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Canary

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Revision as of 13:37, 16 August 2021 by imported>Lucas Werkmeister (WMDE) (clarify what happens if scap canary check fails: the code is *not* automatically rolled back to the last good version)
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The term “canary” can describe different things:

  • 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.