Incidents/2023-05-25 eqiad/LVS

== Summary ==
…
During scap deploys one of the LVS servers in eqiad was taken down which resulted in multiple servers being depooled making eqiad unable so serve traffic.
==Timeline==
All times in UTC.
*Scap runs at 13:52, 14:08, 14:10
*14:04 PyBal disabled on lvs1019 as part of maintenance but a deploy was ongoing OUTAGE BEGINS
*14:05 PROBLEM - PyBal backends health check on lvs1019 is CRITICAL: PYBAL CRITICAL - Bad Response from pybal: 500 Cant connect to localhost:9090 (Connection refused) https://wikitech.wikimedia.org/wiki/PyBal
*14:08 <icinga-wm> PROBLEM - PyBal backends health check on lvs1020 is CRITICAL: PYBAL CRITICAL - CRITICAL - appservers-https_443: Servers mw1418.eqiad.wmnet, mw1417.eqiad.wmnet, mw1416.eqiad.wmnet, mw1415.eqiad.wmnet, mw1414.eqiad.wmnet are marked down but pooled: parsoid-php_443: Servers parse1017.eqiad.wmnet, parse1011.eqiad.wmnet are marked down but pooled: api-https_443: Servers mw1447.eqiad.wmnet, mw1448.eqiad.wmnet, mw1449.eqiad.wmnet, mw1450.eqiad.wmnet marked down but pooled https://wikitech.wikimedia.org/wiki/PyBal
*14:09: PyBal re-started on lvs1019
*14:14 bblack started repooling parsoid in
*14:17  Incident opened.  Janis becomes IC.
*14:21 appservers and api_appservers repooled
*14:22 jobrunners and videoscalers repooled
*14:25 recoveries coming in OUTAGE ENDS
*14:42 still elevated latencies on api_appservers, might be unrelated as there is a spike of read traffic on s7
*14:58 s7 query throughput is high due to db maintenance, most likely unrelated
*14:58 api_appserver latency trending down
*15:08] <jinxer-wm> (MediaWikiLatencyExceeded) resolved: Average latency high: ...
==Detection==
The issue was detected immediately by SRE doing maintenance work. Multiple alerts as well as pages immediately followed.
==Conclusions ==
===What went well?===
* Automated alerting detected the issue quickly
===What went poorly?===
*We did not manage to avoid this happening again although we already knew about LVS downtime during scap deploys being an issue
===Where did we get lucky?===
* Remediation of the outage was quick due to its root cause already being known, see Incidents/2023-04-17 eqiad/LVS
==Links to relevant documentation==
* Incidents/2023-04-17 eqiad/LVS
* https://phabricator.wikimedia.org/T334703
* https://phabricator.wikimedia.org/T337497
==Actionables==
* https://phabricator.wikimedia.org/T334703
==Scorecard==
Incident Engagement ScoreCard
 	Question 	Answer
(yes/no)	Notes
People 	Were the people responding to this incident sufficiently different than the previous five incidents? 	no 	
People 	Were the people who responded prepared enough to respond effectively 	yes	
People 	Were fewer than five people paged? 	yes	
People 	Were pages routed to the correct sub-team(s)? 	no 	
People 	Were pages routed to online (business hours) engineers?  Answer “no” if engineers were paged after business hours.	yes	
Process 	Was the "Incident status" section atop the Google Doc kept up-to-date during the incident? 	yes	
Process 	Was a public wikimediastatus.net entry created? 	yes	
Process 	Is there a phabricator task for the incident? 	yes	
Process 	Are the documented action items assigned? 	yes	
Process 	Is this incident sufficiently different from earlier incidents so as not to be a repeat occurrence? 	no 	Same issue as Incidents/2023-04-17 eqiad/LVS
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 	
Tooling 	Were the people responding able to communicate effectively during the incident with the existing tooling? 	yes	
Tooling 	Did existing monitoring notify the initial responders? 	yes	
Tooling 	Were the engineering tools that were to be used during the incident, available and in service? 	yes	
Tooling 	Were the steps taken to mitigate guided by an existing runbook? 	no 	
Total score (count of all “yes” answers above)	Total score (count of all “yes” answers above) 	10