1.webapp-pod.yaml

# Create a simple web application pod hosted on port 8080
# Along with an additional container called sidecar to access resources directly from other container
# It also creates an init container which to demonstrate a initialization process before the container can get started
apiVersion: v1
kind: Pod
metadata:
  name: webapp
  namespace: demo
spec:
  # These containers are run during pod initialization
  initContainers:
    - name: initializer
      image: pratapgowda/demo-initializer
      imagePullPolicy: IfNotPresent # Pull images only if missing in the node, Defaulted to Always
      env: # Inject an environment variable directly through configuration
        - name: WAIT_IN_SECS
          value: "5"
      volumeMounts: # Mount a file system for temporary processing at given path
        - name: workdir
          mountPath: "/work-dir"
  containers:
    # A .Net blazor application hosted on port 8080
    - name: webapp
      image: pratapgowda/demo-webapp:1.0
      imagePullPolicy: IfNotPresent # Pull images only if missing in the node
      ports:
        - containerPort: 8080 # exposed ports
      volumeMounts: # Mount a file system for temporary processing at given path
        - name: workdir
          mountPath: /usr/share/webapp/html
      resources: 
        limits: # Maximum limits for the resource utilization
          cpu: "500m" # When container reaches the limit, k8s throttles the CPU slice
          memory: 1G  # When container consumes more than the limit memory, its premptively removed as OOMKilled status 
        requests: # If node doesnt have the below requirements, pod would be in pending state till available.
          cpu: "250m" # Minimum allocation of the CPU, k8s guarantees this amount from the node.
          memory: 100Mi # Minimum allocation of the memory, k8s guarantees this amount from the node.
      livenessProbe: # A Health probe from the container, could be an HTTP/TCP/gRPC(beta) endpoint or even a command
        httpGet:  # If the probe fails to be successful, the container would be deemed unhealthy and the pod would be restarted.
          path: /health
          port: 8080
        initialDelaySeconds: 3
        periodSeconds: 3
      readinessProbe: # A Probe to allow traffic to the container, if the probe fails traffic will not be routed through a service to this pod 
        httpGet:
          path: /health
          port: 8080
        initialDelaySeconds: 3
        periodSeconds: 3
    # A Simple container running parellely within the same pod to show case how then can talk to each other
    - name: sidecar
      image: busybox # by default dockerhub and latest tags are considered
      imagePullPolicy: IfNotPresent # Pull images only if missing in the node
      resources:
        limits:
          cpu: "500m"
          memory: 1G
        requests:
          cpu: "250m"
          memory: 100Mi
      command: # Execute a command once the container is loaded
        - sleep
        - "6000"
  volumes: # An empty ephemral directory definition to be mounted into the containers
    - name: workdir
      emptyDir: {}