Ops notifications
The operations team provides notification of maintenance or upgrades being done, emergency outages, and day to day work. Below is a summary of the different means in use by ops.
IRC
Primary channel: #wikimedia-operations at irc.freenode.net
Use: day to day work and discussions go on here. Updates to the sysadmin log are done from here.
Secondary channel: #wikimedia-tech at irc.freenode.net
Use: during an outage, someone is usually monitoring and providing updates to this channel, while watching for reports of problems.
Other:
For sensitive matters that involve possible security or privacy issues, discussion is carried out elsewhere, for obvious reasons.
Server Admin Log (SAL)
Use: powercycling machines, restart of services, upgrades or configuration changes etc. are logged here. During long outages brief status updates will be provided here as well.
Everything posted to the Server Admin Log is also posted to twitter [1], account @wikimediatech.
Wiki
Outage post-mortems are published on-wiki as incident reports.
Phabricator
When bugs involving operational issues are opened, followup will be done here (publicly available [2])
There is no single public email mechanism currently in use for updates during site outages or after recovery. (Should there be, or do the above cover us?)
Gerrit
You can look at Gerrit changes and see what has been merged in ops-related projects, f.e. operations/puppet and other operations/* repositories.