Kubernetes Tutorial · Kubernetes Basics · Lesson 4 of 26

Pods

The smallest deployable unit: one or more containers sharing a network namespace and volumes.

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What a pod is

A pod runs one or more containers that share an IP address, ports (localhost) and volumes. Most pods have one main container; helpers (sidecars, init containers) share its pod.

apiVersion: v1
kind: Pod
metadata:
  name: hello
  labels: {app: hello}
spec:
  containers:
    - name: main
      image: busybox:1.37
      command: ["sh", "-c", "echo hello from $(hostname); sleep 3600"]

Pods are disposable: when a node dies, its pods are gone. You rarely create pods directly; controllers (Deployments, Jobs, StatefulSets) create and replace them for you.

A pod with an init container and a shared volume

kubectl create namespace demo-pods > /dev/null
trap 'kubectl delete namespace demo-pods --wait=false > /dev/null' EXIT
cat > pod.yaml <<'EOF'
apiVersion: v1
kind: Pod
metadata:
  name: hello
  labels:
    app: hello
spec:
  initContainers:
    - name: prepare
      image: busybox:1.37
      command: ["sh", "-c", "echo 'prepared by the init container' > /work/msg"]
      volumeMounts: [{name: work, mountPath: /work}]
  containers:
    - name: main
      image: busybox:1.37
      command: ["sh", "-c", "cat /work/msg; echo 'main container running'; sleep 3600"]
      volumeMounts: [{name: work, mountPath: /work}]
  volumes:
    - name: work
      emptyDir: {}
EOF
kubectl -n demo-pods apply -f pod.yaml
kubectl -n demo-pods wait --for=condition=Ready pod/hello --timeout=120s > /dev/null
kubectl -n demo-pods logs hello
kubectl -n demo-pods get pod hello -o jsonpath='{.status.phase} on node {.spec.nodeName}{"\n"}'

Output

pod/hello created
prepared by the init container
main container running
Running on node rc-docs-control-plane

Run this on your computer — see “Get Started” for setup.

See Pods.

Test yourself

Why do you rarely create bare pods in production?

Pods are deprecated
Nothing recreates them when they die; controllers like Deployments do
Pods can't have labels
Pods can't run images

Show answer

Answer: Nothing recreates them when they die; controllers like Deployments do

A Deployment's ReplicaSet replaces pods that disappear.

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