Incidents/2022-11-15 asw1-eqsin

From Wikitech

document status: draft

Summary

Incident metadata (see Incident Scorecard)
Incident ID 2022-11-15 asw1-eqsin Start 2022-11-15 04:51:00
Task T323094 End 2022-11-15 04:56:00
People paged 0 Responder count
Coordinators 0 Affected metrics/SLOs No relevant SLOs exist - 5xx errors graph shows the impact https://grafana.wikimedia.org/d/-K8NgsUnz/home?orgId=1&from=1668487382007&to=1668488908178&viewPanel=8
Impact For about 5min, users in the APAC region (using eqsin) could have been served 5xx errors instead of the requested page.


Connecting a new server to our eqsin top of rack switches triggered a Juniper bug which caused one of its processes to be killed and interrupting traffic transiting through the switch. This event caused also a Virtual-Chassis master switchover extending the outage. The process got automatically re-started and the situation stabilized by itself in about 5min.

Timeline

Write a step by step outline of what happened to cause the incident, and how it was remedied. Include the lead-up to the incident, and any epilogue.

Consider including a graphs of the error rate or other surrogate.

Link to a specific offset in SAL using the SAL tool at https://sal.toolforge.org/ (example)

All times in UTC.

  • 04:51 (TODO) OUTAGE BEGINS
  • 00:04 (Something something)
  • 00:06 (Voila) OUTAGE ENDS
  • 00:15 (post-outage cleanup finished)

TODO: Clearly indicate when the user-visible outage began and ended.

Detection

Write how the issue was first detected. Was automated monitoring first to detect it? Or a human reporting an error?

Copy the relevant alerts that fired in this section.

Did the appropriate alert(s) fire? Was the alert volume manageable? Did they point to the problem with as much accuracy as possible?

TODO: If human only, an actionable should probably be to "add alerting".

Conclusions

OPTIONAL: General conclusions (bullet points or narrative)

What went well?

  • The situation stabilized by itself
  • Juniper was able to match the crash to a known bug (even though our code version is not supposed to be vulnerable to this bug)
  • automated monitoring detected the incident

What went poorly?

  • Nobody was paged despite the outage to be user impacting to be verified
  • Nobody present during the outage opened a task documenting what happened
  • Such improbable bug

Where did we get lucky?

Links to relevant documentation

Actionables

  • Upgrade POPs asw to Junos 21 - https://phabricator.wikimedia.org/T316532
  • We're phasing out virtual chassis in the new POP network designs (cf. drmrs). Even though such bugs might always be a possibility, the new design is more resilient (each switch is independent)

Scorecard

Incident Engagement ScoreCard
Question Answer

(yes/no)

Notes
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 no
Were fewer than five people paged? no no pages
Were pages routed to the correct sub-team(s)? no no pages
Were pages routed to online (business hours) engineers?  Answer “no” if engineers were paged after business hours. no no pages
Process Was the incident status section actively updated during the incident? no
Was the public status page updated? no
Is there a phabricator task for the incident? yes
Are the documented action items assigned? yes
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.

no
Were the people responding able to communicate effectively during the incident with the existing tooling? no
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 auto-resolved
Total score (count of all “yes” answers above)
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