While I’ve manually configured Kubernetes to create proof-of-concept sandbox systems, that is an inefficient approach for production systems. The kubectl create command can use a yaml file (or json, if you prefer that format). I maintain my manifests in a Git repository so changes can be tracked (and so I know where to find them!). Once you have a manifest, it’s a matter of using “kubectl create -f manifest1.yaml” or “kubectl create -f manifest1.yaml -f manifest2.yaml … -f manifestN.yaml” to bring the ‘stuff’ online.

But what goes into a manifest file? The following file would deploy four replicas of the sendmail container that is retained in my private registry.

If the namespaces have not been created,

apiVersion: v1
kind: Namespace
metadata:
  name: sendmailtest

The command “kubectl get ns” will list namespaces on the cluster. Note that ‘deployment’ items were not available in the v1 API, so the v1beta1 version needs to be specified to configure a deployment.

---
apiVersion: v1
kind: Pod
metadata:
  name: sendmail
  namespace: sendmailtest
  labels:
    app: sendmail
spec:
  containers:
    - name: sendmail
      image: sendmail
      ports:
        - containerPort: 25
---
apiVersion: v1beta1
kind: Deployment
metadata:
  name: sendmail
spec:
  replicas: 4
  template:
    metadata:
      labels:
        app: sendmail
    spec:
      containers:
        - name: sendmail
          image: 'rushworthdockerregistry/sendmail/sendmail/sendmail:latest'
          ports:
            - containerPort: 25

---
apiVersion: v1
kind: Service
metadata:
  name: sendmail-service
  labels:
    name: sendmail-service
spec:
  ports:
    - port: 25
      targetPort: 25
      protocol: TCP
      name: smtp
  selector:
    app: sendmail
  type: ClusterIP