I would like to specify dependent environment variables on a Cloud Run service.

If the environment variables have been defined in a .env file it would look like this

DATABASE_NAME=my-database
DATABASE_USER=root
DATABASE_PASSWORD=P4SSw0rd!
DATABASE_PORT=5432
DATABASE_HOST="/socket/my-database-socket"
DATABASE_URL="user=${DATABASE_USER} password=${DATABASE_PASSWORD} dbname=${DATABASE_NAME} host=${DATABASE_HOST}"

In this example, DATABASE_URL depends on every other environment variables.

To deploy the service I run the following command:

gcloud run deploy my-service \
--image gcr.io/my-project/my-image:latest \
--region europe-west1 \
--port 80 \
--platform managed \
--allow-unauthenticated \
--set-env-vars 'DATABASE_NAME=my-database' \
--set-env-vars 'DATABASE_USER=root' \
--set-env-vars 'DATABASE_PASSWORD=P4SSw0rd!' \
--set-env-vars 'DATABASE_PORT=5432' \
--set-env-vars 'DATABASE_HOST="/socket/my-database-socket"' \
--set-env-vars 'DATABASE_URL="user=$(DATABASE_USER) password=$(DATABASE_PASSWORD) dbname=$(DATABASE_NAME) host=$(DATABASE_HOST)"'

Here is the created YAML definition of the service (some values are omitted)

apiVersion: serving.knative.dev/v1
kind: Service
metadata:
  name: my-service
spec:
  template:
    metadata:
      name: ...
    spec:
      containerConcurrency: 80
      timeoutSeconds: 300
      containers:
      - image: ...
        ports:
        - name: http1
          containerPort: 80
        env:
        - name: DATABASE_NAME
          value: my-database
        - name: DATABASE_USER
          value: root
        - name: DATABASE_PASSWORD
          value: P4SSw0rd!
        - name: DATABASE_HOST
          value: /socket/my-database-socket
        - name: DATABASE_URL
          value: user=$(DATABASE_USER) password=$(DATABASE_PASSWORD) dbname=$(DATABASE_NAME) host=$(DATABASE_HOST)

The problem is that when the service is running, the env vars in DATABASE_URL seem not interpolated.

I read that Kubernetes supports dependent env vars but I can't figure out how to make this run in Cloud Run.

I am wondering if it is supported in Cloud Run in the end.

It's likely this may work in Knative open source (which uses Kubernetes to execute pods) but not on Google Cloud Run (fully hosted), which runs on a proprietary execution engine.