Event types (domain, integration, notification) in Microservices - Architecture Diagram

System Overview - Event types (domain, integration, notification)

This system demonstrates three key event types used in microservices: domain events, integration events, and notification events. Domain events capture changes within a service's own data. Integration events enable communication between different services. Notification events inform users or external systems about important updates.

Architecture Diagram

User
  |
  v
Notification Service
  |
  v
Event Broker (Message Queue)
  /      |         \
 /       |          \
Service A  Service B  Service C
  |          |          |
  v          v          v
Domain DB  Integration DB  Notification DB

Components

User

external_user

Receives notifications about system events

Notification Service

service

Sends notification events to users or external systems

Event Broker (Message Queue)

message_queue

Routes events between services asynchronously

Service A

service

Generates domain events and consumes integration events

Service B

service

Consumes integration events and may generate new domain events

Service C

service

Consumes integration events and triggers notification events

Domain DB

database

Stores data for Service A including domain event state

Integration DB

database

Stores data for Service B related to integration events

Notification DB

database

Stores notification event history and user preferences

Request Flow - 6 Hops

Service A → Event Broker (Message Queue)

Event Broker (Message Queue) → Service B

Service B → Event Broker (Message Queue)

Event Broker (Message Queue) → Service C

Service C → Notification Service

Notification Service → User

Failure Scenario

Component Fails:Event Broker (Message Queue)

Impact:Events cannot be routed between services, causing delays or loss of domain, integration, and notification events

Mitigation:Use a highly available message queue cluster with replication and failover to maintain event flow

Architecture Quiz - 3 Questions

Which event type is generated within a service to represent internal state changes?

A Integration event

B Domain event

C Notification event

D API event

Design Principle

This architecture shows how different event types enable clear separation of concerns: domain events handle internal changes, integration events enable service communication, and notification events inform users. Using an event broker decouples services and supports asynchronous, scalable communication.

Practice

1. Which type of event in microservices captures important business actions inside a single service?

easy

A. Domain event

B. Integration event

C. Notification event

D. System event

Solution

1. Step 1: Understand event types in microservices

   Domain events represent significant business actions occurring within a single service boundary.

2. Step 2: Differentiate from other event types

   Integration events share data between services, and notification events alert users or external systems, so they are not internal business actions.

3. Final Answer:

   Domain event -> Option A

4. Quick Check:

   Business action inside service = Domain event [OK]

Hint: Domain events are about internal business actions [OK]

Common Mistakes:

• Confusing integration events with domain events
• Thinking notification events capture business logic
• Assuming system event is a standard event type

2. Which of the following is the correct way to describe an integration event in microservices?

easy

A. An event that triggers UI updates within the same service

B. An event that shares information between different services

C. An event that sends alerts to users only

D. An event that logs errors internally

Solution

1. Step 1: Define integration events

   Integration events are designed to share information or changes between different microservices to keep them in sync.

2. Step 2: Eliminate incorrect options

   UI updates are usually local, alerts to users are notification events, and error logs are internal diagnostics, not integration events.

3. Final Answer:

   An event that shares information between different services -> Option B

4. Quick Check:

   Sharing info between services = Integration event [OK]

Hint: Integration events connect multiple services [OK]

Common Mistakes:

• Mixing notification events with integration events
• Thinking integration events only affect one service
• Confusing error logs with integration events

3. Consider this code snippet in a microservice:

publishEvent({ type: 'UserRegistered', payload: { userId: 123 } });

What type of event is this most likely representing?

medium

A. Notification event

B. System event

C. Integration event

D. Domain event

Solution

1. Step 1: Analyze the event name and context

   The event 'UserRegistered' indicates a business action inside the service, such as a user signing up.

2. Step 2: Match event type to definition

   Since it captures a business action inside the service, it is a domain event, not a notification or integration event.

3. Final Answer:

   Domain event -> Option D

4. Quick Check:

   Business action event = Domain event [OK]

Hint: Event names with business actions are domain events [OK]

Common Mistakes:

• Assuming all events are integration events
• Confusing notification events with domain events
• Ignoring event naming conventions

4. A microservice is sending an event to notify users about a password change. The event is mistakenly labeled as an integration event. What is the main issue here?

medium

A. Notification events should not be sent to users

B. Password change is a domain event, not a notification

C. Notification events should not be labeled as integration events

D. Integration events cannot carry user-related data

Solution

1. Step 1: Identify the event purpose

   The event is meant to notify users, which fits the notification event type.

2. Step 2: Understand event labeling importance

   Labeling a notification event as an integration event causes confusion and wrong handling in the system.

3. Final Answer:

   Notification events should not be labeled as integration events -> Option C

4. Quick Check:

   Correct event labeling avoids confusion [OK]

Hint: Match event label to its purpose carefully [OK]

Common Mistakes:

• Mixing notification and integration event roles
• Assuming integration events can't have user data
• Thinking notification events are internal only

5. You are designing a microservices system where a user registration triggers multiple actions: updating internal user stats, notifying other services, and sending a welcome email. Which event types should you use for these actions respectively?

hard

A. Domain event, integration event, notification event

B. Integration event, domain event, notification event

C. Notification event, domain event, integration event

D. Domain event, notification event, integration event

Solution

1. Step 1: Map actions to event types

   Updating internal user stats is a business action inside the service, so it is a domain event.

2. Step 2: Identify cross-service communication

   Notifying other services requires sharing information between services, so it is an integration event.

3. Step 3: Recognize user alerts

   Sending a welcome email is a message to the user, which fits notification events.

4. Final Answer:

   Domain event, integration event, notification event -> Option A

5. Quick Check:

   Internal action, cross-service, user alert = Domain, Integration, Notification [OK]

Hint: Match event type to action scope: internal, cross-service, user [OK]

Common Mistakes:

• Swapping integration and notification events
• Using domain events for cross-service communication
• Confusing notification with domain events