document status: draft
|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
|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.
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.
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.
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".
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
- 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)
|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.
|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?
|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 the engineering tools that were to be used during the incident, available and in service?
|Were the steps taken to mitigate guided by an existing runbook?
|Total score (count of all “yes” answers above)