Database Strategy for Microservices with Minimal Code Changes

A company is migrating a monolithic legacy application to a microservices architecture on AWS. The application currently uses a relational database with complex joins. The migration must minimize application changes. Which database strategy should be used for the new architecture?

Quick Answer

The answer is to use a single Amazon RDS instance shared by all microservices. This is correct because the requirement to minimize application changes means the microservices must continue using the existing relational database with complex joins, preserving all current SQL queries and join logic without needing to decompose data or implement API-based access patterns, which would demand significant rewrites. On the AWS Certified Solutions Architect Professional SAP-C02 exam, this scenario tests your ability to balance architectural purity against practical migration constraints—a common trap is assuming microservices always require separate databases, but the question explicitly prioritizes minimal changes over ideal decoupling. Remember the memory tip: “When joins must stay, share the RDS all the way.”

⚠ Common exam trap

Many candidates assume microservices require separate databases per service (database-per-service pattern) without considering the constraint of minimizing application changes, leading them to incorrectly choose option A.

Answer choices

Why each option matters

Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.

Correct answer & explanation

✓

Use a single Amazon RDS instance shared by all microservices.

The requirement to minimize application changes means the microservices must continue to use the same relational database with complex joins. A single shared Amazon RDS instance preserves the existing SQL queries and join logic without requiring data decomposition or API-based data access patterns, which would necessitate significant application rewrites.

Answer analysis

Option-by-option breakdown

For each option: why learners choose it and why it is or isn't the right answer here.

✗
Use a separate Amazon RDS instance for each microservice.
Why it's wrong here
Requires significant code changes to handle joins across databases.
✓
Use a single Amazon RDS instance shared by all microservices.
Why this is correct
Minimizes application changes by preserving the existing relational database schema and joins.
✗
Use Amazon Aurora with RDS Proxy in front of it.
Why it's wrong here
Does not address the need for complex joins across microservices.
✗
Use Amazon DynamoDB as a shared database for all microservices.
Why it's wrong here
NoSQL does not support complex joins and would require major refactoring.

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Same concept, more angles

1 more way this is tested on SAP-C02

These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.

Variation 1. A company is migrating a legacy monolithic application to a microservices architecture on AWS. The application has a relational database with complex queries. The team wants to minimize changes to the existing codebase. Which database migration strategy should be recommended?

hard

✓ A.Use Amazon RDS for MySQL or PostgreSQL with read replicas.
B.Use Amazon Aurora Serverless to reduce management.
C.Store data in Amazon S3 and use Athena for queries.
D.Migrate to Amazon DynamoDB for scalability.

Why A: Using Amazon RDS with the same database engine (MySQL or PostgreSQL) minimizes code changes, as the application can connect via standard SQL drivers. Read replicas can help with read scaling without altering the codebase. Option B is wrong because Aurora Serverless may require configuration changes and does not necessarily minimize code changes. Option C is wrong because S3 and Athena are not suitable for transactional relational queries and would require significant architectural changes. Option D is wrong because DynamoDB would require schema redesign and application changes to use NoSQL.

Last reviewed: Jun 11, 2026

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