kubernetes Deployment. how to change container environment variables for rolling updates?

Question

Below is how I am using kunbernetes on google.

I have one node application let's say Book-portal.

node app is using environment variables for configurations.

Step1: I created docker file and pushed

gcr.io/<project-id>/book-portal:v1

Step2: deployed with following commands

kubectl run book-portal --image=gcr.io/<project-id>/book-portal:v1 --port=5555 --env ENV_VAR_KEY1=value1 --env ENV_VAR_KEY2=value2 --env ENV_VAR_KEY3=value3

Step3:

kubectl expose deployment book-portal --type="LoadBalancer"

Step4: Get public ip with

kubectl get services book-portal

now assume I added new features and new configurations in next release.

So to roll out new version v2

Step1: I created docker file and pushed

gcr.io/<project-id>/book-portal:v2

Step2: Edit deployment

kubectl edit deployment book-portal

---------------yaml---------------
...
    spec:
      replicas: 1
      selector:
        matchLabels:
          run: book-portal
      strategy:
        rollingUpdate:
          maxSurge: 1
          maxUnavailable: 1
        type: RollingUpdate
      template:
        metadata:
          creationTimestamp: null
          labels:
            run: book-portal
        spec:
          containers:
          - env:
            - name: ENV_VAR_KEY1
              value: value1
            - name: ENV_VAR_KEY2
              value: value2
            - name: ENV_VAR_KEY3
              value: value3
            image: gcr.io/<project-id>/book-portal:v1
            imagePullPolicy: IfNotPresent
            name: book-portal
...
----------------------------------

I am successfully able to change

image:gcr.io/<project-id>/book-portal:v1 

to

image:gcr.io/<project-id>/book-portal:v2 

But I can not add/change environment variables

          - env:
            - name: ENV_VAR_KEY1
              value: value1
            - name: ENV_VAR_KEY2
              value: value2
            - name: ENV_VAR_KEY3
              value: value3
            - name: ENV_VAR_KEY4
              value: value4

1. Can anyone guide with what is best practices to pass configurations in node app on kubernetes?
2. how should I handle environment variable changes during rolling updates?

Answer 1

I think your best bet is to use configmaps in k8s and then change you pod template to get env variable values from the configmap see Consuming ConfigMap in pods

edit: I appologize I put the wrong link here. I have updated but for the TL;DR you can do the following.

apiVersion: v1
kind: ConfigMap
metadata:
 name: special-config
namespace: default
data:
 special.how: very
 special.type: charm

and then pod usage can look like this.

apiVersion: v1
kind: Pod
metadata:
 name: dapi-test-pod
spec:
  containers:
  - name: test-container
    image: gcr.io/google_containers/busybox
    command: [ "/bin/sh", "-c", "env" ]
    env:
      - name: SPECIAL_LEVEL_KEY
        valueFrom:
          configMapKeyRef:
            name: special-config
            key: special.how
      - name: SPECIAL_TYPE_KEY
        valueFrom:
          configMapKeyRef:
            name: special-config
            key: special.type
  restartPolicy: Never