Incident documentation/2021-09-13 cirrussearch restart

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document status: draft


Applying a change to our cirrus elasticsearch systemd unit triggered puppet to automatically restart the associated elasticsearch services. Sufficient number of hosts (6) were having puppet-agent ran simultaneously to drop the cluster into yellow and then red status; the large bandwidth/resources required to reschedule and assign shards when the respective elasticsearch services came back up on each host likely contributed to general cluster instability leading to a cascading failure scenario.

Elasticsearch itself did its job in coming back and immediately recovering shards, but given the volume of hosts restarted, it took about 40 minutes for the impact to users to become largely invisible, and 2 hours and 5 minutes for a full recovery of the backend (i.e. green cluster status).

16:18 Puppet change touching cirrus elasticsearch systemd units merged:

16:23 operator runs puppet manually on elastic2052, confirmed elasticsearch service came back up properly

16:25 operator runs puppet on rest of fleet, 6 hosts at a time: sudo cumin -b 6 'P{elastic*}' 'sudo run-puppet-agent'

16:29 PROBLEM - PyBal backends health check on lvs1015 is CRITICAL: PYBAL CRITICAL - CRITICAL - search-psi-https_9643: Servers elastic1059.eqiad.wmnet, elastic1049.eqiad.wmnet, elastic1044.eqiad.wmnet, elastic1048.eqiad.wmnet, elastic1052.eqiad.wmnet, elastic1047.eqiad.wmnet, elastic1067.eqiad.wmnet, elastic1035.eqiad.wmnet, elastic1045.eqiad.wmnet are marked down but pooled

16:31 ElasticSearch health check for shards on 9243 on search.svc.codfw.wmnet is CRITICAL. At the same time, production-search-codfw has dropped into red cluster status

17:09 enwiki searches begin to work again (presumably due to recovery of the associated enwiki shards). User-visible impact decreases.

18:?? codfw enters green cluster status (full recovery)

18:?? eqiad enters green cluster status (full recovery)

18:30 MediaWiki api_appserver latency returns to normal levels

18:34 PoolCounter stops rejecting requests, user-visible impact ends.

The api_appserver cluster saw higher latency during the outage.

Impact: Search requests on (and likely other wikis as well) failed with "An error has occurred while searching: Search is currently too busy. Please try again later."; this outage persisted for about 2 hours, from 16:29 until 18:34. Until the cluster recovered 100%, the MediaWiki api_appserver cluster saw higher latency because of slower search requests.



  • task T290902 Iron out procedure to roll out cirrus/elasticsearch changes involving [implicitly via puppet or explicitly] service restarts