Incremental migration plan in Microservices - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is an incremental migration plan in microservices?

An incremental migration plan breaks down the move from a monolithic system to microservices into small, manageable steps. It allows gradual transition without stopping the whole system.

beginner

Why is incremental migration preferred over a big bang migration?

Incremental migration reduces risk by allowing testing and validation at each step. It avoids system downtime and lets teams fix issues early before moving on.

intermediate

Name a common strategy used in incremental migration plans.

The strangler pattern is common. It gradually replaces parts of the old system with new microservices until the old system is fully replaced.

intermediate

What role does API gateway play in incremental migration?

An API gateway routes requests between old and new services during migration. It helps manage traffic and ensures smooth communication.

advanced

How do you handle data consistency during incremental migration?

Data consistency is handled by synchronizing databases or using event-driven communication to keep data updated across old and new services.

What is the main benefit of an incremental migration plan?

A Eliminates need for new services

B Completes migration in one step

C Requires no testing

D Reduces risk by gradual transition

Incremental migration reduces risk by allowing gradual transition and testing at each step.

Which pattern is commonly used in incremental migration?

A Singleton pattern

B Factory pattern

C Strangler pattern

D Observer pattern

The strangler pattern gradually replaces parts of the old system with new microservices.

During incremental migration, what component manages routing between old and new services?

A Database

B API gateway

C Load balancer

D Cache

API gateway routes requests between old and new services during migration.

How is data consistency maintained during incremental migration?

A Synchronizing databases or event-driven updates

B Ignoring old data

C Using only one database

D Manual data entry

Data consistency is maintained by synchronizing databases or using event-driven communication.

What is a risk of big bang migration compared to incremental migration?

A High risk of system downtime

B Easier testing

C Lower cost

D Faster deployment

Big bang migration risks system downtime due to all changes happening at once.

Explain the steps involved in an incremental migration plan for microservices.

Think about how to move from old to new system safely and gradually.

Describe how data synchronization can be achieved during incremental migration.

Consider how data stays accurate when two systems run together.

Practice

1. What is the main goal of an incremental migration plan in microservices?

easy

A. To avoid testing during migration

B. To rewrite the entire system at once

C. To remove all old services immediately

D. To move functionality step-by-step to reduce risk

Solution

1. Step 1: Understand migration goals

   Incremental migration aims to reduce risk by breaking changes into small steps.

2. Step 2: Compare options

   Options B, C, and D involve big changes or skipping testing, which increase risk.

3. Final Answer:

   To move functionality step-by-step to reduce risk -> Option D

4. Quick Check:

   Incremental migration = step-by-step safe moves [OK]

Hint: Think small safe steps, not big risky jumps [OK]

Common Mistakes:

• Assuming migration happens all at once
• Ignoring the need for testing
• Believing old services must be removed immediately

2. Which of the following is a correct step in an incremental migration plan?

easy

A. Deploy all new microservices simultaneously without routing changes

B. Use feature flags or routing to direct some traffic to new services

C. Stop the old system before starting migration

D. Skip monitoring during migration to save resources

Solution

1. Step 1: Identify safe deployment practices

   Using feature flags or routing allows gradual traffic shift to new services safely.

2. Step 2: Eliminate unsafe options

   Deploying all at once, stopping old system early, or skipping monitoring are risky.

3. Final Answer:

   Use feature flags or routing to direct some traffic to new services -> Option B

4. Quick Check:

   Routing traffic gradually = safe migration [OK]

Hint: Use routing or flags to control traffic flow [OK]

Common Mistakes:

• Deploying everything at once
• Stopping old system too early
• Ignoring monitoring during migration

3. Consider this migration step code snippet for routing traffic:

if (user.isBetaTester) {
  routeToNewService();
} else {
  routeToOldService();
}

What will happen if a user is not a beta tester?

medium

A. User traffic is dropped

B. User traffic goes to the new service

C. User traffic goes to the old service

D. User traffic causes an error

Solution

1. Step 1: Analyze the condition

   If user.isBetaTester is false, the else branch runs.

2. Step 2: Determine routing for else branch

   The else branch calls routeToOldService(), so traffic goes to old service.

3. Final Answer:

   User traffic goes to the old service -> Option C

4. Quick Check:

   Non-beta users = old service routing [OK]

Hint: False condition triggers else branch routing [OK]

Common Mistakes:

• Assuming all users go to new service
• Thinking traffic is dropped or errors occur
• Ignoring the else branch logic

4. A team started migrating a service incrementally but suddenly disabled monitoring. What is the likely problem?

medium

A. They lose visibility into errors and performance

B. They can detect issues faster

C. Migration speed increases without risks

D. Old services automatically update

Solution

1. Step 1: Understand monitoring role

   Monitoring helps detect errors and performance issues during migration.

2. Step 2: Assess impact of disabling monitoring

   Without monitoring, the team loses visibility into problems, increasing risk.

3. Final Answer:

   They lose visibility into errors and performance -> Option A

4. Quick Check:

   No monitoring = no error visibility [OK]

Hint: Never disable monitoring during migration [OK]

Common Mistakes:

• Assuming disabling monitoring improves speed
• Thinking old services update automatically
• Believing issues are easier to detect without monitoring

5. You plan to migrate a monolith to microservices incrementally. Which approach best ensures minimal downtime and rollback capability?

hard

A. Deploy new microservices behind a feature flag and route a small % of traffic gradually

B. Replace the monolith entirely in one deployment window

C. Migrate database schema all at once without backward compatibility

D. Disable old services immediately after deploying new ones

Solution

1. Step 1: Evaluate migration strategies

   Deploying behind feature flags and routing small traffic allows gradual testing and rollback.

2. Step 2: Compare risks of other options

   Replacing all at once or disabling old services causes downtime; schema changes without compatibility break systems.

3. Final Answer:

   Deploy new microservices behind a feature flag and route a small % of traffic gradually -> Option A

4. Quick Check:

   Feature flags + gradual traffic = safe migration [OK]

Hint: Use feature flags and gradual traffic shift for safety [OK]

Common Mistakes:

• Trying big-bang replacement causing downtime
• Ignoring backward compatibility in database changes
• Disabling old services too early