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{{See|See also '''[[Application servers/Runbook]]''' for how to perform common tasks, or diagnose issues.}}
{{See|See also '''[[Application servers/Runbook]]''' for how to perform common tasks, or diagnose issues.}}


The '''Application servers''' (or '''app servers''') are the several hundred Apache servers that run the [[MediaWiki]] backend software (written in PHP).
The '''Application servers''' (or '''app servers''') are the several hundred Apache servers that run [[MediaWiki]] (PHP application).
 
{{TOC|align=right}}


==Service==
==Service==
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==Architecture==
==Architecture==
[[File:WMF_infrastructure_2022.png|thumb|400px|Each appserver cluster and their role.]]
{{See also|MediaWiki at WMF|HTTP timeouts#App servers}}
{{See also|MediaWiki at WMF|HTTP timeouts#App servers}}


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Apache access logs are mostly disabled. Statistics are drawn from [[Varnish]] front ends instead.
Apache access logs are mostly disabled. Statistics are drawn from [[Varnish]] front ends instead.


==Apache setup checklist==
==Update our PHP packages==
 
We use custom PHP packages, which are co-installable and more recent that what is shipped in the underlying Debian releases. If you want to add/update a patch you can do the following:


* Follow the [[Automated installation]] instructions for the base install
* On an existing app server obtain the source with "apt-get source php7.4"
* Run the following on the server:
* Copy the source files (*debian.tar.xz, *dsc, *orig.tar.xz(.asc)) to build2001.codfw.wmnet
:* <tt>apt-get update && apt-get dist-upgrade -y && apt-get install wikimedia-task-appserver && reboot && exit </tt>
* Unpack the souce with "dpkg-source -x $DSCFILE"
* Wait for the server to come back online, ensure it starts apache correctly
* Make the modification within the source tree (e.g. applying a local patch or a backport from upstream)
** <tt>echo 'GET /' | nc localhost 80</tt> or any of the number of tests listed below
* Run "dpkg-source --commit" to record your changes in a debian/patches/foo patch file (debian/patches/series is automatically amended)
* If the server is part of the memcached group, follow instructions on [[Memcached]]
* Bump the changelog with "dch -i" (which spawns an editor)
* If the server is new, you will need to do the following:
* Finally build the updated package with "PHP74=yes DIST=buster-wikimedia pdebuild"
:* Login to the LVS server for apaches (lvs3 as of 2009-02-13) and add the new servers to /etc/pybal/apaches
* Test the resulting build (and if all is fine, import to apt.wikimedia.org)
* If the server is not new do the following:
:* Ensure the server is now enabled in pybal on the LVS server in the file /etc/pybal/apaches
* You will need to add the server to [[DSH]] groups if new, or check if they are commented, if the server is not new:
:* Add/Uncomment the host to /usr/local/dsh/node_groups/apaches and mediawiki-installation, as well as any other groups needed
:* Reload nagios to accept the changes to the node groups:
::* <tt>cd /home/wikipedia/conf/nagios && ./sync </tt>
* Verify that the server is tacking traffic and doing work
:* <tt>ipvsadm -L | grep SERVERNAME </tt>
:* traffic logs?


== Hardware repair ==
== Hardware repair ==

Latest revision as of 00:18, 27 September 2022

The Application servers (or app servers) are the several hundred Apache servers that run MediaWiki (PHP application).

Service

Puppet roles:

  • mediawiki::appserver, mediawiki::canary_appserver
  • mediawiki::appserver::api, mediawiki::appserver::canary_api
  • mediawiki::maintenance
  • mediawiki::jobrunner

Relevant puppet classes:

Architecture

Each appserver cluster and their role.

The application servers are load-balanced via LVS. Connections between our CDN (HTTP cache proxies) and app servers are encrypted with TLS, which is terminated locally on the app server using Envoy. Envoy then hands the request off to the local Apache.

Apache is in charge of handling redirects, rewrite rules, and determining the document root. It then uses php-fpm to invoke the MediaWiki software.

The Apache MPM we use is mod_worker, which decides how php-fpm processes are spawned.

Logging

Apache errors are logged to /srv/mw-log/apache2.log on mwlog1001.

Apache access logs are mostly disabled. Statistics are drawn from Varnish front ends instead.

Update our PHP packages

We use custom PHP packages, which are co-installable and more recent that what is shipped in the underlying Debian releases. If you want to add/update a patch you can do the following:

  • On an existing app server obtain the source with "apt-get source php7.4"
  • Copy the source files (*debian.tar.xz, *dsc, *orig.tar.xz(.asc)) to build2001.codfw.wmnet
  • Unpack the souce with "dpkg-source -x $DSCFILE"
  • Make the modification within the source tree (e.g. applying a local patch or a backport from upstream)
  • Run "dpkg-source --commit" to record your changes in a debian/patches/foo patch file (debian/patches/series is automatically amended)
  • Bump the changelog with "dch -i" (which spawns an editor)
  • Finally build the updated package with "PHP74=yes DIST=buster-wikimedia pdebuild"
  • Test the resulting build (and if all is fine, import to apt.wikimedia.org)

Hardware repair

When taking down application servers (running mediawiki) for things like disk replacement or other hardware repair, _do not forget to_:

  • before: remove from dsh group

These are in puppet, operations/puppet repo, in modules/dsh/files/group. The important one for Mediawiki sync is "mediawiki-installation".

  • before: de-pool in pybal
  • TODO: Document what to do if it's a scap proxy (see hieradata/common/dsh/config.yaml)

See pybal. You can just grep for the server name and set 'enabled': False and save.

  • before: check nobody is scapping right now (best: announce with a !log line in IRC)

This is an IRC thing on libera.chat in #wikimedia-dev connect/#wikimedia-tech connect/#wikimedia-operations connect

  • during: acknowledge Icinga monitoring checks (best: with related ticket number as comment)

Do this by logging in via browser on icinga.wikimedia.org. search for the hostname, check all services and use the "acknowledge" option. You'll see the IRC bots outputting this as well and they will stop repeating things over and over in the channels.

  • after: re-add to dsh groups

Revert the above.

  • after: re-pool in pybal

Revert the above.

See also