Define an environment variable for a container

Question

I want to create a kubernetes pod and set the environment variables for the containers that run in the Pod  in a way that override any environment variables specified in the container image. How can i do this?

Answer 1

When you create a Pod, you can set environment variables for the containers that run in the Pod. 

To set environment variables, include the env or envFrom field in the configuration file.

Note: The environment variables set using the env or envFrom field will override any environment variables specified in the container image.

Example:  

Create a Pod that runs one container. 

The configuration file for the Pod defines an environment variable with name DEMO_GREETING and value "Hello from the environment". 

Here is the configuration file for the Pod:

pods/inject/envars.yaml 

apiVersion: v1
kind: Pod
metadata:
  name: envar-demo
  labels:
    purpose: demonstrate-envars
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"

1. Create a Pod based on the YAML configuration file: 

   kubectl apply -f https://k8s.io/examples/pods/inject/envars.yaml

2. List the running Pods:

   kubectl get pods -l purpose=demonstrate-envars
   
   

   The output is similar to this:

   NAME            READY     STATUS    RESTARTS   AGE
   envar-demo      1/1       Running   0          9s
   
   

3. Get a shell to the container running in your Pod:

   kubectl exec -it envar-demo -- /bin/bash
   

4. In your shell, run the printenv command to list the environment variables.

   root@envar-demo:/# printenv
   
   

   The output is similar to this:

   NODE_VERSION=4.4.2
   EXAMPLE_SERVICE_PORT_8080_TCP_ADDR=10.3.245.237
   HOSTNAME=envar-demo
   ...
   DEMO_GREETING=Hello from the environment
   DEMO_FAREWELL=Such a sweet sorrow

5. To exit the shell, enter exit.