
>>
>> +<section id="consuming">
>> +<title>Consuming mod_heartbeat Output</title>
>> +<p>
>> + Every 1 second, this module generates a single multicast UDP
>> + packet, containing the number of busy and idle workers. The
>> + packet is a simple ASCII format, similiar to GET query parameters
>> + in HTTP.
>> +</p>
>> +
>> +<example><title>An Example Packet</title>
>> +v=1&ready=75&busy=0
>> +</example>
>> +
>> +<p>
>> + Consumers should handle new variables besides busy and ready,
>> + separated by '&', being added in the future.
>> +</p>
>> +
>> +</section>
>> +
>> +<section id="miscellaneous">
>> +<title>Miscellaneous</title>
>> +<p>The interval of 1 seconds is controlled by the HEARTBEAT_INTERVAL
>> +compile time define. This is not currently tunable at run time. To make
>> +this module send the status packet more often, you must add to the
>> +CFLAGS used to compile the module to include:</p>
>> +<example>-DHEARTBEAT_INTERVAL=3</example>
>> +<p>Would cause the broadcasts to be sent every 3 seconds.</p>
>> +</section>
"more often" than 1 second does not match the example "3 seconds" ;)
I guess more often is not possible (if resolution is seconds), so it
would be "less often"?
More important: I think this is totally wrong. The define exists, but I
couldn't find any place in the code, which is influenced by it. I
*guess* it uses the global watchdog interval configured for mod_watchdog.
>> <directivesynopsis>
>> <name>HeartbeatAddress</name>
>> -<description>Address to send heartbeat requests</description>
>> +<description>Multicast address for heartbeat packets</description>
>> <syntax>HeartbeatAddress<var>addr:port</var></syntax>
>> <default>disabled</default>
>> <contextlist><context>server config</context></contextlist>
>>
>> <usage>
>> -<p>The<directive>HeartbeatAddress</directive> directive specifies the
>> - address<module>mod_heartbeat</module> will send status information to. This
>> - address will usually corrspond to a configured<directive
>> - module="mod_heartmonitor">HeartbeatListen</directive> on a frontend
>> - proxy system.</p>
>> +<p>The<directive>HeartbeatAddress</directive> directive specifies the
>> +multicast address to which<module>mod_heartbeat</module> will send
>> +status information. This address will usually correspond to a configured
>> +<directive module="mod_heartmonitor">HeartbeatListen</directive> on a
>> +frontend proxy system.</p>
>> +<example>
>> +HeartbeatAddress 239.0.0.1:27999
>> +</example>
>> </usage>
>> </directivesynopsis>
Should we note, that Multicast needs to be enabled on both notes and
routing needs to be set up, so that the multicast packets from the
origin server can reach the proxy? On the one hand it is obvious, on the
other hand not unlikely to be the typical first problem people run into.
>> Modified: httpd/httpd/trunk/docs/manual/mod/mod_heartmonitor.xml
>> URL: http://svn.apache.org/viewvc/httpd/httpd/trunk/docs/manual/mod/mod_heartmonitor.xml?rev=1228700&r1=1228699&r2=1228700&view=diff
>> ==============================================================================
>> --- httpd/httpd/trunk/docs/manual/mod/mod_heartmonitor.xml (original)
>> +++ httpd/httpd/trunk/docs/manual/mod/mod_heartmonitor.xml Sat Jan 7 19:10:28 2012
>> @@ -20,19 +20,19 @@
>> limitations under the License.
>> -->
>>
>> -<modulesynopsis metafile="mod_heartbeat.xml.meta">
>> +<modulesynopsis metafile="mod_heartmonitor.xml.meta">
>>
>> <name>mod_heartmonitor</name>
>> <description>centralized monitor for mod_heartbeat origin servers</description>
>> <status>Experimental</status>
>> -<sourcefile>mod_heartmonitor</sourcefile>
>> +<sourcefile>mod_heartmonitor.c</sourcefile>
>> <identifier>heartmonitor_module</identifier>
>> <compatibility>Available in Apache 2.3 and later</compatibility>
>>
>> <summary>
>> <p>
>> <module>mod_heartmonitor</module> listens for server status messages generated
>> -by<module>mod_heartbeat</module> enabled servers and makes their status
>> +by<module>mod_heartbeat</module> enabled origin servers and makes their status
>> available to<module>mod_lbmethod_heartbeat</module>. This allows
>> <directive module="mod_proxy">ProxyPass</directive> to use the "heartbeat"
>> <em>lbmethod</em> inside of<directive module="mod_proxy">ProxyPass</directive>.
