Kubernetes API Fundamentals

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.

Let’s begin by creating a new project called myproject:

oc new-project myproject

If the project already exits, make sure we are currently scoped to it:

oc 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