Cases2 cases

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1. IL-0187 A brief Spring Cloud Config Server downtime failed every client application's liveness probe, because the actuator health check included the config server, and Kubernetes restarted the pods in a kill loop

   Yonghyun Kim2025

   Symptoms

   While the Spring Cloud Config Server was briefly down for an upgrade, every client application began to answer its liveness probe with a failure saying it could not reach the config server.

   Probe failuresContainer crash loopService outage

   Trigger

   A downtime upgrade of the Spring Cloud Config Server made it stop responding for a short time.

   Root cause

   Dependency failure

   Component

   Liveness and readiness probes

   Contributing factor

   Unreviewed defaultsAutomation amplificationExcessive blast radius

   Lessons

   A liveness probe that includes an external dependency turns a short outage of that dependency into a restart loop of every client. Keep external dependencies out of liveness checks and handle temporary problems with readiness probes. Libraries can add health indicators to Spring Boot's actuator health endpoint automatically, so check what the probe path actually reports. The author ran another Kubernetes environment for two years without liveness probes, relying on strict readiness probes and on the application terminating itself on unrecoverable faults.

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2. IL-0103 During an EKS node AMI update, Istio sidecars crash-looped because hundreds of pods restarting at once overloaded the external certificate authority behind istiod

   Tetrate (unnamed U.S. federal customer)2025sev1

   Symptoms

   While the customer was updating the AMIs of its Amazon EKS nodes across more than 30 clusters running Istio, sidecar-injected workloads in one cluster failed to start and showed CrashLoopBackOff.

   Container crash loopProbe failures

   Trigger

   Updating the EKS node AMIs, which started hundreds of sidecar-injected pods at the same time.

   Root cause

   Dependency failure

   Component

   IstioAdmission webhookNode operating system image

   Contributing factor

   Unreviewed defaultsUnknown limit

   Detection

   Sidecar-injected workloads in the updated cluster failed to start and showed CrashLoopBackOff; the customer raised a Severity 1 ticket and a Tetrate engineer was reviewing logs within six minutes.

   Remediation

   • scaled istiod down temporarily from 40 replicas to 1 to slow Istio's internal processes and ease the load on the CA
   • deleted the CertificateSigningRequests stuck in the Approved, Failed state
   • restarted the pods gradually in a controlled order instead of all at once

   Lessons

   When a mesh hands certificate signing to an external CA, every pod start becomes a signing request to that CA, so a mass restart such as a node image rollout can overload it. Sidecars then abort under istiod's 10-second default CA timeout even though the CSRs are eventually signed. Restarting pods in controlled batches keeps the request rate within what the CA can handle. The author's point is that diagnosing such a failure means looking at the whole service mesh ecosystem, including its external dependencies, not only Istio.

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