>> @@ -41,22 +41,34 @@ available to<module>mod_lbmethod_heartb
>> <p>This module uses the services of<module>mod_slotmem_shm</module> when
>> available instead of flat-file storage. No configuration is required to
>> use<module>mod_slotmem_shm</module>.</p>
>> +
>> +<note type="warning">
>> + To use<module>mod_heartmonitor</module>,
>> +<module>mod_status</module> and<module>mod_watchdog</module>
>> + must be either a static modules or, if a dynamic module, it must
>> + be loaded before<module>mod_heartmonitor</module>.
>> +</note>
>> +
??
>> </summary>
>>
>> <directivesynopsis>
>> <name>HeartbeatListen</name>
>> -<description>address to listen for incoming heartbeat requests</description>
>> +<description>multicast address to listen for incoming heartbeat requests</description>
>> <syntax>HeartbeatListen<var>addr:port</var></syntax>
>> <default>disabled</default>
>> <contextlist><context>server config</context></contextlist>
>>
>> <usage>
>> <p>The<directive>HeartbeatListen</directive> directive specifies the
>> - address the server will listen on for status information from
>> + multicast address on which the server will listen for status information from
>> <module>mod_heartbeat</module>-enabled servers. This
>> address will usually corrspond to a configured<directive
>> module="mod_heartbeat">HeartbeatAddress</directive> on an origin server.
>> </p>
>> +
>> +<example>
>> + HeartbeatListen 239.0.0.1:27999
>> +</example>
Same remark concerning the use of multicast as above.
>> <p> This module is inactive until this directive is used.</p>
>> </usage>
>> @@ -88,7 +100,7 @@ heartbeat requests to this server</descr
>> <p>The<directive>HeartbeatMaxServers</directive> directive specifies the
>> maximum number of servers that will be sending requests to this monitor
>> server. It is used to control the size of the shared memory allocated
>> - to store the heartbeat info.</p>
>> + to store the heartbeat info when<module>mod_slotmem_shm</module> is in use.</p>
Can this be changed using graceful restart? Only for flat file or also
for shm?
Typo: "corrspond" -> "correspond"
Additional info: it seems the data used for the load balancer is updated
about every 5 seconds (define HM_UPDATE_SEC). More precisely it seems
the heartmonitor is called by watchdog (with interval 0 seconds, but
watchdog sleep at least 100ms), then updates the data from what is had
previously read, then loops for 5 seconds reading new data and then
returns to watchdog. This is done one one thread per child, but a mutex
guarantees, that it only runs in one child at every time. Hope I'm right.
Furthermore the heartmonitor contains some additional code to handle
POST requests directed to it and reading usage data directly from the
POST body (in addition to the multicast method).
I think the current info in mod_lbmethod_heartbeat.xml is confusing. It
contains:
"This modules load balancing algorithm favors servers with more ready
(idle) capacity over time, but does not select the server with the most
ready capacity every time. Servers that have 0 active clients are
penalized, with the assumption that they are not fully initialized."
As far as I can see in the code, it randomly chooses one of the idle
origin server slots based on the last received heartbeat data. Another
equivalent formulation would be: it does a weighted balancing to the
origin servers, where the weights are proportional to the idle (ready)
slots reported with the last heartbeat message.
I couldn't find code that penalizes servers with 0 active clients.
It seems the heartbeat lb opens the data file for each request. So if
I'm right, using slotmem is highly recommended for performance reasons.
>> </usage>
>> </directivesynopsis>
>> </modulesynopsis>
>>
>> Added: httpd/httpd/trunk/docs/manual/mod/mod_watchdog.xml
>> URL: http://svn.apache.org/viewvc/httpd/httpd/trunk/docs/manual/mod/mod_watchdog.xml?rev=1228700&view=auto
>> ==============================================================================
>> --- httpd/httpd/trunk/docs/manual/mod/mod_watchdog.xml (added)
>> +++ httpd/httpd/trunk/docs/manual/mod/mod_watchdog.xml Sat Jan 7 19:10:28 2012
>> @@ -0,0 +1,60 @@
>> +<?xml version="1.0"?>
>> +<!DOCTYPE modulesynopsis SYSTEM "../style/modulesynopsis.dtd">
>> +<?xml-stylesheet type="text/xsl" href="../style/manual.en.xsl"?>
>> +
>> +<!--
>> + Licensed to the Apache Software Foundation (ASF) under one or more
>> + contributor license agreements. See the NOTICE file distributed with
>> + this work for additional information regarding copyright ownership.
