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Incidents/2023-08-09 mw-on-k8s outage due to wrong tls cert

From Wikitech

document status: draft


Incident metadata (see Incident Scorecard)
Incident ID 2023-08-09 mw-on-k8s outage due to wrong tls cert Start 2023-08-09 11:41
Task End 2023-08-09 12:16
People paged 2 Responder count jynus, jayme
Coordinators - Affected metrics/SLOs Mediawiki web and api availability
Impact For approximately 30 minutes 1% of traffic received errors (120 requests/s)

A change to the global k8s defaults was merged that made the next mediawiki on kubernetes deployment pick up a wrong certificate for TLS termination.


All times in UTC.


The issue was detected by a page:

(ProbeDown) firing: (6) Service mw-api-ext:4447 has failed probes (http_mw-api-ext_ip4)
(ProbeDown) firing: Service mw-api-int:4446 has failed probes (http_mw-api-int_ip4)

There was also secondary failures:

[12:51] <jinxer-wm> (KubernetesAPILatency) resolved: (4) High Kubernetes API latency
[12:02] <icinga-wm> PROBLEM - Check unit status of httpbb_kubernetes_mw-api-int_hourly on cumin2002 is CRITICAL


What went well?

  • The root of the problem could be detected quickly because the person that issued the breaking change was a responder

What went poorly?

  • The root cause should have been visible CI (unfortunately not in the CI of the repo the change was made in; hieradata vs. deployment-charts)

Where did we get lucky?

  • Only 1% of traffic is routed to k8s currently, so there was only limited impact

Links to relevant documentation


  • Because of the low traffic (relatively small amount of errors) it took some time to pin this to k8s- does that need some actionables, or will it resolve itself as k8s becomes the majority of requests?
  • Review if some deployment procedures/testing should be strengthen (e.g. surprising changes on next deployment, canary deployment for k8s, etc)
  • Some metrics become unavailable or unhealthy during deployment- could something be done about that (either for the metrics or mitigation of deployment impact)
  • Should depooling k8s have been done earlier?


Incident Engagement ScoreCard
Question Answer


People Were the people responding to this incident sufficiently different than the previous five incidents? yes
Were the people who responded prepared enough to respond effectively yes
Were fewer than five people paged? yes
Were pages routed to the correct sub-team(s)? no
Were pages routed to online (business hours) engineers?  Answer “no” if engineers were paged after business hours. yes
Process Was the "Incident status" section atop the Google Doc kept up-to-date during the incident? no no google doc
Was a public wikimediastatus.net entry created? no
Is there a phabricator task for the incident? no
Are the documented action items assigned? yes no action items
Is this incident sufficiently different from earlier incidents so as not to be a repeat occurrence? yes
Tooling To the best of your knowledge was the open task queue free of any tasks that would have prevented this incident? Answer “no” if there are

open tasks that would prevent this incident or make mitigation easier if implemented.

Were the people responding able to communicate effectively during the incident with the existing tooling? yes
Did existing monitoring notify the initial responders? yes
Were the engineering tools that were to be used during the incident, available and in service? yes
Were the steps taken to mitigate guided by an existing runbook? no
Total score (count of all “yes” answers above)