Event replay in Microservices - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is event replay in microservices?

Event replay is the process of reprocessing past events from an event store to rebuild system state or recover from failures.

beginner

Why is event replay useful in microservices?

It helps to restore data consistency, recover lost state, and test new features by replaying historical events.

beginner

What component typically stores events for replay in a microservices architecture?

An event store or event log stores all events in order for later replay.

intermediate

What is a key challenge when implementing event replay?

Ensuring idempotency so that replaying events does not cause duplicate side effects or inconsistent state.

intermediate

How does event replay relate to CQRS (Command Query Responsibility Segregation)?

Event replay is often used to rebuild read models in CQRS by replaying events to update query databases.

What is the main purpose of event replay in microservices?

A To monitor service health

B To send new commands to services

C To rebuild system state from past events

D To delete old events from the event store

Event replay reprocesses past events to restore or rebuild system state.

Which component stores events for replay?

A Load balancer

B Event store

C Cache

D API gateway

The event store keeps all events in order for replay.

What problem does idempotency solve in event replay?

A Avoiding duplicate effects when replaying events

B Increasing event storage speed

C Encrypting event data

D Balancing load between services

Idempotency ensures replaying events multiple times does not cause repeated side effects.

Event replay is commonly used to rebuild which part of CQRS?

A Authentication service

B Command model

C API layer

D Read model

Replaying events updates the read model in CQRS.

When might event replay be triggered?

A After a system crash to recover state

B To send real-time notifications

C To scale services horizontally

D To encrypt data in transit

Event replay helps recover lost state after failures.

Explain what event replay is and why it is important in microservices.

Think about how past events help restore system state.

Describe the challenges of implementing event replay and how to address them.

Consider what happens if events are processed multiple times.