>> + The ASF licenses this file to You under the Apache License, Version 2.0
>> + (the "License"); you may not use this file except in compliance with
>> + the License. You may obtain a copy of the License at
>> +
>> + http://www.apache.org/licenses/LICENSE-2.0
>> +
>> + Unless required by applicable law or agreed to in writing, software
>> + distributed under the License is distributed on an "AS IS" BASIS,
>> + WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
>> + See the License for the specific language governing permissions and
>> + limitations under the License.
>> +-->
>> +
>> +<modulesynopsis metafile="mod_watchdog.xml.meta">
>> +<name>mod_watchdog</name>
>> +<description>provides infrastructure for other modules to periodically run
>> + tasks</description>
>> +<status>Base</status>
>> +<sourcefile>mod_watchdog.c</sourcefile>
>> +<identifier>watchdog_module</identifier>
>> +<compatibility>Available in Apache 2.3 and later</compatibility>
>> +
>> +<summary>
>> +<p><module>mod_watchdog</module> defines programmatic hooks for other modules to
>> +periodically run tasks. These modules can register handlers for
>> +<module>mod_watchdog</module> hooks. Currently, the following modules in the
>> +Apache distribution use this functionality:</p>
>> +<ul>
>> +<li><module>mod_heartbeat</module></li>
>> +<li><module>mod_heartmonitor</module></li>
>> +</ul>
>> +<note type="warning">
>> +To allow a module to use<module>mod_watchdog</module> functionality,
>> +<module>mod_watchdog</module> itself must be statically linked to the server
>> +core or, if a dynamic module, be loaded before the calling module.
>> +</note>
>> +</summary>
>> +
>> +<directivesynopsis>
>> +<name>WatchdogInterval</name>
>> +<description>Watchdog interval in seconds</description>
>> +<syntax>WatchdogInterval<var>number-of-seconds</var></syntax>
>> +<default>WatchdogInterval 1</default>
>> +<contextlist><context>server config</context></contextlist>
>> +
>> +<usage>
>> +Sets the interval at which the watchdog_step hook runs. Default is to run every
>> +second.
>> +</usage>
>> +</directivesynopsis>
>> +</modulesynopsis>
>> +
We could mention, that there are two ways (and APIs) a module can use
mod_watchdog. Either synchronously called every watchdog interval
seconds, or running on a separate thread called every interval seconds,
where interval is given during the setup.
Furthermore modules can tell mod_watchdog, whether the tasks should be
run in each child independently, or coordinated by a mutex.
Regards,
Rainer
Re: Fwd: svn commit: r1228700 - in /httpd/httpd/trunk/docs: STATUS
manual/mod/mod_heartbeat.xml manual/mod/mod_heartmonitor.xml manual/mod/mod_watchdog.xml
manual/mod/mod_watchdog.xml.meta
Posted by Rainer Jung <ra...@kippdata.de>.
On 07.01.2012 20:22, Sander Temme wrote:
> Folks,
>
> I've put in some updates to the mod_heart* modules, taken from the README supplied with the modules and some perusal of the source code. I have not run these as I'm too lazy to set up the servers. Review would be appreciated, especially by the original authors (Cc), before backport to 2.4.x.
I added some comments inline, just based on reading your docs.
> Also added a doc file for mod_watchdog. Question for the docs folks: since this one is only of interest for consumption by other modules, how much documentation should we supply in the user-facing pages? I said "this module defines programmatic hooks"... do we need to define what the hook handler prototypes are? That's more like developer documentation. Thoughts?
I don't know about the history of similar decisions, but IMHO what you
wrote is good enough for 2.4.0.
