Incidents/2023-11-15 esams unreachable

document status: in-review

Summary

Incident metadata (see Incident Scorecard)
Incident ID	2023-11-15 esams unreachable	Start	2023-11-15T14:04:10
Task		End	2023-11-15T14:21
People paged	batphone	Responder count	8
Coordinators	fabfur	Affected metrics/SLOs
Impact	ESAMS DC was unreachable by users

ESAMS DC was unreachable by users. Globally, we experienced a request drop from ~150k req/s to ~91k req/s as outlined in the Grafana dashboard. Users that were trying to reach Amsterdam DC experienced network errors and delays.

The incident doc still mentioned "We’re still investigating why some Grafana panels shows ~1hr of requests drop instead of ~10m (the actual incident duration)"

Timeline

14:03 <XioNoX> !log reboot fpc0 on cr1-esams - T346779 (SAL)
14:04 <XioNoX> I restarted the linecard on the wrong router… Outage starts
14:05 Start receiving alerts, e.g. <+icinga-wm> PROBLEM - Host ncredir3003 is DOWN: PING CRITICAL - Packet loss
14:06 <vgutierrez> let's depool esams?
14:07 <jynus> vgutierrez: it is recovering now
14:07 <XioNoX> looks like it's back faster than a depool is needed
14:08 <vgutierrez> I can't reach text-lb.esams.wikimedia.org from here FWIW
14:08 depool esams https://gerrit.wikimedia.org/r/c/operations/dns/+/974537/
14:08 DEPOOL FAILED due to authends-update issues
14:09 <+icinga-wm> started to see recoveries RECOVERY
14:09 <sukhe> /tmp/dns-check.rudydea2/zones/netbox/4.64.10.in-addr.arpa
14:09 <sukhe> we need to fix this to fix authdns-update
14:10 <topranks> let's just merge https://gerrit.wikimedia.org/r/c/operations/dns/+/974534
??:?? <XioNoX> text-lb is reachable again
14:11 <jynus> NEL is still high
14:16 marostegui updates the status page
14:17 <jynus> http traffic volume is still elevated, though
14:18 <jynus> others parameters look back to normal, including NEL timeouts
14:21 <+jinxer-wm> (NELHigh) resolved: (2) Elevated Network Error Logging events Outage ends
14:25 Updated status page to monitoring
14:26 Incident opened; fabfur becomes IC.
14:35 Status page set to resolved

Detection

The outage was detected by an SRE shortly after an accidental change. Fired alerts confirmed the outage as well:

<+icinga-wm> PROBLEM - Host ncredir3003 is DOWN: PING CRITICAL - Packet loss

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

Conclusions

OPTIONAL: General conclusions (bullet points or narrative)

What went well?

…

OPTIONAL: (Use bullet points) for example: automated monitoring detected the incident, outage was root-caused quickly, etc

What went poorly?

…

OPTIONAL: (Use bullet points) for example: documentation on the affected service was unhelpful, communication difficulties, etc

Where did we get lucky?

…

OPTIONAL: (Use bullet points) for example: user's error report was exceptionally detailed, incident occurred when the most people were online to assist, etc

Links to relevant documentation

Depooling servers

Actionables

…

Create a list of action items that will help prevent this from happening again as much as possible. Link to or create a Phabricator task for every step.

Add the #Sustainability (Incident Followup) and the #SRE-OnFire Phabricator tag to these tasks.

Scorecard

Incident Engagement ScoreCard
	Question	Answer (yes/no)	Notes
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	yes
	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 atop the Google Doc kept up-to-date during the incident?
	Was a public wikimediastatus.net entry created?	yes	Status page entry
	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.	no
	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?	yes	Relevant runbook
Total score (count of all “yes” answers above)