Feature flags in Kubernetes - Commands & Configuration

Introduction

Feature flags let you turn parts of your app on or off without changing code. In Kubernetes, you can use ConfigMaps to manage these flags easily and update your app behavior without redeploying.

When you want to enable a new feature for testing without redeploying your app

When you need to quickly disable a feature causing issues in production

When you want to gradually roll out a feature to some users by changing config

When you want to keep one app version but change behavior based on flags

When you want to separate feature control from app code for easier updates

Config File - feature-flags-configmap.yaml

feature-flags-configmap.yaml

apiVersion: v1
kind: ConfigMap
metadata:
  name: feature-flags
  namespace: default
data:
  newFeatureEnabled: "true"
  betaFeature: "false"

This ConfigMap stores feature flags as key-value pairs.

newFeatureEnabled controls if the new feature is active.

betaFeature controls a beta feature toggle.

Your app reads these values to decide which features to run.

Commands

Create or update the ConfigMap with feature flags in Kubernetes.

Terminal

kubectl apply -f feature-flags-configmap.yaml

Expected Output

configmap/feature-flags created

Check the current feature flags stored in the ConfigMap.

Terminal

kubectl get configmap feature-flags -o yaml

Expected Output

apiVersion: v1

data:

  betaFeature: "false"

  newFeatureEnabled: "true"

kind: ConfigMap

metadata:

  name: feature-flags

  namespace: default

  resourceVersion: "12345"

  uid: abcdef12-3456-7890-abcd-ef1234567890

→

-o yaml - Outputs the ConfigMap in YAML format for easy reading

Restart the app deployment to pick up updated feature flags if your app reads them on startup.

Terminal

kubectl rollout restart deployment my-app

Expected Output

deployment.apps/my-app restarted

View detailed information about the feature flags ConfigMap.

Terminal

kubectl describe configmap feature-flags

Expected Output

Name:         feature-flags

Namespace:    default

Labels:       <none>

Annotations:  <none>

Data

====

betaFeature:

false

newFeatureEnabled:

true

Events:       <none>

Key Concept

If you remember nothing else from this pattern, remember: use ConfigMaps to store feature flags so you can change app behavior without changing code or rebuilding images.

Common Mistakes

Changing the ConfigMap but not restarting the app pods

The app may not reload the new flags until restarted, so changes have no effect.

Restart the deployment or pods after updating the ConfigMap if your app reads flags only on startup.

Storing feature flags inside the app code instead of ConfigMaps

You lose flexibility to toggle features without redeploying the app.

Use ConfigMaps to separate feature flags from code for easy updates.

Using non-string values in ConfigMap data

ConfigMap data must be strings; other types cause errors or unexpected behavior.

Always store feature flag values as strings like "true" or "false".

Summary

Create a ConfigMap to hold feature flags as key-value pairs.

Apply the ConfigMap with kubectl apply -f to create or update it.

Check the ConfigMap contents with kubectl get or describe commands.

Restart your app deployment to apply new flags if your app reads them on startup.

Practice

1. What is the main purpose of feature flags in Kubernetes?

easy

A. To manage Kubernetes cluster nodes

B. To monitor cluster health

C. To schedule pods across nodes

D. To enable or disable application features without changing code

Solution

1. Step 1: Understand feature flags concept

   Feature flags allow toggling features on or off without modifying the application code.

2. Step 2: Relate to Kubernetes usage

   In Kubernetes, feature flags help control app behavior dynamically, often via ConfigMaps or environment variables.

3. Final Answer:

   To enable or disable application features without changing code -> Option D

4. Quick Check:

   Feature flags = toggle features without code change [OK]

Hint: Feature flags toggle features without code edits [OK]

Common Mistakes:

• Confusing feature flags with cluster management
• Thinking feature flags manage pods or nodes
• Mixing feature flags with monitoring tools

2. Which Kubernetes resource is commonly used to store feature flags for an application?

easy

A. Service

B. Pod

C. ConfigMap

D. Ingress

Solution

1. Step 1: Identify resource types

   Pods run containers, Services expose them, Ingress manages external access, ConfigMaps store configuration data.

