Kubernetes Container Probes

External

• https://kubernetes.io/docs/tasks/configure-pod-container/configure-liveness-readiness-probes
• https://kubernetes.io/docs/concepts/workloads/pods/pod-lifecycle/#container-probes

Internal

• Kubernetes Pod and Container Concepts

Container Liveness Check

The result of the container liveness check is used by Kubernetes to know when to restart the container (Not the pod? How about atomicity?)

Container Readiness Check

The result of the container readiness check is used by Kubernetes to know when the container is ready to accept traffic. The pod is considered ready wen all of its containers are ready. The readiness check is used by services to decide whether to send traffic into the pod or not. Container will be removed from service endpoints if the probe fails.

Probe Template

https://kubernetes.io/docs/reference/generated/kubernetes-api/v1.14/#probe-v1-core

kind: Pod
spec:
  containers:
  - name: ...
    readinessProbe|livenessProbe:
      exec:

Example:

readinessProbe:
  exec:
    command:
    - /bin/sh
    - -c
    - nodetool status | grep -E "^UN\s+${POD_IP}"
  failureThreshold: 3
  initialDelaySeconds: 90
  periodSeconds: 30
  successThreshold: 1
  timeoutSeconds: 5

Elements

initialDelaySeconds

Specifies the number of seconds after the container has started before liveness probes are initiated.