Incidents/2024-05-31 Image hotlinking

== Summary ==
Hotlinking of an image on Commons caused link saturation in the eqsin datacentre. 
==Timeline==
Link to a specific offset in SAL using the SAL tool at https://sal.toolforge.org/ (example)
All times in UTC.
*10:47 Page for port utilisation arrives OUTAGE BEGINS
*11:14: VictorOps page: DDos Detected (eqsin)
*12:01 hnowlan adds requestctl/request-actions/cache-upload/hotlink_from_jio_blomen.yaml and requestctl/request-patterns/req/cache_buster_nnn.yaml. No effect
*12:08 Incident opened. Kamila becomes IC
*12:33 hnowlan manually deploys varnish frontend rule 
*12:48 All damaging requests for URL in question are receiving HTTP 429 in response 
*12:39 <+jinxer-wm> RESOLVED: DDoSDetected: FastNetMon has detected an attack on eqsin #page - https://bit.ly/wmf-fastnetmon - https://w.wiki/8oU - https://alerts.wikimedia.org/?q=alertname%3DDDoSDetected OUTAGE ENDS
==Detection==
This incident was detected via paging for port utilisation in eqsin: 
<+jinxer-wm> FIRING: Primary outbound port utilisation over 80%  #page: Alert for device asw1-eqsin.mgmt.eqsin.wmnet - Primary outbound port utilisation over 80%  #page
Additionally FastNetMon detected what it perceived as a DDoS. This was more or less correct as the behaviours witnessed are similar to a simple DDoS attack.
==Conclusions ==
This was a somewhat familiar pattern, as we have seen similar issues in the past on a larger scale. 
===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==
* …
Add links to information that someone responding to this alert should have (runbook, plus supporting docs). If that documentation does not exist, add an action item to create it.
==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? 	yes	
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)? 	yes	
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? 	no 	
Process 	Is there a phabricator task for the incident? 	no 	
Process 	Are the documented action items assigned? 	no 	
Process 	Is this incident sufficiently different from earlier incidents so as not to be a repeat occurrence? 	no 	
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) 	9