This is a very simple task. However one I occasionally get the syntax wrong for.

The scenario is you need to modify the environmental variable of a Kubernetes Pod/Deployment. In order to do this you must edit the Deployment. Once this is saved a new pod is spawned and the old pod is terminated. This is repeated until all pods have been updated. When modifying the deployment if you create a syntax error k8s does not save the config change.

It is recommend to do this at the deploy level not the pod level so the changes are persisted.

Step 1 Run the following

kubectl edit deploy <deployment name> -n  <namespace>

Where deployment name is the name of the deployment you wish to change and namespaces is the namespace contianing the deployment.

Step 2 Go to the env section of the deployment config. If there is not an env section you can create one using with the key env: in each entry of the containers array.

apiVersion: apps/v1
kind: Deployment
metadata:
  name: nginx-deployment
  labels:
    app: nginx
spec:
  replicas: 3
  selector:
    matchLabels:
      app: nginx
  template:
    metadata:
      labels:
        app: nginx
    spec:
      containers:
      - name: nginx
        image: nginx:1.7.9
        ports:
        - containerPort: 80

Step 3 Add the variable using the following format. Ensure that the number of spaces is correct and it is added after the env: line.

- name: DEMO_FAREWELL
  value: "Such a sweet sorrow"

This should look similar to the below.

apiVersion: apps/v1
kind: Deployment
metadata:
  name: nginx-deployment
  labels:
    app: nginx
spec:
  replicas: 3
  selector:
    matchLabels:
      app: nginx
  template:
    metadata:
      labels:
        app: nginx
    spec:
      containers:
      - name: nginx
        image: nginx:1.7.9
        ports:
        - containerPort: 80
        env:
        - name: DEMO_GREETING
          value: "Hello from the environment"
        - name: DEMO_FAREWELL
          value: "Such a sweet sorrow"

Step 4 Save the file

If the file does not exit cleanly it is because Kubernetes thinks there was a syntax error and you must go and make your change again.

Step 5 Check the pods are being replaced, by running the following command

kubectl get po -n <namespace>  -w

-w triggers the watch function of Kubernetes. When you have finished watching press ctrl + c to exit.

Samples taken from https://kubernetes.io