Feature flags in Kubernetes - Mini Project: Build & Apply

Feature Flags in Kubernetes

📖 Scenario: You are managing a Kubernetes deployment for a web application. You want to control a new feature rollout using feature flags. This means you can turn the feature on or off without changing the application code or redeploying.Feature flags will be stored as environment variables in the deployment manifest. You will create a ConfigMap to hold the feature flag, then update the deployment to use this flag.

🎯 Goal: Build a Kubernetes ConfigMap to store a feature flag, then update a Deployment to use this flag as an environment variable. Finally, check the pod environment to confirm the flag is set.

📋 What You'll Learn

Create a ConfigMap named feature-flags with a key NEW_FEATURE_ENABLED set to "false"

Update the Deployment named web-app to add an environment variable NEW_FEATURE_ENABLED from the ConfigMap

Verify the pod environment variable NEW_FEATURE_ENABLED is set correctly

💡 Why This Matters

🌍 Real World

Feature flags help teams release new features safely by enabling or disabling them dynamically in Kubernetes environments.

💼 Career

DevOps engineers often manage feature flags via ConfigMaps and environment variables to control application behavior without redeploying.

1

Create the ConfigMap for feature flags

Create a Kubernetes ConfigMap named feature-flags with a key NEW_FEATURE_ENABLED set to the string "false". Use the kubectl create configmap command with the literal flag.

Kubernetes

# Your command here to create the ConfigMap
# Example: kubectl create configmap feature-flags --from-literal=NEW_FEATURE_ENABLED=false

Need a hint?

Use kubectl create configmap feature-flags --from-literal=NEW_FEATURE_ENABLED=false to create the ConfigMap.

2

Add environment variable from ConfigMap to Deployment

Edit the Deployment named web-app to add an environment variable NEW_FEATURE_ENABLED that gets its value from the ConfigMap feature-flags. Use kubectl patch deployment web-app with a JSON patch to add the environment variable under spec.template.spec.containers[0].env.

Kubernetes

kubectl create configmap feature-flags --from-literal=NEW_FEATURE_ENABLED=false
# Your command here to patch the deployment to add the env var

Need a hint?

Use a JSON patch to add the environment variable from the ConfigMap to the first container in the deployment.

3

Check the pod environment variable

Get the name of one pod from the web-app deployment using kubectl get pods with a label selector. Then use kubectl exec to run printenv NEW_FEATURE_ENABLED inside the pod to check the environment variable value.

Kubernetes

kubectl create configmap feature-flags --from-literal=NEW_FEATURE_ENABLED=false
kubectl patch deployment web-app --type='json' -p='[{"op": "add", "path": "/spec/template/spec/containers/0/env", "value": [{"name": "NEW_FEATURE_ENABLED", "valueFrom": {"configMapKeyRef": {"name": "feature-flags", "key": "NEW_FEATURE_ENABLED"}}}]}]'
# Your commands here to get a pod name and print the environment variable

Need a hint?

Use kubectl get pods -l app=web-app -o jsonpath='{.items[0].metadata.name}' to get the pod name, then kubectl exec to run printenv NEW_FEATURE_ENABLED.

4

Display the feature flag value

Print the output of the environment variable NEW_FEATURE_ENABLED from the pod. This should show false as the current feature flag value.

Kubernetes

kubectl create configmap feature-flags --from-literal=NEW_FEATURE_ENABLED=false
kubectl patch deployment web-app --type='json' -p='[{"op": "add", "path": "/spec/template/spec/containers/0/env", "value": [{"name": "NEW_FEATURE_ENABLED", "valueFrom": {"configMapKeyRef": {"name": "feature-flags", "key": "NEW_FEATURE_ENABLED"}}}]}]'
POD_NAME=$(kubectl get pods -l app=web-app -o jsonpath='{.items[0].metadata.name}')
kubectl exec $POD_NAME -- printenv NEW_FEATURE_ENABLED
# Run the command above and observe the output

Need a hint?

The output should be exactly false, showing the feature flag is off.