>> Modified: httpd/httpd/trunk/docs/manual/mod/mod_heartbeat.xml
>> URL: http://svn.apache.org/viewvc/httpd/httpd/trunk/docs/manual/mod/mod_heartbeat.xml?rev=1228700&r1=1228699&r2=1228700&view=diff
>> ==============================================================================
>> --- httpd/httpd/trunk/docs/manual/mod/mod_heartbeat.xml (original)
>> +++ httpd/httpd/trunk/docs/manual/mod/mod_heartbeat.xml Sat Jan 7 19:10:28 2012
>> @@ -35,21 +35,66 @@ that advertises the servers current conn
>> will be running on a proxy server with<module>mod_lbmethod_heartbeat</module> loaded, which allows
>> <directive module="mod_proxy">ProxyPass</directive> to use the "heartbeat"<em>lbmethod</em> inside
>> of<directive module="mod_proxy">ProxyPass</directive>.</p>
>> +<p>
>> +<module>mod_heartbeat</module> itself is loaded on the origin server(s) that serve requests
>> + through the proxy server(s).
>> +</p>
>> +
>> +<note type="warning">
>> + To use<module>mod_heartbeat</module>,
>> +<module>mod_status</module> and<module>mod_watchdog</module>
>> + must be either a static modules or, if a dynamic module, it must
>> + be loaded before<module>mod_heartbeat</module>.
>> +</note>
>> +
>> </summary>
>>
>> +<section id="consuming">
>> +<title>Consuming mod_heartbeat Output</title>
>> +<p>
>> + Every 1 second, this module generates a single multicast UDP
>> + packet, containing the number of busy and idle workers. The
>> + packet is a simple ASCII format, similiar to GET query parameters
>> + in HTTP.
>> +</p>
>> +
>> +<example><title>An Example Packet</title>
>> +v=1&ready=75&busy=0
>> +</example>
>> +
>> +<p>
>> + Consumers should handle new variables besides busy and ready,
>> + separated by '&', being added in the future.
>> +</p>
>> +
>> +</section>
>> +
>> +<section id="miscellaneous">
>> +<title>Miscellaneous</title>
>> +<p>The interval of 1 seconds is controlled by the HEARTBEAT_INTERVAL
>> +compile time define. This is not currently tunable at run time. To make
>> +this module send the status packet more often, you must add to the
>> +CFLAGS used to compile the module to include:</p>
>> +<example>-DHEARTBEAT_INTERVAL=3</example>
>> +<p>Would cause the broadcasts to be sent every 3 seconds.</p>
>> +</section>
"more often" than 1 second does not match the example "3 seconds" ;)
I guess more often is not possible (if resolution is seconds), so it
would be "less often"?
More important: I think this is totally wrong. The define exists, but I
couldn't find any place in the code, which is influenced by it. I
*guess* it uses the global watchdog interval configured for mod_watchdog.
>> <directivesynopsis>
>> <name>HeartbeatAddress</name>
>> -<description>Address to send heartbeat requests</description>
>> +<description>Multicast address for heartbeat packets</description>
>> <syntax>HeartbeatAddress<var>addr:port</var></syntax>
>> <default>disabled</default>
>> <contextlist><context>server config</context></contextlist>
>>
>> <usage>
>> -<p>The<directive>HeartbeatAddress</directive> directive specifies the
>> - address<module>mod_heartbeat</module> will send status information to. This
>> - address will usually corrspond to a configured<directive
>> - module="mod_heartmonitor">HeartbeatListen</directive> on a frontend
>> - proxy system.</p>
>> +<p>The<directive>HeartbeatAddress</directive> directive specifies the
>> +multicast address to which<module>mod_heartbeat</module> will send
>> +status information. This address will usually correspond to a configured
>> +<directive module="mod_heartmonitor">HeartbeatListen</directive> on a
>> +frontend proxy system.</p>
>> +<example>
>> +HeartbeatAddress 239.0.0.1:27999
>> +</example>
>> </usage>
>> </directivesynopsis>
Should we note, that Multicast needs to be enabled on both notes and
routing needs to be set up, so that the multicast packets from the
origin server can reach the proxy? On the one hand it is obvious, on the
other hand not unlikely to be the typical first problem people run into.
