Event sourcing pattern in Microservices - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the Event Sourcing pattern?

Event Sourcing is a design pattern where all changes to application state are stored as a sequence of events. Instead of saving just the current state, the system saves every change as an event, allowing the state to be rebuilt by replaying these events.

intermediate

How does Event Sourcing help with data consistency in microservices?

By storing all changes as events, Event Sourcing ensures a clear, immutable history of state changes. This helps microservices maintain consistency by replaying events to reach the current state, avoiding conflicts from concurrent updates.

beginner

What is an event store in Event Sourcing?

An event store is a specialized database that saves all events in order. It acts like a journal, recording every change. The event store allows replaying events to rebuild the current state or audit past changes.

advanced

What is a common challenge when using Event Sourcing?

One challenge is handling event versioning when the event structure changes over time. Systems must support backward compatibility or migration strategies to replay old events correctly.

intermediate

How does Event Sourcing relate to CQRS (Command Query Responsibility Segregation)?

Event Sourcing often pairs with CQRS, where commands change state by generating events, and queries read from a separate, optimized read model built from those events. This separation improves scalability and performance.

What does Event Sourcing store in its database?

A A sequence of events representing all state changes

B Only the current state snapshot

C User session data

D Database schema changes

Event Sourcing stores every change as an event, not just the current state.

Which component is responsible for saving events in Event Sourcing?

A Load balancer

B Event store

C Cache

D API gateway

The event store is the database that saves all events in order.

Why is Event Sourcing useful for auditing?

A Because it keeps a full history of all changes

B Because it deletes old data

C Because it encrypts data

D Because it caches queries

Event Sourcing records every change, making it easy to audit the full history.

What is a key benefit of combining Event Sourcing with CQRS?

A Simplifying database schema

B Encrypting all events

C Reducing network latency

D Separating write and read models for better scalability

CQRS separates commands and queries, improving scalability when used with Event Sourcing.

What is a common difficulty when evolving an Event Sourcing system?

A Encrypting the event store

B Scaling the user interface

C Handling changes in event formats over time

D Managing user sessions

Event versioning is challenging because old events must still be replayed correctly after changes.

Explain how Event Sourcing works and why it is useful in microservices.

Think about saving every change instead of just the final state.

Describe the relationship between Event Sourcing and CQRS and how they improve system design.

Consider how commands and queries are handled differently.