Kubernetes Readiness and Liveness with Spring Boot Actuator

In Kubernetes, "readiness" is the indicator that the service is ready to accept traffic, and is only performed at the beginning of a pod's life cycle. "Liveness" is a periodic health check that should indicate that the service is still functional within the pod.
More details can be found in the documentation at
https://kubernetes.io/docs/tasks/configure-pod-container/configure-liveness-readiness-probes/

Spring Boot is a stand-alone Spring environment well suited for micro services.
https://projects.spring.io/spring-boot/

Spring Boot has a bundle available called "Actuator" that exposes several helpful endpoints, one of which is a "health" endpoint. The simple version of this endpoint returns a simple JSON with a status UP or DOWN.
https://github.com/spring-projects/spring-boot/tree/master/spring-boot-actuator

One particular feature of the health endpoint that is useful is that besides the text indicator in the JSON response, it also signals up and down through the status code. UP = 200, and DOWN = 503 (Service Unavailable).

Putting this all together, the readiness and liveness configuration in the Kubernetes deployment YAML can look something like this:

readinessProbe:
httpGet:
  scheme: HTTP
  path: /health
  port: 8080
initialDelaySeconds: 240
periodSeconds: 5
timeoutSeconds: 5
successThreshold: 1
failureThreshold: 10
livenessProbe:
httpGet:
  scheme: HTTP
  path: /health
  port: 8080
initialDelaySeconds: 300
periodSeconds: 60
timeoutSeconds: 10
successThreshold: 1
failureThreshold: 3

In this example, we instruct Kubernetes to wait 240 seconds to allow the application to start before performing the check. It will retry up to 10 times with a five second pause between each try. It will wait for a maximum of 5 seconds for a result to be returned. After 10 failures, the pod will be restarted.

For the liveness check, we instruct Kubernetes to wait 300 seconds, and to check every 60 seconds. If three failures occur in a row, the pod will be restarted.