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Switch Datacenter/MemcachedRedisSessions

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This page describes the procedure to switch over safely the redis/memcached cluster in the process of switching mediawiki.

When in need to switch over mediawiki, the replication flow of redis must change.

The simplest and safest way to do this now is as follows:

  1. Stop puppet on all hosts of this cluster cumin 'A:memcached' 'puppet agent --disable "pre-switchover"'
  2. Switch the puppet configuration so that the primary datacenter is now the new one
  3. Run puppet on the machines in the new master datacenter (so that the replica stops flowing)
  4. Re-enable puppet in the whole cluster; the machines in the other datacenters will eventually catch up