feat: event sourcing, eda

courses/itmo-software-design/README.md

@@ -1,4 +1,6 @@
 ## Lectures
 
 - [Domain Driven Design](./domain-driven-design.md)
-- [Event Driven Architecture](./event-driven-architecture.md)
+- [Event Driven Architecture](./event-driven-architecture.md)
+- [Consistent Hashing](./consistent-hashing.md)
+- [Load Balancing](./load-balancing.md)

courses/itmo-software-design/event-driven-architecture.md

@@ -1 +1,45 @@
-# todo
+## Event-driven architecture
+
+**Event sourcing** - is a pattern that uses an append-only event log to store the full history of actions taken on data
+in a domain.
+
+![](./docs/eda/event-sourcing.png)
+
+The application state is derived by replaying the events in the log.
+> This allows the state to be rebuilt at any point in time by replaying the events from the event log.
+
+Common example of event sourcing is a Git.
+
+**Event** - is a record of something that has happened in the domain.
+> Event is a subset of the message.
+>
+> - Event don't have a destination.
+> - Event is a named fact that something has happened.
+>
+> E.g: order created, order shipped, order cancelled.
+
+**Event log** - is a sequence of events that happened in the domain.
+
+**Event driven architecture** - is a pattern that uses events to trigger and communicate between decoupled services.
+> Usually implemented using a message broker, such as Kafka or RabbitMQ.
+
+- EDA is asynchronous, which means that the sender and receiver of the message don't need to interact
+  instantly, events can be processed at a later time.
+- We can have multiple consumers of the same event, each consumer can do something different with it. (pub/sub model)
+- Easy to add new services, low coupling between services.
+- High system reliability, because if one service is down, the event will be stored in the event log
+  and will be processed later.
+
+![](./docs/eda/eda.png)
+
+**CQRS** (Command Query Responsibility Segregation) - is a pattern that separates the read and write operations
+for a data store.
+
+> Different services can handle read and write operations separately.
+
+### Resources
+
+- https://aws.amazon.com/ru/event-driven-architecture/
+- https://www.linkedin.com/pulse/event-sourcing-pattern-distributed-designpatterns-pratik-pandey/
+- https://docs.axoniq.io/reference-guide/architecture-overview/event-sourcing
+- https://microservices.io/patterns/data/saga.html