application-lifecycle.adoc

Application lifecycle

create a deployment

kubectl create -f <deployment-defn>
kubectl rollout status <deployment-name>
kubectl rollout history <deployment-name>

to update

kubectl apply -f
kubectl set-image <deployment-name> <container>=<image>

rollback

kubectl rollout undo <deployment>

Dockerfile and pod-definition

# 1. dockerfile with no default command

Entrypoint takes arguments that are supplied on command line during docker/kubectl run or from kubernetes manifests Dockerfile: ENTRYPOINT ["python", "app.py"]

# 2. Dockerfile with default command that can be overridden from pod defn

ENTRYPOINT ["python", "app.py"]
CMD ["--color", "red"]

# 3. pod-definition

  - name: simple-webapp
    image: kodekloud/webapp-color
    args: ["--color", "green"] --> overrides the command and passed as a command

Configmaps

k get configmap
k create configmap <name> --from-literal=KEY=VALUE

apiVersion: v1
kind: Pod
metadata:
  name: dapi-test-pod
spec:
  containers:
    - name: test-container
      image: k8s.gcr.io/busybox
      command: [ "/bin/sh", "-c", "env" ]
      env:
        # Define the environment variable
        - name: SPECIAL_LEVEL_KEY
          valueFrom:
            configMapKeyRef:
              # The ConfigMap containing the value you want to assign to SPECIAL_LEVEL_KEY
              name: special-config
              # Specify the key associated with the value
              key: special.how

Secrets use similar commands

creating multiple secrets

kubectl create secret generic db-secret --from-literal=DB_Host=sql01 --from-literal=DB_User=root --from-literal=DB_Password=password123

Volume mounts and host paths

  containers:
  - name: app
    image: kodekloud/event-simulator
    volumeMounts:
    - mountPath: /log
      name: log-volume

  - name: sidecar
    image: kodekloud/filebeat-configured
    volumeMounts:
    - mountPath: /var/log/event-simulator/
      name: log-volume

  volumes:
  - name: log-volume
    hostPath:
      # directory location on host
      path: /var/log/webapp
      # this field is optional
      type: DirectoryOrCreate

Secrets have type type: kubernetes.io/service-account-token