Using Docker in Kubernetes

deployment.yaml

---
# This creates a deployment where each pod has two containers:
#   - Docker Server: the actual docker engine.
#   - Docker Client: simple Ubuntu instance with docker cli so we can
#     test the docker things. In practice this would be some CI agent
#     like Azure Devops agent or Jenkins or anything at all.
# 
# After this deployment is created, wait for a bit for docker CLI to be installed
# in the client container. Then shell into it and use docker commands like docker build etc
# to test that things actually work.
apiVersion: apps/v1
kind: Deployment
metadata:
  name: docker-demo
  labels:
    app: docker-demo
spec:
  replicas: 1
  selector:
    matchLabels:
      app: docker-demo
  template:
    metadata:
      labels:
        app: docker-demo
    spec:
      tolerations:
      # So we can run on spot instances in Azure AKS, add your own as required.
      - effect: NoSchedule
        key: kubernetes.azure.com/scalesetpriority
        operator: Equal
        value: spot
      containers:
      # Docker server
      - name: server
        image: docker:20.10.17-dind
        env:
          # Required to talk plain HTTP, until we figure out how to talk over HTTPS or SSH.
          - name: DOCKER_TLS_CERTDIR
            value: ""
        securityContext:
          privileged: true

      # Docker client. Installs docker cli. All docker commands talk to docker server.
      # 
      # Once this is running we can shell into this container and try out docker commands.
      - name: client
        image: ubuntu:20.04
        env:
          - name: DOCKER_HOST
            value: "tcp://localhost:2375"
        command: ["/bin/bash"]
        args: 
        - "-c" 
        - |
          set -e
          echo "Installing docker client"
          (
            set -x
            # Install docker client form MSFT repository
            apt-get update
            apt-get install --no-install-recommends -y ca-certificates
            apt-get install --no-install-recommends -y curl

            # Install repository configuration
            # Install Microsoft GPG public key
            curl -sSL https://packages.microsoft.com/config/ubuntu/20.04/prod.list | tee /etc/apt/sources.list.d/microsoft-prod.list
            curl -sSL https://packages.microsoft.com/keys/microsoft.asc | tee /etc/apt/trusted.gpg.d/microsoft.asc

            # Finally docker client
            apt-get update
            apt-get install -y moby-cli
          )

          # Finally a sleep loop
          while true
          do 
            echo -n 'sleeping: '; date; sleep 10; 
          done