>> Modified: httpd/httpd/trunk/docs/manual/mod/mod_heartmonitor.xml
>> URL: http://svn.apache.org/viewvc/httpd/httpd/trunk/docs/manual/mod/mod_heartmonitor.xml?rev=1228700&r1=1228699&r2=1228700&view=diff
>> ==============================================================================
>> --- httpd/httpd/trunk/docs/manual/mod/mod_heartmonitor.xml (original)
>> +++ httpd/httpd/trunk/docs/manual/mod/mod_heartmonitor.xml Sat Jan 7 19:10:28 2012
>> @@ -20,19 +20,19 @@
>> limitations under the License.
>> -->
>>
>> -<modulesynopsis metafile="mod_heartbeat.xml.meta">
>> +<modulesynopsis metafile="mod_heartmonitor.xml.meta">
>>
>> <name>mod_heartmonitor</name>
>> <description>centralized monitor for mod_heartbeat origin servers</description>
>> <status>Experimental</status>
>> -<sourcefile>mod_heartmonitor</sourcefile>
>> +<sourcefile>mod_heartmonitor.c</sourcefile>
>> <identifier>heartmonitor_module</identifier>
>> <compatibility>Available in Apache 2.3 and later</compatibility>
>>
>> <summary>
>> <p>
>> <module>mod_heartmonitor</module> listens for server status messages generated
>> -by<module>mod_heartbeat</module> enabled servers and makes their status
>> +by<module>mod_heartbeat</module> enabled origin servers and makes their status
>> available to<module>mod_lbmethod_heartbeat</module>. This allows
>> <directive module="mod_proxy">ProxyPass</directive> to use the "heartbeat"
>> <em>lbmethod</em> inside of<directive module="mod_proxy">ProxyPass</directive>.
>> @@ -41,22 +41,34 @@ available to<module>mod_lbmethod_heartb
>> <p>This module uses the services of<module>mod_slotmem_shm</module> when
>> available instead of flat-file storage. No configuration is required to
>> use<module>mod_slotmem_shm</module>.</p>
>> +
>> +<note type="warning">
>> + To use<module>mod_heartmonitor</module>,
>> +<module>mod_status</module> and<module>mod_watchdog</module>
>> + must be either a static modules or, if a dynamic module, it must
>> + be loaded before<module>mod_heartmonitor</module>.
>> +</note>
>> +
??
>> </summary>
>>
>> <directivesynopsis>
>> <name>HeartbeatListen</name>
>> -<description>address to listen for incoming heartbeat requests</description>
>> +<description>multicast address to listen for incoming heartbeat requests</description>
>> <syntax>HeartbeatListen<var>addr:port</var></syntax>
>> <default>disabled</default>
>> <contextlist><context>server config</context></contextlist>
>>
>> <usage>
>> <p>The<directive>HeartbeatListen</directive> directive specifies the
>> - address the server will listen on for status information from
>> + multicast address on which the server will listen for status information from
>> <module>mod_heartbeat</module>-enabled servers. This
>> address will usually corrspond to a configured<directive
>> module="mod_heartbeat">HeartbeatAddress</directive> on an origin server.
>> </p>
>> +
>> +<example>
>> + HeartbeatListen 239.0.0.1:27999
>> +</example>
Same remark concerning the use of multicast as above.
>> <p> This module is inactive until this directive is used.</p>
>> </usage>
>> @@ -88,7 +100,7 @@ heartbeat requests to this server</descr
>> <p>The<directive>HeartbeatMaxServers</directive> directive specifies the
>> maximum number of servers that will be sending requests to this monitor
>> server. It is used to control the size of the shared memory allocated
>> - to store the heartbeat info.</p>
>> + to store the heartbeat info when<module>mod_slotmem_shm</module> is in use.</p>
Can this be changed using graceful restart? Only for flat file or also
for shm?
Typo: "corrspond" -> "correspond"
Additional info: it seems the data used for the load balancer is updated
about every 5 seconds (define HM_UPDATE_SEC). More precisely it seems
the heartmonitor is called by watchdog (with interval 0 seconds, but
watchdog sleep at least 100ms), then updates the data from what is had
previously read, then loops for 5 seconds reading new data and then
returns to watchdog. This is done one one thread per child, but a mutex
guarantees, that it only runs in one child at every time. Hope I'm right.
Furthermore the heartmonitor contains some additional code to handle
POST requests directed to it and reading usage data directly from the
POST body (in addition to the multicast method).
