Strangler fig pattern in Microservices - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the Strangler fig pattern in system design?

It is a method to gradually replace or modernize a legacy system by building a new system around it and slowly redirecting parts of the old system's functionality to the new one until the old system is fully replaced.

beginner

Why is the Strangler fig pattern named after a strangler fig tree?

Because just like the strangler fig tree grows around an old tree and eventually replaces it, this pattern grows a new system around the old one until the old system is no longer needed.

intermediate

What is a key benefit of using the Strangler fig pattern?

It allows safe, incremental migration without stopping the entire system, reducing risk and downtime during modernization.

intermediate

How does the Strangler fig pattern relate to microservices?

It helps break a monolithic legacy system into microservices step-by-step by redirecting specific features or modules to new microservices gradually.

advanced

What is a common challenge when implementing the Strangler fig pattern?

Managing data consistency and integration between the old and new systems during the transition phase can be complex.

What is the main goal of the Strangler fig pattern?

A Merge two unrelated systems

B Build a new system from scratch without old system

C Gradually replace a legacy system with a new system

D Keep the legacy system unchanged

The Strangler fig pattern focuses on gradually replacing the legacy system by building a new system around it.

Which analogy best describes the Strangler fig pattern?

A A tree growing around and replacing another tree

B A river splitting into two streams

C A bridge connecting two islands

D A house being painted a new color

The pattern is named after the strangler fig tree that grows around an old tree and eventually replaces it.

What is a key advantage of the Strangler fig pattern?

A Allows incremental migration with minimal downtime

B Requires complete system shutdown

C Eliminates need for testing

D Avoids any changes to legacy code

It enables gradual migration, reducing risk and downtime.

In microservices, how is the Strangler fig pattern typically used?

A By ignoring the legacy system

B By gradually redirecting features from monolith to microservices

C By rewriting the entire monolith at once

D By merging microservices into a monolith

It helps break down a monolith by incrementally moving features to microservices.

What is a common challenge when applying the Strangler fig pattern?

A Designing user interfaces

B Finding new developers

C Choosing a programming language

D Managing data consistency between old and new systems

Data consistency and integration during transition is often complex.

Explain the Strangler fig pattern and how it helps in modernizing legacy systems.

Think about how a new system grows around an old one like a tree.

Describe how the Strangler fig pattern can be applied to break a monolithic system into microservices.

Focus on moving parts step-by-step rather than all at once.

Practice

1. What is the main goal of the Strangler fig pattern in microservices architecture?

easy

A. To build all new services from scratch before replacing the old system

B. To merge all services into a single monolithic application

C. To run the old and new systems completely separately without integration

D. To gradually replace parts of a legacy system with new services

Solution

1. Step 1: Understand the pattern's purpose

   The Strangler fig pattern is designed to replace legacy systems gradually, not all at once.

2. Step 2: Compare options with the pattern goal

   To gradually replace parts of a legacy system with new services matches the gradual replacement approach, while others describe different strategies.

3. Final Answer:

   To gradually replace parts of a legacy system with new services -> Option D

4. Quick Check:

   Gradual replacement = B [OK]

Hint: Strangler fig means gradual replacement, not all at once [OK]

Common Mistakes:

• Thinking it replaces the whole system at once
• Confusing it with parallel running without integration
• Assuming it merges services into one

2. Which of the following is the correct way to route requests in the Strangler fig pattern?

easy

A. Send requests randomly to either legacy or new system without control

B. Direct all requests to the legacy system until the new system is fully ready

C. Route requests step-by-step from the legacy system to new microservices

D. Stop the legacy system completely before routing any requests

Solution

1. Step 1: Identify routing strategy in Strangler fig

   The pattern routes requests gradually from old to new components, not all at once or randomly.

2. Step 2: Match options with routing approach

   Route requests step-by-step from the legacy system to new microservices describes step-by-step routing, which fits the pattern best.

3. Final Answer:

   Route requests step-by-step from the legacy system to new microservices -> Option C

4. Quick Check:

   Step-by-step routing = A [OK]

Hint: Route requests gradually, not all or random [OK]

Common Mistakes:

• Routing all requests to legacy until full switch
• Routing requests randomly causing inconsistency
• Stopping legacy before new system ready

3. Consider this simplified request flow in a Strangler fig pattern:

Legacy system handles requests for features A, B, C.
New microservice replaces feature A.
Requests for A go to new service; B and C go to legacy.
What happens when a request for feature B arrives?

medium

A. It is routed to the new microservice handling feature A

B. It is routed to the legacy system since B is not replaced yet

C. It causes an error because feature B is missing in new service

D. It is dropped and not processed

Solution

1. Step 1: Analyze routing rules for features

   Only feature A is replaced by the new microservice; B and C remain in legacy.

2. Step 2: Determine routing for feature B request

   Requests for B still go to legacy system as it is not replaced yet.

3. Final Answer:

   It is routed to the legacy system since B is not replaced yet -> Option B

4. Quick Check:

   Feature B not replaced = legacy route = C [OK]

Hint: Unreplaced features stay on legacy system [OK]

Common Mistakes:

• Routing all requests to new service regardless of feature
• Assuming missing features cause errors
• Dropping requests instead of routing properly

4. A team tries to apply the Strangler fig pattern but routes all requests to the new microservice before it fully supports all features. What is the main problem with this approach?

medium

A. It leads to inconsistent behavior as new service lacks some features

B. It causes downtime because legacy system is stopped too early

C. It improves performance by forcing early migration

D. It simplifies deployment by removing legacy dependencies

Solution

1. Step 1: Identify issue with premature routing

   Routing all requests early means new service may not handle all features yet.

2. Step 2: Understand impact on system behavior

   This causes inconsistent or failed responses for unsupported features.

3. Final Answer:

   It leads to inconsistent behavior as new service lacks some features -> Option A

4. Quick Check:

   Premature routing = inconsistent behavior = A [OK]

Hint: Route only supported features to new service [OK]

Common Mistakes:

• Thinking early routing improves performance always
• Assuming legacy can be stopped immediately
• Ignoring feature support gaps

5. You are designing a migration plan using the Strangler fig pattern for a large monolithic app with features X, Y, and Z. Feature X is critical and must have zero downtime. How should you apply the pattern to ensure smooth migration?

hard

A. Replace feature X first with a new microservice and route only X requests there, keep Y and Z on legacy

B. Replace all features at once to avoid partial routing complexity

C. Stop the legacy app and start new microservices for all features simultaneously

D. Keep all features on legacy until new system is fully ready, then switch all at once

Solution

1. Step 1: Prioritize critical feature migration

   Feature X requires zero downtime, so migrate it first carefully.

2. Step 2: Apply gradual routing for feature X only

   Route requests for X to new microservice while Y and Z remain on legacy to reduce risk.

3. Step 3: Avoid full switch or stopping legacy abruptly

   The other options risk downtime or complexity by switching all features at once.

4. Final Answer:

   Replace feature X first with a new microservice and route only X requests there, keep Y and Z on legacy -> Option A

5. Quick Check:

   Gradual critical feature migration = D [OK]

Hint: Migrate critical features first, route requests gradually [OK]

Common Mistakes:

• Trying to replace all features at once
• Stopping legacy before new system ready
• Delaying critical feature migration