Feature flags in Kubernetes - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

What is the primary purpose of feature flags in Kubernetes?

Feature flags are used in Kubernetes to:

A Increase the CPU and memory limits of pods dynamically

B Automatically scale pods based on network traffic

C Control the rollout of new features without redeploying the entire application

D Encrypt data stored in Kubernetes secrets

💡 Hint

Think about how you can enable or disable features without changing the app code or redeploying.

Feature flags allow toggling features on or off dynamically, enabling safer rollouts and testing without full redeployment.

💻 Command Output

intermediate

What is the output of this kubectl command?

Given a ConfigMap named feature-flags with a key newUI set to true, what does this command output?

kubectl get configmap feature-flags -o jsonpath='{.data.newUI}'

A false

B Error: configmap not found

C null

D true

💡 Hint

Check the key value inside the ConfigMap data field.

The command extracts the value of the newUI key from the ConfigMap data, which is true.

❓ Configuration

advanced

Which YAML snippet correctly defines a ConfigMap for feature flags with 'betaFeature' enabled?

Select the valid Kubernetes ConfigMap YAML that sets a feature flag betaFeature to enabled.

A

apiVersion: v1
kind: ConfigMap
metadata:
  name: feature-flags
data:
  - betaFeature: enabled

B

apiVersion: v1
kind: ConfigMap
metadata:
  name: feature-flags
data:
  betaFeature: enabled

C

apiVersion: v1
kind: ConfigMap
metadata:
  name: feature-flags
features:
  betaFeature: enabled

D

apiVersion: v1
kind: ConfigMap
metadata:
  name: feature-flags
spec:
  betaFeature: enabled

💡 Hint

ConfigMap data must be under the data field as key-value pairs.

Option B correctly uses the data field with key-value pairs. Other options misuse fields or structure.

🔀 Workflow

advanced

What is the correct sequence to update a feature flag in a running Kubernetes cluster?

Put these steps in the correct order to update a feature flag stored in a ConfigMap:

A 1,4,2,3

B 4,1,3,2

C 1,2,4,3

D 2,1,4,3

💡 Hint

Think about editing first, then saving, verifying, and finally ensuring pods use the new config.

You first edit the ConfigMap, save changes, verify the update, then ensure pods reload the new config.

❓ Troubleshoot

expert

Why might a pod not reflect a changed feature flag in a ConfigMap immediately?

You updated a feature flag in a ConfigMap, but the pod still behaves as if the old flag is active. What is the most likely reason?

A The pod has not been restarted or does not watch for ConfigMap changes

B The ConfigMap was deleted accidentally

C The feature flag key was misspelled in the ConfigMap

D The pod's CPU limit is too low to apply changes

💡 Hint

Consider how pods get updated ConfigMap data during runtime.

Pods do not automatically reload ConfigMap changes unless they watch for updates or are restarted.

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