Incidents/2022-05-25 de.wikipedia.org

==Summary==
An increase in POST requests to de.wikipedia.org caused an increase in load on one of the DB servers resulting in an increase in 503 responses and increased response time
==Timeline==
All times in UTC.
*20:04 OUTAGE BEGINS
*20:04 Received page "Service text-https:443 has failed probes"
*20:08 rzl starts investigation
*20:08 Received page "(FrontendUnavailable) firing: HAProxy (cache_text) has reduced HTTP availability"
*20:08 rzl asked cjming to halt deploying
*20:09 Recived page "(FrontendUnavailable) firing: varnish-text has reduced HTTP availability"
*20:09 jbond takes IC 
*20:10 < rzl> looks like a spike of DB queries to s5 that saturated php-fpm workers, seems like it's already cleared
*20:11 Received recovery "RECOVERY - High average GET latency for mw requests on appserver"
*20:11 < cwhite> Lots of POST to https://de.wikipedia.org
*20:12 < rzl> s5 did see a traffic spike but recovered, still digging
*20:13 Received recovery "resolved: (8) Service text-https:443 has failed probes"
*20:13 Received recovery "resolved: HAProxy (cache_text) has reduced HTTP availability"
*20:14 Received recovery "resolved: varnish-text has reduced HTTP availability"
*20:14 OUTAGE ENDS
*20:14 < cwhite> 2217 unique ips (according to logstash)
*20:18 < bblack> identified traffic as "a bunch of dewiki root URLs"
*20:22 < _joe_> php slowlogs mostly showed query() or curl_exec()
*20:30 < _joe_> someone was calling radompage repeatedly?
*20:31 <rzl> looks like it was all appservers pretty equally
*20:40 Discuss remediation strategy
*20:48 Incident officially closed
*20:51 < rzl> gave cjming all clear to continue with deploy
*21:29 requestctl rule put in place
==Detection==
Error was detected by alert manager monitoring
20:08 <+jinxer-wm> (ProbeDown) firing: (8) Service text-https:443 has failed probes (http_text-https_ip4) #page - https://wikitech.wikimedia.org/wiki/Network_monitoring#ProbeDown -
https://grafana.wikimedia.org/d/O0nHhdhnz/network-probes-overview?var-job=probes/service&var-module=http - https://alerts.wikimedia.org/?q=alertname%3DProbeDown
20:08 <+jinxer-wm> (FrontendUnavailable) firing: HAProxy (cache_text) has reduced HTTP availability #page - TODO - https://grafana.wikimedia.org/d/000000479/frontend-traffic?viewPanel=13 - https://alerts.wikimedia.org/?q=alertname%3DFrontendUnavailable
20:09 <+jinxer-wm> (FrontendUnavailable) firing: varnish-text has reduced HTTP availability #page - https://wikitech.wikimedia.org/wiki/Varnish#Diagnosing_Varnish_alerts - https://grafana.wikimedia.org/d/000000479/frontend-traffic?viewPanel=3 - https://alerts.wikimedia.org/?q=alertname%3DFrontendUnavailable
==Conclusions==
Understanding of legitimate backed traffic would enable us to better sanitize bad traffic at the front end
===What went well?===
* automated monitoring detected the incident
* Had a good amount of incident responders
===What went poorly?===
* Was difficult to get a signature of the post traffic
===Where did we get lucky?===
* Incident ended quickly on its own
===How many people were involved in the remediation?===
* SREs
==Links to relevant documentation==
* Grafana: Appservers RED
==Actionables==
*T309147 any POST that doesn't go to /w/*.php or /wiki/.* should become a 301 to the same url
*T309186 Created sampled log of post data
*T310009 Make it easier to create a new requestctl object
==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	
People 	Were the people who responded prepared enough to respond effectively 	yes	
People 	Were fewer than five people paged? 	no 	
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.	no 	
Process 	Was the incident status section actively updated during the incident? 	yes	
Process 	Was the public status page updated? 	no 	
Process 	Is there a phabricator task for the incident? 	yes	(created retrospectively)
Process 	Are the documented action items assigned? 	 	
Process 	Is this incident sufficiently different from earlier incidents so as not to be a repeat occurrence? 	no 	(similar to "2022-05-20 Database slow / appserver")
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 all engineering tools required available and in service? 	yes	
Tooling 	Was there a runbook for all known issues present? 	no 	Setting to no as we need to update the DDoS playbook. We have also updated the question from now on to reflect that.
Total score (count of all “yes” answers above)	Total score (count of all “yes” answers above) 	7