k8s Pods

PODs
- smallest object in k8s, contains containers, can contain one or more containers
- scale service by creating more pod instances.
- additional container could be helper container.
- network space is shared between containers in the same pod, they can communicate on localhost.
Static Pods
- On standalone VM, the kubelet can be configured to
  - read pod definitions from
    1. (Option:--pod-manifest-path=/etc/kubernetes/manifests).
      - ps ax | grep kubeconfig
    2. kubeconfig.yaml staticPodPath: /etc/kubernetes/manifest.
  - It also assures they stay alive.
  - Only POD's , nothing else.
  - view with docker ps
  - the kubeadm k8s setup uses static pods to run the k8s management software as pods on nodes.
- Static Pods and DaemonSets are ignored by the Kube-Scheduler

Pod, eq in Docker ENTRYPOINT->command & CMD->args

apiVersion: v1
kind: Pod
metadata:
  name: ubuntu-sleeper-pod
spec:
  containers:
    - name: ubuntu-sleeper
      image: ubuntu-sleeper
      command: ["sleep2.0"]
      args: ["10",]
      ...
      envFrom:
        - configMapRef:
             name: app-conf-map
        - secretRef:
             name: app-secret
      ...
      env:
        - name: APP_COLOR1
          value: pink

        - name: App_COLOR2
          valueFrom:
               configMapKeyRef:

        - name: App_PWD
          valueFrom:
               secretKeyRef:
                  name: app-secret
                  key: DB_Password    

      ...
  volumes:
    - name: app-secret-volume
      secret:
         secretName: app-secret

Multi-container pods
- Types
  1. SideCar
  2. Adapter
  3. Ambassador
- All containers are expected to stay alive in POD. If any fail, the POD restarts.
  - InitContainers: separate section in line with containers:
    - Runs one at a time, before Containers: and must all complete before real container starts.
      - if an InitContainer fails, Pod restarts