Kubernetes init containers

2 min read | by Jordi Prats

Kubernetes init containers are a special container that runs before the main containers on the Pod. They are usually used used for setting up the environment and populate some shared storage to be used for the actual containers.

We can add them using spec.initContainers on the same way we use spec.containers:

apiVersion: v1 kind: Pod metadata:  name: my-pod spec:  initContainers:  - image: my-init-image  name: my-init  containers:  - image: my-app-image  name: my-app  - image: my-other-app-image  name: my-other-app

We must take into account that:

  • Init containers are not expected to keep running, they must finish it's task.
  • Each init container must complete successfully before the next one starts.

If we use --watch with kubectl get pods we can see how this works:

$ kubectl get pods --watch NAME READY STATUS RESTARTS AGE pet2cattle-8475d6697-jbmsm 0/1 Pending 0 0s pet2cattle-8475d6697-jbmsm 0/1 Pending 0 0s pet2cattle-8475d6697-jbmsm 0/1 Init:0/4 0 0s pet2cattle-8475d6697-2sk4m 0/1 Init:1/4 0 4s pet2cattle-8475d6697-2sk4m 0/1 Init:2/4 0 5s pet2cattle-8475d6697-2sk4m 0/1 Init:2/4 0 6s pet2cattle-8475d6697-2sk4m 0/1 Init:3/4 0 7s pet2cattle-8475d6697-2sk4m 0/1 PodInitializing 0 8s pet2cattle-8475d6697-2sk4m 0/1 Running 0 9s pet2cattle-8475d6697-2sk4m 0/1 Running 0 41s pet2cattle-8475d6697-2sk4m 1/1 Running 0 2m20s

Posted on 21/06/2021

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