Supply Only Specific Environment Variables From ConfigMap¶

Consider a case where you want to use only a specific items from ConfigMap as environment variables instead of supplying entire ConfigMap as environment variables.

Let's see how we can do that.

Step 1: Create a ConfigMap¶

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apiVersion: v1
kind: ConfigMap
metadata:
  name: my-configmap
data:
  foo1: bar1
  foo2: bar2

Apply the manifest to create ConfigMap:

kubectl apply -f my-configmap.yml

Step 2: Verify ConfigMap¶

# List configmaps
kubectl get cm

# Describe the configmap
kubectl describe cm my-configmap

Step 3: Create Pods That Uses Environment Variables¶

Let's create pods that uses specific items from the ConfigMap as environment variables for the container. We'll use a deployment to create pods:

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apiVersion: apps/v1
kind: Deployment
metadata:
  name: my-deployment
spec:
  replicas: 1
  selector:
    matchLabels:
      app: nginx
  template:
    metadata:
      labels:
        app: nginx
    spec:
      containers:
      - name: nginx
        image: nginx
        env:
        - name: key1
          value: value1
        - name: key2
          value: value2
        - name: foo1
          valueFrom:
            configMapKeyRef:
              name: my-configmap
              key: foo1

Observe the following:

• We are using env keyword to supply a list of environment variables.
• We are also using valueFrom keyword to get the value of the key foo1 in the ConfigMap my-configmap and then setting it as the value of an environment variable named foo1.

Apply the manifest to create deployment:

kubectl apply -f my-deployment.yml

Step 4: Verify Deployment and Pods¶

# List deployments
kubectl get deployments

# List pods
kubectl get pods

Step 5: Verify Environment Variables¶

Start a shell session inside the container:

kubectl exec -it <pod-name> -- bash

List environment variables available to the container:

env

You'll see a list of environment variables available to the container. This includes both system-provided as well as user-provided (using env and valueFrom keyword) environment variables.

Print values of the environment variables we set:

# Print value of the environment variable key1
echo $key1

# Print value of the environment variable key2
echo $key2

# Print value of the environment variable foo1
echo $foo1

You'll notice the following:

• Environment variables key1 and key2 are set to value1 and value2 respectively.
• Environment variables foo1 is set to bar1.

Clean Up¶

Assuming your folder structure looks like the one below:

|-- manifests
│   |-- my-deployment.yml
│   |-- my-configmap.yml

Let's delete all the resources we created:

kubectl delete -f manifests/