Canary

canary in Wikimedia technology may refer to:

• The debug servers 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.
• cloudvirt-canary Cloud VPS project, running a test VM on each Cloud VPS hypervisor.
• Edge uniques/Canary, documentation that can be used to verify what Wikimedia Foundation does with the Edge Unique cookie.

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