Cases2 cases

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1. IL-0400 Public sector sites across Wales lost connectivity for over 8 hours as a PE router wrongly advertised a default route

   PSBA2026

   Symptoms

   On 25 March 2026 from about 16:40, public sector organisations on the PSBA network across Wales lost connectivity at their sites. The Service Desk saw about 400 alerts at 16:58, when a Major Incident was declared, about 1,500 at 17:05 and about 5,000 across Wales at 17:08, while councils, a fire and rescue service and Natural Resources Wales phoned in to report sites down.

   Network unreachableIntermittent connection failuresLink flapping

   Trigger

   At 16:30 a route map change was applied, outside formal change control, on a PSBA core Provider Edge (PE) router to leak MPLS VPN routes, so that legacy Capita-operated UPS devices in a /16 subnet could be managed by BT/PSBA. The change was removed at 16:40.

   Root cause

   Configuration change

   Component

   BGP routing

   Contributing factor

   Ineffective rollbackMissed in reviewLimited debug accessOverlapping failures

   Detection

   At 16:57 Mid Wales Fire & Rescue Service phoned in a loss of connectivity at its Presteigne site, and at 16:58 a case was opened in Service Now for a group of about 400 alerts and a Major Incident was declared.

   Remediation

   • Removed the route map change from the PE router at 16:40
   • Changed QoS on the BGP to bring back the management links, after which alarms cleared
   • Cleared routes and reset inbound BGP advertisements, which did not stop the default route being advertised
   • Corrected the configuration issue affecting the internet learned route at 01:02
   • Performed a controlled reload of the affected router at 01:10, which restored customer services and management connectivity

   Action items

   • Reinforce change control requirements with an internal briefing on formal change submission, the risks of unplanned changes and roles during planned and emergency changes
   • Create a dedicated Microsoft Teams channel as the single real-time communication point for all live P1 and Major Incidents
   • Explore disaster recovery and business continuity test exercises for major or P1 incidents
   • During loss of management access, have all technical teams assess customer impact from what reporting organisations provide, captured and shared in real time by the Service Desk and Incident Management
   • Investigate a fixed link between Capital Quarter and the PSBA management racks in Vantage Data Centre at Newport, with dedicated management terminals and two-factor authentication for access outside the secure management platform
   • Improve initial triage with stronger probing questions when incidents are reported and keep reassessing and communicating impact throughout the incident
   • Review the P1 and Major Incident process so escalation criteria and timeframes are clearly defined, and train the Service Desk to recognise and escalate them early
   • Review the PSBA estate for legacy configuration, set processes and timeframes for removing it and add controls so it is not introduced again
   • Review email and SMS distribution lists and processes and reinforce Service Desk training on customer communications during P1 and Major Incidents

   Lessons

   The report names eight lessons: a change was made outside PSBA change control; internal communication during the Major Incident was slow and fragmented; the organisation was not ready for a network-wide incident; losing management access stopped the resolver groups from seeing the network state and customer impact; the resolver groups did not understand customer impact in enough detail, which delayed finding the root cause; escalation to PSBA management was slow; legacy configuration left in the network contributed; and email and SMS communications did not reach some customers in time.

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2. IL-0230 kube-proxy sync failures during a Kubernetes upgrade corrupted node iptables, and CircleCI jobs stopped starting

   CircleCI2023

   Symptoms

   On 14 March 2023 at about 18:00 UTC, communication errors rose on one CircleCI service, and pipelines for all customers began to start late until jobs did not run at all. Within an hour the errors had spread to many services and to every function of the application, including the CircleCI UI and API.

   Service outageIntermittent connection failuresDNS resolution failures

   Trigger

   At about 17:40 UTC on 14 March the infrastructure team resumed the upgrade of the main production Kubernetes cluster with a changed approach for some components, after a first attempt on 13 March had been rolled back. The ongoing upgrade left kubelet and kube-proxy at mismatched versions.

   Root cause

   Breaking change in an upgrade

   Component

   kube-proxykubeletCoreDNSClient-side DNS resolver and cache

   Contributing factor

   Partial rolloutIneffective rollbackMonitoring blind spotHarmful manual action

   Detection

   At 18:00 UTC engineers saw communication errors rise on one service, then job processing delays climbing and job queues backing up across several services. The kube-proxy "Sync failed" errors were found only in the analysis after the incident.

   Remediation

   • Restarted every node in the cluster so each node built a fresh iptables ruleset
   • Restarted a separate pool of dependencies so jobs using contexts or the machine executor ran again
   • Added capacity to work through the backlog of jobs
   • Restarted the RabbitMQ nodes to fix a few corrupted queues

   Action items

   • Improve the Kubernetes upgrade process to limit the risk of future upgrades
   • Add metrics and alerts for kube-proxy sync errors
   • Evaluate ways to make the RabbitMQ infrastructure more resilient

   Lessons

   No single trigger caused the incident. Because networking underlies everything in the cluster, Kubernetes upgrades carry inherent risk, and CircleCI's risk mitigation did not hold up when several events interacted.

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