Hello teams!
After some discussion with David, we realised that Cirrus / Elasticsearch switch is already more automated than we realised. Cirrus is configured to talk the local Elasticsearch cluster. So if we start serving traffic for Mediawiki from codfw, those mediawiki instances should contact the Elasticsearch codfw cluster.
We do have the ability to change that configuration and for the use of a specific cluster. That's what we did during the previous datacenter switch, and what we already do for some maintenance operations (yes, major upgrades of Elasticsearch do require downtime, so we use codfw during those upgrades).
Since we have already tested a manual DC switch quite a few times, it is time to check if this automatic switch is working as it should. The only downside is that it increases the number of moving parts during the Mediawiki switch.
On a last note, lots of thanks and praise to David and Erik who did think ahead much more than I did and implemented those nice features!
Have fun!
Guillaume