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Incidents/2021-11-18 codfw ipv6 network

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document status: in-review

Summary and Metadata

The metadata is aimed at helping provide a quick snapshot of context around what happened during the incident.

Incident ID 2021-11-18 codfw ipv6 network UTC Start Timestamp: YYYY-MM-DD hh:mm:ss
Incident Task https://phabricator.wikimedia.org/T299968 UTC End Timestamp YYYY-MM-DD hh:mm:ss
People Paged <amount of people> Responder Count <amount of people>
Coordinator(s) Names - Emails Relevant Metrics / SLO(s) affected Relevant metrics

% error budget

Summary: For 8 minutes, the Codfw cluster experienced partial loss of IPv6 connectivity for upload.wikimedia.org. Thanks to Happy Eyeballs there was no visible user impact (or, at worse, a slight latency increase). The Codfw cluster generally serves Mexico and parts of the US and Canada. The upload.wikimedia.org service serves photos and other media/document files, such as displayed in Wikipedia articles.

After preemptively replacing one of codfw row B spine switch (asw-b7-codfw) for signs of disk failure, the new switch was silently discarding IPv6 traffic (through and within the switch).

As this switch was a spine, ~50% traffic toward that row (from cr2) was transiting through it.

Row B being at this time the row hosting the load-balancer in front of upload-lb.codfw, this was the most visible impact.

Monitoring triggered and the interface between asw-b7-codfw and cr2-codfw was disabled, forcing traffic through the cr1<->asw-b2-codfw link. Resolving the upload-lb issue.

Replacing the switch didn't solve the underlying IPv6 issue, showing that it was not a hardware issue. Forcing a virtual-chassis master failover solved what we think was a Junos (switch operating system) bug.

Note that at the time of the issue, our Juniper support contract was expired, preventing us from opening a JTAC case.


Impact: For 8 minutes, the Codfw cluster experienced partial loss of IPv6 connectivity for upload.wikimedia.org. Thanks to Happy Eyeballs there was no visible user impact (or, at worse, a slight latency increase). The Codfw cluster generally serves Mexico and parts of the US and Canada. The upload.wikimedia.org service serves photos and other media/document files, such as displayed in Wikipedia articles.

Documentation:

  • Original maintenance/incident task, T295118

Scorecard

Incident Engagement™  ScoreCard Score
People Were the people responding to this incident sufficiently different than the previous N incidents? (0/5pt)
Were the people who responded prepared enough to respond effectively (0/5pt)
Did fewer than 5 people get paged (0/5pt)?
Were pages routed to the correct sub-team(s)?
Were pages routed to online (working hours) engineers (0/5pt)? (score 0 if people were paged after-hours)
Process Was the incident status section actively updated during the incident? (0/1pt)
If this was a major outage noticed by the community, was the public status page updated? If the issue was internal, was the rest of the organization updated with relevant incident statuses? (0/1pt)
Is there a phabricator task for the incident? (0/1pt)
Are the documented action items assigned?  (0/1pt)
Is this a repeat of an earlier incident (-1 per prev occurrence)
Is there an open task that would prevent this incident / make mitigation easier if implemented? (0/-1p per task)
Tooling Did the people responding have trouble communicating effectively during the incident due to the existing or lack of tooling? (0/5pt)
Did existing monitoring notify the initial responders? (1pt)
Were all engineering tools required available and in service? (0/5pt)
Was there a runbook for all known issues present? (0/5pt)
Total Score

Actionables

  • Icinga check for ipv6 host reachability, T163996