Cases2 cases

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1. IL-0092 Upgrading ingress-nginx from 1.12.0 to 1.14.3 brought a newer ModSecurity and OWASP Core Rule Set whose false positives blocked HMPPS Auth, so users could not sign in to their applications

   UK Ministry of Justice2026

   Symptoms

   At 08:56 on 30 March 2026, about an hour and three quarters after the rollout of a new ingress-nginx to production began, the MoJ Cloud Platform team noticed messages in the #hmpps-auth-audit-registers Slack channel about ModSecurity unexpectedly blocking requests. Users in HMPPS also raised incidents with the MoJ service desk.

   High error rateService outage

   Trigger

   The Cloud Platform team began deploying ingress-nginx 1.14.3, on images maintained by Chainguard, to the three production ingresses at 07:11 on 30 March 2026.

   Root cause

   Breaking change in an upgrade

   Component

   Ingress controllerWeb application firewall rules

   Contributing factor

   Unrepresentative staging

   Detection

   At 08:56 the Cloud Platform team saw messages in the #hmpps-auth-audit-registers Slack channel showing ModSecurity blocking requests unexpectedly; HMPPS users also raised incidents with the MoJ service desk.

   Remediation

   • rolled the ingress-nginx deployment back to the previous version, from 09:14 to 09:43
   • HMPPS applied ModSecurity rule exclusions for the rules blocking traffic to HMPPS Auth
   • added a temporary global exclusion for the CRS rule triggered by the PostHog cookie
   • redeployed ingress-nginx 1.14.3 with both exclusions in place, completed at 14:00

   Action items

   • Rescope the PostHog cookie so it is no longer sent with requests to all *.justice.gov.uk services
   • Remove the temporary global exclusion once the PostHog cookie has expired from enough users' browsers
   • Remind service teams to run dev and test workloads through the non-production ingress controllers so future ModSecurity and CRS updates are tested
   • Run production and non-production workloads in separate clusters in Cloud Platform 3.0, so non-production workloads must use the non-production ingress

   Lessons

   An ingress controller upgrade that bundles a web application firewall also changes which requests are allowed, not only how they are routed. A beta or non-production ingress only catches false positives for traffic that actually passes through it, and teams that keep their test workloads on the production ingress miss them. A fix on the client side, such as rescoping a cookie, takes effect only when old cookies have expired in users' browsers, so the rule change has to wait for it or ship with an exclusion.

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2. IL-0117 A scheduled maintenance and an ingress upgrade on OpenAI's user-facing clusters caused a networking control plane regression that briefly broke the data plane, and the services that restarted then overwhelmed a backend persistence store with a heavy first-start query

   OpenAI2024

   Symptoms

   On August 16, 2024 from 11:38 AM to 1:16 PM PT, the OpenAI primary API was unreliable: ChatGPT conversations succeeded less often, and logging in and creating accounts were affected. The status page called it elevated error rates for ChatGPT and the Platform API. The incident came in two waves, of 44 and 15 minutes.

   High error rateDatabase overload

   Trigger

   A scheduled maintenance combined with an upgrade to the ingress of OpenAI's user-facing clusters.

   Root cause

   Breaking change in an upgrade

   Component

   Ingress controllerApplication database

   Contributing factor

   No staged rolloutAutomation amplification

   Action items

   • Mitigate the networking control plane regression and validate that control plane restarts do not interfere with the clusters' data plane
   • Change service software to start faster and remove the first-start query, relieving the persistence layer
   • Deploy configuration changes that optimise the networking control plane's effect on the clusters' ability to handle traffic
   • Remove the expensive database query from critical startup paths
   • Add monitoring and alerting for networking control plane issues
   • Introduce staged rollouts with longer soak time for infrastructure changes
   • Audit systems for other slow queries that may affect service start time

   Lessons

   A brief connectivity loss turned into a long outage because recovery itself was expensive: the services that restarted overwhelmed one backend persistence store with a heavy first-start query. Keeping costly queries off startup paths shortens recovery, and staged rollouts with longer soak time limit how many systems an infrastructure regression reaches before it is caught.

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