Feature flags in Microservices - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to check if a feature is enabled before executing it.

Microservices

if feature_flags.is_enabled([1]):
    execute_new_feature()

Drag options to blanks, or click blank then click option'

ATrue

Bnew_ui

Cfeature_name

D"new_ui"

Attempts:

3 left

💡 Hint

Common Mistakes

Passing the feature flag name without quotes causing a NameError.

Passing a boolean value instead of the feature flag name.

The feature flag name must be passed as a string to check if it is enabled.

2fill in blank

medium

Complete the code to fetch the feature flag status from the config service.

Microservices

status = config_service.get_flag_status([1])

Drag options to blanks, or click blank then click option'

A"beta_feature"

Bfeature_id

CTrue

Dflag_status

Attempts:

3 left

💡 Hint

Common Mistakes

Passing a variable name instead of a string literal.

Using boolean values instead of flag names.

The feature flag identifier should be a string representing the flag name.

3fill in blank

hard

Fix the error in the code that updates a feature flag status.

Microservices

feature_flags.update_flag([1], True)

Drag options to blanks, or click blank then click option'

A123

B"new_feature"

CTrue

Dflag_enabled

Attempts:

3 left

💡 Hint

Common Mistakes

Passing an integer instead of a string as the flag name.

Passing a boolean instead of the flag name.

The feature flag name must be a string to correctly identify which flag to update.

4fill in blank

hard

Fill both blanks to create a dictionary of feature flags with their enabled status.

Microservices

flags = [1](flag: feature_flags.[2](flag) for flag in all_flags)

Drag options to blanks, or click blank then click option'

Adict

Bis_enabled

Clist

Dget_status

Attempts:

3 left

💡 Hint

Common Mistakes

Using list instead of dict causing wrong data structure.

Using a wrong method name to check flag status.

Use dict to create a dictionary and is_enabled to check each flag's status.

5fill in blank

hard

Fill all three blanks to filter enabled features and store their names in a list.

Microservices

enabled_features = [flag for flag in all_flags if feature_flags.[1](flag) [2] [3]]

Drag options to blanks, or click blank then click option'

Ais_enabled

B==

CTrue

Dget_flag

Attempts:

3 left

💡 Hint

Common Mistakes

Using assignment = instead of comparison ==.

Comparing with False instead of True.

Use is_enabled to check the flag, compare it with True using == to filter enabled flags.

Practice

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

easy

A. To increase database storage capacity

B. To enable or disable features without deploying new code

C. To improve network bandwidth

D. To encrypt communication between services

Solution

1. Step 1: Understand feature flags concept

   Feature flags allow toggling features on or off dynamically without changing the codebase.

2. Step 2: Identify the main benefit in microservices

   This helps in testing, gradual rollout, and quick disabling of features without redeployment.

3. Final Answer:

   To enable or disable features without deploying new code -> Option B

4. Quick Check:

   Feature flags = toggle features dynamically [OK]

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

Common Mistakes:

• Confusing feature flags with database scaling
• Thinking feature flags improve network speed
• Assuming feature flags handle encryption

2. Which of the following is the correct way to check a feature flag named new_ui_enabled in a microservice?

easy

A. featureFlags.enable('new_ui_enabled')

B. if (featureFlags.check('new_ui_enabled') == false) { /* use new UI */ }

C. if (featureFlags.isEnabled('new_ui_enabled')) { /* use new UI */ }

D. featureFlags.remove('new_ui_enabled')

Solution

1. Step 1: Identify correct method to check flag status

   Checking if a feature flag is enabled usually uses a method like isEnabled returning true or false.

2. Step 2: Analyze options

   if (featureFlags.isEnabled('new_ui_enabled')) { /* use new UI */ } correctly checks if the flag is enabled before using the feature. if (featureFlags.check('new_ui_enabled') == false) { /* use new UI */ } incorrectly uses check and false condition. featureFlags.enable('new_ui_enabled') and featureFlags.remove('new_ui_enabled') modify flags, not check them.

