Incidents/2022-05-21 varnish cache busting

From Wikitech

document status: final


Incident metadata (see Incident Scorecard)
Incident ID 2022-05-21 varnish cache busting Start 2022-05-21 19:01:00
Task T308940 End 2022-05-21 19:03:00
People paged 5 Responder count 7
Coordinators dzahn Affected metrics/SLOs
Impact For 2 minutes, all wikis and services served by our CDN were unavailable to all users.

A flood of API traffic from an AWS instance caused caching servers to be overloaded. Services behind our caching layer were up, but not reachable during this time.



Incident Engagement™ ScoreCard
Question Answer


People Were the people responding to this incident sufficiently different than the previous five incidents?
Were the people who responded prepared enough to respond effectively
Were fewer than five people paged?
Were pages routed to the correct sub-team(s)?
Were pages routed to online (business hours) engineers? Answer “no” if engineers were paged after business hours.
Process Was the incident status section actively updated during the incident?
Was the public status page updated?
Is there a phabricator task for the incident?
Are the documented action items assigned?
Is this incident sufficiently different from earlier incidents so as not to be a repeat occurrence?
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?
Did existing monitoring notify the initial responders?
Were all engineering tools required available and in service?
Was there a runbook for all known issues present?
Total score (count of all “yes” answers above)