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

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.

Answer 3

Using wait-for-it.sh is actually quite easy:

  initContainers:
  - name: wait-for-app1
    image: image-docker-containing-sh
    args:
    - /bin/sh
    - -c
    - /usr/app/wait-for-it.sh app1:<portapp1> -t 0

Of course retries and timeouts are the way to go, but this works great as a workaround.

Answer 4

initContainers:
    - name: wait-for-dependent-service
      image: stefanevinance/wait-for-200
      env:
        - name: URL
          value: http://dependent-service.{{.Release.Namespace}}.svc.cluster.local:3000

Using https://hub.docker.com/r/stefanevinance/wait-for-200/