This document summarizes event sourcing, eventual consistency, CQRS, and using events in microservices. It discusses event sourcing pros like being a real world abstraction and enabling scalability, and cons like being eventually consistent and complex. It defines an event store as an immutable source of truth and explains how CQRS separates commands and queries. Microservices are recommended to encapsulate functionality and integrate with an event store. A demo of Apache Kafka is also mentioned.

1. Event Sourcing
ANTONÍN STOKLÁSEK
11. 2. 2018
PRESENTATION

2. Antonin Stoklasek
 Technical Team Leader
 Programmer 10+ years
 BSC Praha, pobočka Olomouc
 Java, Docker, React, …
 Twitter @tonda100
 GitHub tonda100

3. Agenda
 Event Sourcing
 Eventual consistency
 CQRS
 Events in micro-services
 Apache Kafka

4. Events matters
State is irrelevant

5. Event Sourcing
Pros
 Real world abstraction
 Feature encapsulation
 Scalability
 Performace
 Time traveling
Cons
 Eventualy consistent
 Complex
 Non-traditional
 Disk space usage

6. Eventual Consistency
 It was stored but not loaded (yet)
 It happens anyway
 Be ready
 Throughput
 Performance
 Stability

7. Event Store
 Source of truth
 Immutable
 Topics
 Publishing events
 Subscribing
 Events order guarantee
 Processing EXACTLY_ONCE vs. AT_LEAST_ONCE

8. CQRS
command
 Write operations
 Publishing events
query
 Read Models
 Subscribe to events
Command Query Responsibility Segregation

9. CQRS

10. Micro Services
 Encapsulation
 Remove unnecery dependencies
 Event store integration
 Performance and Scalability

11. Demo
Apache Kafka

12. Summary
 Eventual consistency is not that bad
 Ready by design
 Embrace micro services
 Do NOT mix read and write
 Greg Young and Sebastian Daschner

13. THANK YOU
@tonda100