Cases2 cases

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1. IL-0034 A crashing stats agent sidecar marked every pod unready and the service mesh pulled all services out of traffic

   Airbnb2019

   Symptoms

   An operation to upgrade the stats agent in Kubernetes was announced in advance, with a warning that metrics might be unavailable to services for a few minutes. A few minutes later a reply came in saying that all of the sender's Kubernetes services seemed to be down.

   Probe failuresService outage

   Trigger

   A scheduled upgrade of the stats agent sidecar, during which the agent container crashed.

   Root cause

   Faulty deployment

   Component

   Telemetry agentService discovery

   Contributing factor

   Unverified assumptionExcessive blast radius

   Detection

   A reply to the operation announcement, a few minutes later, said that all of the sender's Kubernetes services appeared to be down.

   Action items

   • Mark logging, tracing and stats agent containers as non-critical and leave them out of the service mesh's pod readiness check

   Lessons

   Every container in a pod affects the pod's readiness, so each sidecar needs a deliberate decision about how its health should count. A sidecar that crashes is not ready even when it has no probes, and any logic that requires all containers to be ready will take the pod out of traffic.

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2. IL-0051 A third-party log shipping client leaked file descriptors with every new container until nodes failed with too many open files

   thredUP2018

   Symptoms

   While thredUP's move to Kubernetes seemed to be going well, Datadog showed the number of open files on the nodes climbing steadily, with no obvious reason.

   Service outageFile descriptor exhaustion

   Trigger

   Containers starting on a node, which in Kubernetes happens constantly with every deploy and every pod that moves between nodes.

   Root cause

   Software defect

   Component

   Telemetry agent

   Contributing factor

   Unverified assumption

   Detection

   Datadog showed the number of open files on the nodes rising.

   Remediation

   • killed the affected node, brought up a new one and redeployed

   Action items

   • Move away from the log aggregation vendor

   Lessons

   Libraries and agents that worked with the EC2 deployment lifecycle may not cope with Kubernetes, where containers start, stop and move between nodes constantly. Each one needs to be checked against the new lifecycle instead of being trusted because it worked before.

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