Independent ownership requires controlling writes and schema evolution. A shared database can silently couple services even when HTTP interfaces look separate.
Before you start
You should understand HTTP, database transactions and the difference between one process and independently failing services. Draw the participants and message direction before choosing a pattern. Include timeout, duplicate delivery and recovery in the model instead of considering only successful requests.
The practical goal is to reason through this situation: The billing service owns invoice updates and publishes a supported interface. Read the walkthrough first, then try the interview exercise before opening its answer. The important part is explaining the decision and its consequences, rather than remembering a definition alone.
Step-by-step walkthrough
Step 1: Name the authoritative owner
Assign invoice rules and writes to billing.
Step 2: Expose supported access
Use an API or replicated read model for other services.
Step 3: Define freshness and evolution
Document lag and version compatibility rather than sharing unrestricted SQL access.
Worked scenario
The billing service owns invoice updates and publishes a supported interface.
An order service directly updates billing’s invoice table to mark a refund. It bypasses billing validation and becomes coupled to billing’s schema release. A supported refund operation preserves ownership; a replicated dashboard view serves reads without pretending to be an authorized write path.
Common mistake
Directly editing another service’s tables bypasses its validation and release contract.
Verify the behavior
Change the owner’s schema and verify consumers continue through the supported contract.
Interview exercise
Read another service’s data.
Answer and reasoning
Use an API or replicated read model with defined freshness, rather than unrestricted cross-service writes.
Continue learning
Compare the scenario with the Microservices interview questions and test your understanding with the Microservices MCQs. For terminology and implementation details, consult the reference material.