I think the current info in mod_lbmethod_heartbeat.xml is confusing. It
contains:
"This modules load balancing algorithm favors servers with more ready
(idle) capacity over time, but does not select the server with the most
ready capacity every time. Servers that have 0 active clients are
penalized, with the assumption that they are not fully initialized."
As far as I can see in the code, it randomly chooses one of the idle
origin server slots based on the last received heartbeat data. Another
equivalent formulation would be: it does a weighted balancing to the
origin servers, where the weights are proportional to the idle (ready)
slots reported with the last heartbeat message.
I couldn't find code that penalizes servers with 0 active clients.
It seems the heartbeat lb opens the data file for each request. So if
I'm right, using slotmem is highly recommended for performance reasons.
>> </usage>
>> </directivesynopsis>
>> </modulesynopsis>
>>
>> Added: httpd/httpd/trunk/docs/manual/mod/mod_watchdog.xml
>> URL: http://svn.apache.org/viewvc/httpd/httpd/trunk/docs/manual/mod/mod_watchdog.xml?rev=1228700&view=auto
>> ==============================================================================
>> --- httpd/httpd/trunk/docs/manual/mod/mod_watchdog.xml (added)
>> +++ httpd/httpd/trunk/docs/manual/mod/mod_watchdog.xml Sat Jan 7 19:10:28 2012
>> @@ -0,0 +1,60 @@
>> +<?xml version="1.0"?>
>> +<!DOCTYPE modulesynopsis SYSTEM "../style/modulesynopsis.dtd">
>> +<?xml-stylesheet type="text/xsl" href="../style/manual.en.xsl"?>
>> +
>> +<!--
>> + Licensed to the Apache Software Foundation (ASF) under one or more
>> + contributor license agreements. See the NOTICE file distributed with
>> + this work for additional information regarding copyright ownership.
>> + The ASF licenses this file to You under the Apache License, Version 2.0
>> + (the "License"); you may not use this file except in compliance with
>> + the License. You may obtain a copy of the License at
>> +
>> + http://www.apache.org/licenses/LICENSE-2.0
>> +
>> + Unless required by applicable law or agreed to in writing, software
>> + distributed under the License is distributed on an "AS IS" BASIS,
>> + WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
>> + See the License for the specific language governing permissions and
>> + limitations under the License.
>> +-->
>> +
>> +<modulesynopsis metafile="mod_watchdog.xml.meta">
>> +<name>mod_watchdog</name>
>> +<description>provides infrastructure for other modules to periodically run
>> + tasks</description>
>> +<status>Base</status>
>> +<sourcefile>mod_watchdog.c</sourcefile>
>> +<identifier>watchdog_module</identifier>
>> +<compatibility>Available in Apache 2.3 and later</compatibility>
>> +
>> +<summary>
>> +<p><module>mod_watchdog</module> defines programmatic hooks for other modules to
>> +periodically run tasks. These modules can register handlers for
>> +<module>mod_watchdog</module> hooks. Currently, the following modules in the
>> +Apache distribution use this functionality:</p>
>> +<ul>
>> +<li><module>mod_heartbeat</module></li>
>> +<li><module>mod_heartmonitor</module></li>
>> +</ul>
>> +<note type="warning">
>> +To allow a module to use<module>mod_watchdog</module> functionality,
>> +<module>mod_watchdog</module> itself must be statically linked to the server
>> +core or, if a dynamic module, be loaded before the calling module.
>> +</note>
>> +</summary>
>> +
>> +<directivesynopsis>
>> +<name>WatchdogInterval</name>
>> +<description>Watchdog interval in seconds</description>
>> +<syntax>WatchdogInterval<var>number-of-seconds</var></syntax>
>> +<default>WatchdogInterval 1</default>
>> +<contextlist><context>server config</context></contextlist>
>> +
>> +<usage>
>> +Sets the interval at which the watchdog_step hook runs. Default is to run every
>> +second.
>> +</usage>
>> +</directivesynopsis>
>> +</modulesynopsis>
>> +
We could mention, that there are two ways (and APIs) a module can use
mod_watchdog. Either synchronously called every watchdog interval
seconds, or running on a separate thread called every interval seconds,
where interval is given during the setup.
Furthermore modules can tell mod_watchdog, whether the tasks should be
run in each child independently, or coordinated by a mutex.
Regards,
Rainer
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