How to add Kubernetes livenessprob and readinessprob to my .net core console application?

Question

I have a simple consol application I want there is rabbitmq connection as a consumer and there is a database connection to SQL Server.

Before Containarize the application. There is some commands I have implemented, For example if I enterned X the application will exit so internaly I stop the consumer first and make sure there is no pending message and then gracefully I exit the application.

After Containarize the application I did successfully containarize the application and working perfectly under kuberenetes cluster but my problem is that How to send command to my application ?

For example I want to implement Livenessprob: check the database connection

Before terminating the pod I want to write x to my running console to implement gracefully exit the application without messages loss.

      postStart:
        exec:
          command: []
      preStop:
        exec:
          command: []

I expecting the solution to be a specific command which is writing to my running console application But how to send that command? Or how to make my console able to receive commands from kubernetes?

Answer 1

In Kubernetes, you can set up Liveness, Readiness, and Startup Probes. Check the official Kubernetes Documentation page on this topic.

The Kubelet Node agent can perform these probes on running Pods using 3 different methods:

• HTTP: The Kubelet probe performs an HTTP GET request against an endpoint (like /health), and succeeds if the response status is between 200 and 399
• TCP: The Kubelet probe attempts to connect to your container on a specified port. If it can establish a TCP connection, then the probe succeeds.
• Container Command: The Kubelet probe executes a command inside of the running container. If the exit code is 0, then the probe succeeds.

If you wish you can define a liveness probe command:

• you can run some command:

livenessProbe:
  exec:
    command:
    - cat
    - /tmp/healthy
  initialDelaySeconds: 10
  periodSeconds: 5

To perform a probe, the kubelet executes the command cat /tmp/healthy in the target container. If the command succeeds, it returns 0, and the kubelet considers the container to be alive and healthy. If the command returns a non-zero value, the kubelet kills the container and restarts it.

• you can run some bash script located in the container:

livenessProbe:
  exec:
    command: 
    - sh 
    - -c 
    - /health/ping_liveness_local.sh
...

• or write the bash script in the probe section:

  livenessProbe:
    exec:
      command:
      - /bin/sh
      - -c
      - |-
        echo 'if the app writes a PID file, we could check that it is still alive';
        [ -f /run/my-application-web.pid ] && ps -A | grep my-application-web
 ...

Container Lifecycle Hooks (docs)

There are two types of hook handlers that can be implemented for Containers:

• HTTP - Executes an HTTP request against a specific endpoint on the Container.
• Exec - Executes a specific command, such as pre-stop.sh, inside the cgroups and namespaces of the Container.

Example:

spec:
  containers:
    lifecycle:
      postStart:
        exec:
          command: ["/bin/sh", "-c", "echo Hello from the postStart handler > /usr/share/message"]
      preStop:
        exec:
          command: ["/bin/sh","-c","nginx -s quit; while killall -0 nginx; do sleep 1; done"]

And as you mentioned in comments you can use the touch /someDir/someFile preStop command to create a file and watch it in your app to shutdown gracefully.