Hi all,

You may have heard already that, like last year, we are planning to switch our active datacenter from eqiad to codfw in the week of April 17th and back to eqiad two weeks later, on the week of May 1st. We do this periodically in order to exercise our ability to run from the backup site in case of a disaster, as well as our ability to switch seamlessly to it with little user impact.

Switching will be a gradual, multi-step process, the most visible step of which will be the switch of MediaWiki application servers and associated data stores. This will happen on April 19th (eqiad->codfw) and May 3rd (codfw->eqiad), both at 14:00 UTC. During those windows, the sites will be placed into read-only mode, for a period that we estimate to last approximately 20 to 30 minutes.

Furthermore, the deployment train will freeze for the weeks of April 17th and May 1st[1], but operate normally on the week of April 24th, in order to exercise our ability to deploy code while operating from the backup datacenter.

1: https://wikitech.wikimedia.org/wiki/Deployments

Compared to last year we have improved our processes considerably[2], in particular by making more services operate in an active/active manner, as well as by working on an automation and orchestration framework[3] to perform parallel executions across the fleet. The core of the MediaWiki switchover will be performed semi-automatically using a new software[4] that will execute all the necessary commands in sequence with little human involvement, and thus lowering the risk of introducing errors and delays.

2: https://wikitech.wikimedia.org/wiki/Switch_Datacenter 3: https://github.com/wikimedia/cumin 4: https://github.com/wikimedia/operations-switchdc

Improving and automating our processes means that we're not going to be following the exact same steps as last year. Because of that, and because of other changes introduced in our environment over the course of the year, there is a possibility of errors creeping into the process. We'll certainly try to fix any issues that arise during those weeks and we'd like to ask everyone to be on high-alert and vigilant.

To report any issues, please use one of the following channels:

1. File a Phabricator issue with project #codfw-rollout 2. Report issues on IRC: Freenode channel #wikimedia-tech (if urgent, or during the migration) 3. Send an e-mail to the Operations list: ops@lists.wikimedia.org (any time)

Thanks, Faidon -- Faidon Liambotis Principal Operations Engineer Acting Director of Technical Operations Wikimedia Foundation