Canary

canary in Wikimedia technology may refer to:

• The debug servers, e. g. mwdebug1002, are sometimes called canaries. Changes are often deployed to them via scap pull before deploying them everywhere with scap sync.
• 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.