Page MenuHomePhabricator

Make switching Redis server simpler
Open, LowPublic

Description

When the Redis server should be switched between tools-redis-1001 and tools-redis-1002, https://wikitech.wikimedia.org/wiki/Nova_Resource:Tools/Admin#Redis says:

Redis runs on two instances - tools-redis-01 and -02, and the currently active master is set via hiera on toollabs::active_redis (defaults to tools-redis-01). The other is set to be a slave of the master. Switching over can be done by:

  1. Switchover on hiera, set toollabs::active_redis to the hostname (not fqdn) of the up host
  2. Force a puppet run on the redis hosts
  3. Restart redis on the redis hosts, this resets current connections and makes master / slaves see themselves as master / slave
  4. Set the IP address for 'tools-redis.tools.eqiad.wmflabs' and 'tools-redis.eqiad.wmflabs' in hieradata/common/dnsrecursor/labsaliaser.yaml to point to the IP of the new master. This needs a puppet merge + run on the DNS hosts (labservices1001 and holmium as of now). Eventually we'd like to move this step to Horizon...

So there are two truths for "the active Redis server", one in toollabs::active_redis (set at https://wikitech.wikimedia.org/wiki/Hiera:Tools; used for /etc/hosts and setting up replication between the Redis servers), one in hieradata/common/dnsrecursor/labsaliaser.yaml (used for DNS). In addition, the documentation says that the Redis services need to be restarted (I'm not sure that this is actually necessary ATM).

Instead, the truth for "the active Redis server" should only live in hieradata/common/dnsrecursor/labsaliaser.yaml. Redis servers should check whether their IP is the same as tools-redis and consider themselves master/slave per that. They should automatically restart on changes to the replication direction.

While this requires someone with +2 on operations/puppet to switch the Redis server, these changes are rare and often done by administrators with +2.

Related Objects

Event Timeline

scfc created this task.Dec 21 2016, 2:52 AM
Restricted Application added a project: Cloud-Services. · View Herald TranscriptDec 21 2016, 2:52 AM
Restricted Application added a subscriber: Aklapper. · View Herald Transcript
scfc updated the task description. (Show Details)Dec 21 2016, 2:53 AM