container initialization order in pod on K8s-CodePudding

I want to run tow containers on single pod. container1 is a test that tries to connect to a SQL Server Database that runs on container2. How can I make sure that the sql container(container2) will run and be ready before container1 starts?

initContainer won't work here, as it will run before both containers

this is my compose.yaml:

apiVersion: v1
kind: Pod
metadata:
  name: sql-test-pod
  labels:
    name: sql-test
spec:
  restartPolicy: Never
  containers:
    - name: my-sqldb
      image: docker-registry.com/database
      imagePullPolicy: Always
      resources:
        limits:
          memory: "4096Mi"
          cpu: "750m"
        requests:
          memory: "4096Mi"
          cpu: "750m"
    - name: tests
      tty: true
      stdin: true
      image: docker-registry.com/test
      imagePullPolicy: Always
      resources:
        limits:
          memory: "4096Mi"
          cpu: "750m"
        requests:
          memory: "4096Mi"
          cpu: "750m"
      env:
      - name: sqlhostname
        value: "SqlHostnamePlaceholder"
  nodeSelector:
    kubernetes.io/os: windows
  tolerations:
  - key: "windows"
    operator: "Equal"
    value: "2019"
    effect: "NoSchedule"

CodePudding user response：

You cannot do that with current implements of kubernetes: all container in one pod will startup in same time(except the init container).

One solution is to enhance the code in test container to detect the state of db container, hold on until is ready.

CodePudding user response：

Another option is to add command and args to the container.

You can add sleep command if it's known approximate time for another container to start or add some logic within the command (while loop checking the connection, once it's connected, exit the loop and run main process - example).

Note! Image's entrypoint will be replaced by this command:

The command and arguments that you define in the configuration file override the default command and arguments provided by the container image

For instance, for nginx and command container spec will look like (since entrypoint is replaced, it's necessary to provide a command to start the nginx server):

  containers:
    - name: test
      image: nginx
      command: ["/bin/bash", "-c"]
      args: ["sleep 30 ; echo sleep ended ;  nginx -g \"daemon off;\""]

More details here Define a Command and Arguments for a Container.