Lesson 2: Event-Driven Architecture#

Synchronous vs. Asynchronous#

• Synchronous (Request/Response): Client waits for the server to respond (e.g., HTTP REST).
• Asynchronous (Event-Driven): Client sends a message and continues work. The receiver processes it later.

Core Concepts#

Message Queues (Point-to-Point)#

A message is sent to a queue and processed by exactly one consumer.

• Use Case: Background jobs (e.g., image resizing).

Pub/Sub (Publish/Subscribe)#

A message (event) is published to a topic. Multiple subscribers can receive a copy.

• Use Case: notifying multiple services (e.g., “UserSignedUp” -> EmailService, AnalyticsService).

🛠️ Sruja Perspective: Modeling Events#

Sruja supports queue as a first-class citizen to model asynchronous communication.

architecture "Notification System" {
    system Notifications "Notification System" {
        container AuthService "Auth Service" {
            technology "Node.js"
        }

        // Define a queue or topic
        queue UserEvents "User Events Topic" {
            technology "Kafka"
            description "Events related to user lifecycle (signup, login)."
        }

        container EmailService "Email Service" {
            technology "Python"
        }

        container AnalyticsService "Analytics Service" {
            technology "Spark"
        }

        // Pub/Sub flow
        AuthService -> UserEvents "Publishes 'UserSignedUp'"
        UserEvents -> EmailService "Consumes"
        UserEvents -> AnalyticsService "Consumes"
    }
}