2. Step 2: Match feature flags storage

   Feature flags are configuration data, so ConfigMaps are the right resource to store them.

3. Final Answer:

   ConfigMap -> Option C

4. Quick Check:

   Feature flags stored in ConfigMap [OK]

Hint: ConfigMaps hold config data like feature flags [OK]

Common Mistakes:

• Choosing Pod instead of ConfigMap
• Confusing Service or Ingress with config storage
• Thinking feature flags are stored in Secrets

3. Given this ConfigMap YAML snippet for feature flags:

apiVersion: v1
kind: ConfigMap
metadata:
  name: feature-flags
data:
  FEATURE_X_ENABLED: "true"
  FEATURE_Y_ENABLED: "false"

What will be the value of FEATURE_Y_ENABLED when accessed as an environment variable in a pod?

medium

A. false

B. true

C. null

D. undefined

Solution

1. Step 1: Read ConfigMap data values

   The ConfigMap sets FEATURE_Y_ENABLED to the string "false" explicitly.

2. Step 2: Understand environment variable mapping

   When injected as env vars, values are strings exactly as in ConfigMap, so FEATURE_Y_ENABLED will be "false".

3. Final Answer:

   false -> Option A

4. Quick Check:

   ConfigMap value "false" = env var "false" [OK]

Hint: Env vars get exact string values from ConfigMap [OK]

Common Mistakes:

• Assuming boolean false instead of string "false"
• Thinking missing keys return null or undefined
• Confusing string values with boolean types

4. You have this environment variable setup in a pod spec:

- name: FEATURE_Z_ENABLED
  valueFrom:
    configMapKeyRef:
      name: feature-flags
      key: FEATURE_Z_ENABLED

If the ConfigMap 'feature-flags' does not have the key FEATURE_Z_ENABLED, what will happen when the pod starts?

medium

A. Pod will fail to start with an error

B. Pod will start with FEATURE_Z_ENABLED set to an empty string

C. Pod will start with FEATURE_Z_ENABLED set to null

D. Pod will ignore the environment variable

Solution

1. Step 1: Understand configMapKeyRef behavior

   If the specified key is missing in the ConfigMap, Kubernetes treats it as an error.

2. Step 2: Effect on pod startup

   The pod will fail to start because the environment variable cannot be resolved from the ConfigMap key.

3. Final Answer:

   Pod will fail to start with an error -> Option A

4. Quick Check:

   Missing ConfigMap key causes pod start failure [OK]

Hint: Missing ConfigMap key breaks pod start [OK]

Common Mistakes:

• Assuming empty string or null is set silently
• Thinking pod ignores missing keys
• Confusing with optional environment variables

5. You want to enable a new feature only for 10% of users using feature flags in Kubernetes. Which approach best supports this scenario?

hard

A. Use a ConfigMap with a boolean flag set to true or false

B. Store a percentage value in ConfigMap and let the app decide feature enablement per user

C. Use a Secret to store the feature flag and update it daily

D. Deploy two versions of the app and route 10% traffic to the new version

Solution

1. Step 1: Understand percentage-based feature flags

   To enable a feature for a subset of users, the flag must support partial enablement, not just true/false.

2. Step 2: Evaluate options

   Store a percentage value in ConfigMap and let the app decide feature enablement per user stores a percentage in ConfigMap; the app reads it and enables the feature for that percent of users dynamically.

3. Final Answer:

   Store a percentage value in ConfigMap and let the app decide feature enablement per user -> Option B

4. Quick Check:

   Percentage flags need app logic with ConfigMap value [OK]

Hint: Use percentage value in ConfigMap for partial rollout [OK]

Common Mistakes:

• Using boolean flags for partial user enablement
• Relying on Secrets for feature flags
• Thinking traffic routing replaces feature flags