Kubernetes graceful shutdown of a Spring Boot Tomcat application

Question

I am running a Java Spring Boot boot application on Tomcat in a Kubernetes cluster, I am using a lifecycle hook to shut down Tomcat before the container gets terminated. Also defining a termination grace period of 30 secs.

Expected behaviour: tomcat shuts down gracefully when I kill a pod or delete a deployment.

Actual behaviour: tomcat shuts down abruptly.

lifecycle:
          preStop:
            exec:
              command:
              - /usr/local/tomcat/bin/catalina.sh

Can anyone help please?

Answer 1

In Kubernetes, the preStop hook is executed before the pod is terminated.

For the above use case, tomcat process has to be shutdown gracefully before the pod is terminated when a pod / deployment is deleted.

The following sample pod definition works, by graceful shutdown of the tomcat server, before pod termination. Note: The container in this definition is FROM tomcat:9.0.19-jre8

apiVersion: v1 
kind: Pod 
metadata:
  name: demopod
spec:
  containers:
  - image: demo:web
    name: demo-container
    ports:
    - containerPort: 8080
    lifecycle:
      postStart:
        exec:
          command: ["/bin/sh", "-c", "echo Hello from the postStart handler > /usr/share/message"]
      preStop:
        exec:
          command: ["/bin/sh", "-c", "echo Stopping server > /usr/share/message1; sleep 10; sh /usr/local/tomcat/bin/catalina.sh stop"]

In the above definition file, we run three commands (change as per need).

1. Write a shutdown message into /usr/share/message1

2. sleep 10 (Just to give time to view pod / container logs)

3. Run Catalina.sh stop script to stop the tomcat server.

To Debug: For PreStop, if the handler fails, an event is broadcasted, the FailedPreStopHook event. You can see these events by running kubectl describe pod <pod_name>

Refer below post for more detailed instructions: http://muralitechblog.com/kubernetes-graceful-shutdown-of-pods/

Shutdown logs: