Deploy Stateless Workload on Kubernetes

With Pods, Deployments, Daemonsets, and Services

We answered questions like:

• What is a minimum deployable unit (aka Pod) in Kubernetes?
• What are Deployment and DaemonSet? How are these related to a Pod?
• How to set resource quota limits (CPU and Memory) for the Pods and Namespaces?
• What is a Service? What are different types of Service?
• What are a few important things to keep in mind while working with the stateless workload on Kubernetes?

This was the 4th Collective Talk of the Cloud Native Series scheduled from September 2018 to November 2018.

Recap‌

Command Reference

Prerequisites:

1. awscli and kubectl are installed on the local machine.

2. a Kubernetes cluster (let’s say k8s.ennate.academy) with aws-iam-authenticator daemonset is already installed on the AWS cluster using kops. (How to Install k8s cluster with IAM support using kops?)

3. a k8s namespace is already created‌

$ cat <<EOF | kubectl apply -f -
apiVersion: v1
kind: Namespace
metadata:
  name: dev
EOF

Pods:

1. deploy a pod with two containers:‌

$ cat <<EOF | kubectl apply -f -
apiVersion: v1
kind: Pod
metadata:
  name: app
spec:
  containers:
  - name: whale
    image: salitrapraveen/whale:latest
    ports:
    - containerPort: 80
      name: http
      protocol: TCP

  - name: alpine
    image: alpine:3.8
    command: ['sh', '-c', 'echo Hello Kubernetes! && sleep 3600']
EOF

2. deploy a pod with resource quota:‌

$ cat <<EOF | kubectl apply -f -
apiVersion: v1
kind: Pod
metadata:
  name: alpine
spec:
  containers:
  - name: alpine
    image: alpine:3.8
    command: ['sh', '-c', 'echo Hello Kubernetes! && sleep 3600']
    resources:
      requests:
        memory: "64Mi"  // Ki, Mi, Gi, Ti, Pi, Ei
        cpu: "250m" // 1CPU = 1 AWS vCPU, 1GCP Core, 1 Azure vCore
      limits:
        memory: "128Mi"
        cpu: "500m" 
EOF

3. pod specific kubectl commands:‌

$ kubectl describe pod POD_NAME
$ kubectl logs POD_NAME [-c CONTAINER_NAME]
$ kubectl exec -it POD_NAME [-c CONTAINER_NAME] /bin/sh
$ kubectl delete pod POD_NAME

Deployments:

1. create a deployment with 5 replicas of a pod:‌

apiVersion: apps/v1
kind: Deployment
metadata:
  name: whale-deployment
spec:
  replicas: 5
  strategy:
    type: RollingUpdate
  selector:
    matchLabels:
      app: whale-app
  template:
    metadata:
      labels:
        app: whale-app
    spec:
      containers:
      - name: whale
        image: salitrapraveen/whale:latest
        ports:
        - containerPort: 80
          name: http

      - name: alpine
        image: alpine:3.8
        command: ['sh', '-c', 'echo Hello Kubernetes! && sleep 3600']
        env:
        - name: SOME_ENV_VAR
          value: awesome
EOF

2. deployment specific kubectl commands:‌

$ kubectl get deployments
$ kubectl get replicasets
$ kubectl scale deployment DEPLOYMENT_NAME --replicas=COUNT
$ kubectl describe deployment DEPLOYMENT_NAME
$ kubectl edit deployment DEPLOYMENT_NAME
$ kubectl delete deployment DEPLOYMENT_NAME

DaemonSets:

1. create a daemonset that deploys pods on the master nodes (see nodeSelector and tolerations in the spec):‌

$ cat <<EOF | kubectl apply -f -
apiVersion: apps/v1
kind: DaemonSet
metadata:
  name: whale-daemon
spec:
  selector:
    matchLabels:
      app: whale-app
  template:
    metadata:
      labels:
        app: whale-app
    spec:
      nodeSelector:
        node-role.kubernetes.io/master: ""
      tolerations:
      - effect: NoSchedule
        key: node-role.kubernetes.io/master

      containers:
      - name: whale
        image: salitrapraveen/whale:latest
        ports:
        - containerPort: 80
          name: http

      - name: alpine
        image: alpine:3.8
        command: ['sh', '-c', 'echo Hello Kubernetes! && sleep 3600']
        env:
        - name: SOME_ENV_VAR
          value: awesome
EOF

2. daemonset specific kubectl commands:‌

$ kubectl get daemonsets 
$ kubectl describe daemonset DAEMONSET_NAME
$ kubectl edit daemonset DAEMONSET_NAME
$ kubectl delete daemonset DAEMONSET_NAME

Services:

1. create a ClusterIP (default) type service:‌

$ cat <<EOF | kubectl apply -f -
apiVersion: v1
kind: Service
metadata:
  name: whale-service
spec:
  selector:
    app: whale-app
  ports:
  - protocol: TCP //supports TCP, UDP and SCTP
    port: 8080 //port where service would be listening for the TCP requests
    targetPort: 80 //containerPort of the pod. Value can be a string name of the containerPort as well.
EOF

2. create a NodePort type service:‌

$ cat <<EOF | kubectl apply -f -
apiVersion: v1
kind: Service
metadata:
  name: whale-service
spec:
  selector:
    app: whale-app
  type: NodePort
  ports:
  - protocol: TCP
    port: 8080
    targetPort: 80
    nodePort: 30270 //k8s assigns a random port (30000-32767) if not specified
EOF

3. create a LoadBalancer type service:‌

$ cat <<EOF | kubectl apply -f -
apiVersion: v1
kind: Service
metadata:
  name: whale-service
spec:
  selector:
    app: whale-app
  type: LoadBalancer
  ports:
  - protocol: TCP
    port: 8080
    targetPort: 80
EOF

4. create a ExternalName type service:‌

$ cat <<EOF | kubectl apply -f -
apiVersion: v1
kind: Service
metadata:
  name: whale-service
spec:
  type: ExternalName
  externalName: my.database.example.com
EOF

5. service specific kubectl commands:‌

$ kubectl get services 
$ kubectl get endpoints
$ kubectl edit service SERVICE_NAME
$ kubectl delete service SERVICE_NAME