Kubernetes Pods: Use environment variables to define arguments

2 min read | by Jordi Prats

When configuring command line arguments for containers we might need to be able to use certain values that might be elsewhere like the name of the current namespace.

We can use environment variables as the source of the information without having to write a wrappet to actually populate them

To do so we'll have to use the $() syntax, pleace notice how it's using parentheses instead of curly braces that you might be more familar. Then we just need to define the environment variable with whatever value we need. In this example we are using valueFrom to get the object's namespace:

kind: Deployment apiVersion: apps/v1 metadata:  name: test-env  labels:  app: test-env spec:  selector:  matchLabels:  app: test-env  replicas: 1  strategy:  type: RollingUpdate  template:  metadata:  labels:  app: test-env  spec:  containers:  - name: test-env  image: alpine:latest  imagePullPolicy: Always  command: ["echo"]  args:  - namespace=$(CURRENT_NAMESPACE)  env:  - name: CURRENT_NAMESPACE  valueFrom:  fieldRef:  fieldPath: metadata.namespace 

Once we apply it we will be able to see how the value have been populated:

$ kubectl apply -f test_env.yaml deployment.apps/test-env created $ kubectl get pods NAME READY STATUS RESTARTS AGE test-env-9499cdd8c-7jwsd 0/1 ContainerCreating 0 5s $ kubectl logs test-env-9499cdd8c-7jwsd namespace=test-pet2cattle 

We can use this not only on a Deployment as we did on the example, but on any Pod template we need.

Posted on 26/08/2022