Added the infra SOPs ported to asciidoc.

modules/sysadmin_guide/pages/memcached.adoc

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+= Memcached Infrastructure SOP
+
+Our memcached setup is currently only used for wiki sessions. With
+mediawiki, sessions stored in files over NFS or in the DB are very slow.
+Memcached is a non-blocking solution for our session storage.
+
+== Contents
+
+[arabic]
+. Contact Information
+. Checking Status
+. Flushing Memcached
+. Restarting Memcached
+. Configuring Memcached
+
+== Contact Information
+
+Owner::
+  Fedora Infrastructure Team
+Contact::
+  #fedora-admin, sysadmin-main, sysadmin-web groups
+Location::
+  PHX
+Servers::
+  memcached03, memcached04
+Purpose::
+  Provide caching for Fedora web applications.
+
+== Checking Status
+
+Our memcached instances are currently firewalled to only allow access
+from wiki application servers. To check the status of an instance, use:
+
+....
+echo stats | nc memcached0{3,4} 11211
+....
+
+from an allowed host.
+
+== Flushing Memcached
+
+Sometimes, wrong contents get cached, and the cache should be flushed.
+To do this, use:
+
+....
+echo flush_all | nc memcached0{3,4} 11211
+....
+
+from an allowed host.
+
+== Restarting Memcached
+
+Note that restarting an memcached instance will drop all sessions stored
+on that instance. As mediawiki uses hashing to distribute sessions
+across multiple instances, restarting one out of two instances will
+result in about half of the total sessions being dropped.
+
+To restart memcached:
+
+....
+sudo /etc/init.d/memcached restart
+....
+
+== Configuring Memcached
+
+Memcached is currently setup as a role in the ansible git repo. The main
+two tunables are the MAXCONN (the maximum number of concurrent
+connections) and CACHESIZE (the amount memory to use for storage). These
+variables can be set through $memcached_maxconn and $memcached_cachesize
+in ansible. Additionally, other options (as described in the memcached
+manpage) can be set via $memcached_options.