Interview › Istio & Service Mesh
What is outlier detection, and how does it eject unhealthy hosts?
Istio & Service Mesh · Basic level
Answer
Outlier detection is Envoy's mechanism for identifying unhealthy upstream endpoints and temporarily ejecting them from the load-balancing pool. In Istio, it is configured in a DestinationRule under trafficPolicy.outlierDetection.
Technical explanation
It can react to consecutive 5xx responses, gateway errors, local-origin failures, or success-rate based signals depending on configuration and protocol.
Ejected hosts are not removed forever; they are reintroduced after the ejection time, then evaluated again.
It complements Kubernetes readiness probes but catches runtime failures visible from client traffic.
Hands-on example
Troubleshoot ejection:
$ istioctl proxy-config clusters deploy/frontend -n app -o json | grep -i outlier
$ kubectl logs deploy/frontend -c istio-proxy -n app | grep -i outlier
Then correlate with destination pod logs and readiness status.
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