Passing variables to a container on startup

Question

I want to setup my Django app in kubernetes environment in such a way that while creating the app container, environment variables are passed such that those environment variables are used to initiate the containers. For example on starting the app container I want to issue management commands such as

python manage.py createuser --lastname lname --firstname --fname --number --num "

and so on. How to pass these variable values such as lname and fname above inside the container in a generic way such that every time new values can be passed depending on the user credentials and they do not need to be hard coded everytime?

You should be able to do this as a script that runs as container startup time, possibly an entrypoint wrapper script. What have you already tried? (Outside of Docker, could you write a script that did what you wanted and then launched the Django application?) — David Maze, Nov 04 '20 at 14:38
yes i run a shell script that quries the database pod as: kubectl exec -it database-pod -- bash -c "psql -U postgres -c \"Select json_build_object('first_name',first_name,'last_name',last_name,'email',email,'date_joined',date_joined) — devcloud, Nov 04 '20 at 15:12
I want to use the values returned by this shell script to initialize the container such as lastname etc — devcloud, Nov 04 '20 at 15:14

score 1 · Answer 1 · answered Nov 04 '20 at 14:38

You can pass environment variables in your deployment manifest, for example:

spec:
  containers:
  - name: envar-demo-container
    image: gcr.io/google-samples/node-hello:1.0
    env:
    - name: DEMO_GREETING
      value: "Hello from the environment"
    - name: DEMO_FAREWELL
      value: "Such a sweet sorrow"

You can also invoke them in container by using command and argument object, the same way as running a command in container

  containers:
  - name: env-print-demo
    image: bash
    env:
    - name: GREETING
      value: "Warm greetings to"
    - name: HONORIFIC
      value: "The Most Honorable"
    - name: NAME
      value: "Kubernetes"
    command: ["echo"]
    args: ["$(GREETING) $(HONORIFIC) $(NAME)"]

It is also possible to pass variables from ConfigMap or Secrets.

In my case i do not know the environment variables beforehand. The values need to be set as result of a bash script that gets values from querying a database pod. How to set the environment variable values dynamically? — devcloud, Nov 04 '20 at 15:20

Passing variables to a container on startup

1 Answers1