Canary

canary in Wikimedia technology may refer to:

• The debug servers, e. g. mwdebug1002, are sometimes called canaries. scap backport will deploy changes to them first and then wait for confirmation before deploying them to the rest of production.
• Scap has the notion of canary hosts: when deploying a change, it will first deploy it to a subset of servers, then pause for a bit and check their error rate. If enough canary servers experience a significantly higher error rate, the deployment is automatically aborted (though the canary servers continue to serve traffic with the deployed code).
• group0 wikis are sometimes called canary wikis. Problems with a new MediaWiki version may be discovered there before they start affecting the bigger wikis.
• canary events. These are artificially injected into WMF Event Platform streams to differentiate between empty streams and broken streams.

(All three meanings refer to the idiom of a canary in a coal mine.)