Strangler fig pattern in Microservices - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

Understanding the core idea of the Strangler Fig Pattern

Which of the following best describes the main goal of the Strangler Fig Pattern in system design?

A To replace a legacy system gradually by building new features as separate components that eventually take over all functionality.

B To immediately rewrite the entire legacy system from scratch to improve performance and scalability.

C To run the legacy system and new system in parallel indefinitely without integration.

D To create a monolithic application that handles all legacy and new features in one codebase.

💡 Hint

Think about how the pattern helps in transitioning from old to new without big risks.

The Strangler Fig Pattern focuses on gradually replacing parts of a legacy system by building new components that take over functionality step-by-step, reducing risk and downtime.

❓ Architecture

intermediate

Identifying components in a Strangler Fig architecture

In a Strangler Fig Pattern implementation, which component acts as the traffic director that routes requests between the legacy system and new microservices?

A Message Queue

B Load Balancer

C API Gateway

D Database

💡 Hint

Consider which component controls request routing and can decide where to send each request.

The API Gateway acts as the traffic director by routing requests either to the legacy system or to new microservices during the gradual migration.

❓ scaling

advanced

Scaling challenges during Strangler Fig migration

What is a common scaling challenge when running both legacy and new systems simultaneously in a Strangler Fig migration?

A Reducing the number of microservices to avoid complexity.

B Ensuring consistent data synchronization between legacy and new components.

C Eliminating all legacy system dependencies immediately.

D Deploying the new system on the same hardware as the legacy system.

💡 Hint

Think about data consistency when two systems handle parts of the workload.

During migration, both systems may need to share or synchronize data, which can be complex and affect scaling.

❓ tradeoff

advanced

Tradeoffs in choosing Strangler Fig Pattern

Which tradeoff is most associated with using the Strangler Fig Pattern for system migration?

A No need for testing since old system remains untouched.

B Faster migration but higher risk of breaking existing features.

C Complete system rewrite with no backward compatibility.

D Longer migration time but reduced risk of system downtime.

💡 Hint

Consider the balance between speed and safety in migration strategies.

The Strangler Fig Pattern trades longer migration time for safer, incremental replacement, minimizing downtime and risk.

❓ estimation

expert

Estimating capacity needs during Strangler Fig migration

You are migrating a legacy monolith to microservices using the Strangler Fig Pattern. The legacy system handles 10,000 requests per second. You plan to migrate 30% of functionality to new microservices initially. What is the minimum expected request load on the new microservices after migration starts?

A 3,000 requests per second

B 7,000 requests per second

C 10,000 requests per second

D 30,000 requests per second

💡 Hint

Calculate the portion of total requests handled by new microservices based on migrated functionality percentage.

If 30% of functionality is migrated, the new microservices will handle approximately 30% of the total 10,000 requests, which is 3,000 requests per second.

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