Kubernetes - Pod

Last Updated: 2023-08-27

apiVersion: v1
kind: Pod

Use controllers to manage pods, do not manage pods directly

Deployment -> ReplicaSet -> Pod

Containers in a Pod

In the simplest cases, each pod just have 1 container; in some cases each pod has more than 1 pods; with sidecars, each pod has at least 2 containers.

Order: first start spec.initContainers then spec.containers; no specific order when sttarting containers in spec.containers.

Native Sidecar Containers since Kubernetes 1.28

Before 1.28:

• sidecar container is part of spec.containers
  • if app container starts faster than sidecar container, or shuts down after the sidecar container (i.e. sidecar container life-syscle shorter than app container), the app container cannot access the network.
  • if app container exists but sidecar containers runs, the pod will be running indefinitely.
  • init containers run before sidecar container, so cannot access the network.

After 1.28:

• sidecar container is part of spec.initContainers but with restartPolicy: Always
  • later containers in the list of spec.initContainers, and all normal spec.containers will not start until the sidecar container is ready.
  • the pod will terminate even if the sidecar container is still running.

Example:

apiVersion: v1
kind: Pod
spec:
  initContainers:
  - name: network-proxy
    image: network-proxy:1.0
    restartPolicy: Always
  containers:
  ...