How to add pod dependency in kubernetes as like 'depends_on' in docker-compose.yml

Question

I need to start kubernetes pods in a sequence like pod2 should start only when pod1 is up and running.

we can do this in docker-compose.yml using depends_on

Madrepore

possible duplicate of #50325177, see point 2) in original question. – Sindee

Answer 1

No, there is no built-in dependency management equivalent to depends_on available. In general, we assume loosely coupled services and as a good practice there should be no hard dependency in terms of start-up order, but retries and timeouts should be used. If you have to hardcode dependencies, you can use init containers. In your case, a init container in pod2 could simply query if pod1 (or better: the service in front of it) is ready in a while loop. The main container in pod2 is guaranteed only to be launched if and when the init container exits successfully.

Casebook

Why those two things should be mutually exclusive? Having retries doesn't mean there should be no dependencies. Having dependencies specified will likely speed-up start-up time of an app. I often see pods spinning in retries loop like mad until they finally make it in a correct order ... so not being able to specify dependencies easily is definitely not critical, but a nice to have feature. – Yesterday

Answer 2

There isn't a direct equivalent to dependency with Kubernetes primitives, as a workaround you can implement a readiness probe that will render pod2 unusable until it sees pod1 up and running.

Pilsen

Answer 3

You can use this pod-dependency-init-container that I have build. This will check if any pod with given labels is running before starting your pod.

Discreet

Answer 4

I have been working on such controller , need few more tests done and it will be published next week, utilizes deployment readiness statuses crds service accounts, cluster roles rolebindings etc.

Schleswigholstein