Kubernetes - wait for other pod to be ready

Question

I have two applications - app1 and app2, where app1 is a config server that holds configs for app2. I have defined /readiness endpoint in app1 and need to wait till it returns OK status to start up pods of app2.

It's crucial that deployment of app2 wait till kubernetes receives Http Status OK from /readiness endpoint in app1 as it's a configuration server and holds crucial configs for app2.

Is it possible to do this kind of deployment dependency?

Answer 1

You need to use initContainers. Following is an example of how you can do in your YAML file

initContainers: - name: wait-for-other-pod   image: docker.some.image   args:   - /bin/sh   - -c   - >     set -x;     while [ $(curl -sw '%{http_code}' "http://www.<your_pod_health_check_end_point>.com" -o /dev/null) -ne 200 ]; do       sleep 15;     done 

I have used curl to hit the health check endpoint, you can use any other UNIX command to check if the other pod is ready.

Answer 2

Yes, it's possible using Init Containers (also, see this blog post for some background re timing) but a better, more Kubernetes-native pattern is to use retries and timeouts rather than hard-coding dependencies in this way.