Difficulty: beginner
Estimated Time: 30 minutes

Before diving into the Operator Framework, this section will give an overview of Kubernetes API fundamentals. Although the Operator SDK makes creating an Operator fun and easy, understanding the structure and features of the Kubernetes API is required.

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Kubernetes API Fundamentals

Step 1 of 5

Kubernetes Manifests

Let's begin my creating a new project called myproject:

oc new-project myproject


Create a new pod manifest that specifies two containers:

cat > pod-multi-container.yaml <<EOF
apiVersion: v1
kind: Pod
metadata:
  name: my-two-container-pod
  namespace: myproject
  labels:
    environment: dev
spec:
  containers:
    - name: server
      image: nginx:1.13-alpine
      ports:
        - containerPort: 80
          protocol: TCP
    - name: side-car
      image: alpine:latest
      command: ["/usr/bin/tail", "-f", "/dev/null"]
  restartPolicy: Never
EOF


Create the pod by specifying the manifest:

oc create -f pod-multi-container.yaml


View the detail for the pod and look at the events:

oc describe pod my-two-container-pod


Let's first execute a shell session inside the server container by using the -c flag:

oc exec -it my-two-container-pod -c server -- /bin/sh


Run some commands inside the server container:

ip address
netstat -ntlp
hostname
ps
exit


Let's now execute a shell session inside the side-car container:

oc exec -it my-two-container-pod -c side-car -- /bin/sh


Run the same commands in side-car container. Each container within a pod runs it's own cgroup, but shares IPC, Network, and UTC (hostname) namespaces:

ip address
netstat -ntlp
hostname
exit