3. Final Answer:

   if (featureFlags.isEnabled('new_ui_enabled')) { /* use new UI */ } -> Option C

4. Quick Check:

   Check flag with isEnabled() = if (featureFlags.isEnabled('new_ui_enabled')) { /* use new UI */ } [OK]

Hint: Use isEnabled() to check feature flags status [OK]

Common Mistakes:

• Using enable() or remove() to check flags
• Checking flag with wrong method or negation
• Confusing flag check with flag update

3. Consider this pseudocode snippet in a microservice:

if (featureFlags.isEnabled('beta_feature')) {
  return 'Beta feature active';
} else {
  return 'Beta feature inactive';
}

What will be the output if the flag beta_feature is set to false?

medium

A. Beta feature inactive

B. Beta feature active

C. Error: flag not found

D. No output

Solution

1. Step 1: Understand flag value effect on condition

   The condition checks if beta_feature is enabled (true). If false, it goes to else branch.

2. Step 2: Determine output when flag is false

   Since the flag is false, the else block executes returning 'Beta feature inactive'.

3. Final Answer:

   Beta feature inactive -> Option A

4. Quick Check:

   Flag false triggers else = Beta feature inactive [OK]

Hint: False flag runs else block output [OK]

Common Mistakes:

• Assuming false flag runs if block
• Expecting error when flag is false
• Ignoring else branch output

4. A developer wrote this code to disable a feature using a feature flag:

if (featureFlags.isEnabled('dark_mode')) {
  disableDarkMode();
}

Why might this code not work as intended?

medium

A. It disables dark mode when the flag is enabled, which is opposite logic

B. The method disableDarkMode() does not exist

C. Feature flags cannot control UI features

D. The flag name should be 'enable_dark_mode'

Solution

1. Step 1: Analyze the condition logic

   The code disables dark mode if the flag is enabled, which is opposite of expected behavior (usually enabled flag means enable feature).

2. Step 2: Identify correct logic for disabling feature

   To disable dark mode when flag is false, the condition should check if flag is disabled or negate the check.

3. Final Answer:

   It disables dark mode when the flag is enabled, which is opposite logic -> Option A

4. Quick Check:

   Enabled flag should enable, not disable [OK]

Hint: Enabled flag usually means feature ON, not OFF [OK]

Common Mistakes:

• Confusing enable and disable logic
• Assuming flag controls only backend features
• Using wrong flag names without checking

5. You want to roll out a new payment feature gradually using feature flags in a microservices system. Which design approach is best to ensure minimal impact and easy rollback?

hard

A. Disable all other microservices during rollout to avoid conflicts

B. Deploy new code with feature always enabled and monitor logs manually

C. Hardcode feature flag values in each microservice and update code to change flags

D. Use a centralized feature flag service with percentage rollout and fallback to old payment service

Solution

1. Step 1: Understand gradual rollout with feature flags

   Gradual rollout means enabling feature for a small percentage of users first, then increasing over time.

2. Step 2: Identify scalable and safe design

   A centralized flag service allows dynamic control and percentage rollout. Fallback ensures quick rollback if issues arise.

3. Step 3: Evaluate other options

   Deploy new code with feature always enabled and monitor logs manually lacks control and rollback ease. Hardcode feature flag values in each microservice and update code to change flags requires code changes for flag updates, not scalable. Disable all other microservices during rollout to avoid conflicts is disruptive and unnecessary.

4. Final Answer:

   Use a centralized feature flag service with percentage rollout and fallback to old payment service -> Option D

5. Quick Check:

   Centralized flags + gradual rollout = Use a centralized feature flag service with percentage rollout and fallback to old payment service [OK]

Hint: Centralized flags + gradual rollout = safe deployment [OK]

Common Mistakes:

• Hardcoding flags causing frequent deployments
• Disabling services unnecessarily during rollout
• Ignoring rollback strategies