Messaging

Every messaging platform (Kafka, RabbitMQ, ActiveMQ, etc.) uses the same fundamental components.

Core messaging architecture:

Producer → Broker → Consumer

The message is the data flowing through the system.

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Message

A message is a piece of information sent from one system to another through a messaging platform.

It usually represents an event or business data that needs to be processed.

Example:

{
  "eventType": "OrderCreated",
  "orderId": "ORD123",
  "amount": 500
}

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Why Messages Exist

Messages allow systems to communicate asynchronously and loosely coupled.

Instead of direct service calls:

Order Service → HTTP → Payment Service

We send a message:

Order Service → Message → Broker → Payment Service

Benefits:

• services don’t depend on each other availability
• better scalability
• asynchronous processing
• improved reliability

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Message Structure (Best Practice)

Good event messages normally contain:

Field	Purpose
eventType	What happened
eventId	Unique ID
timestamp	When event happened
payload	Business data

Example:

{
  "eventId": "12345",
  "eventType": "CustomerCreated",
  "timestamp": "2026-03-14T10:10:00Z",
  "payload": {
    "customerId": "C001",
    "name": "John"
  }
}

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Where Messages Are Used

Banking systems

CustomerCreated
AccountCreated
MoneyTransferred
TransactionCompleted

E‑commerce systems

OrderCreated
PaymentCompleted
OrderShipped

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Message Design Best Practices

1. Use meaningful event names

Good:

order.created
payment.completed
customer.registered

Avoid:

event1
data1

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2. Include event version

Example:

customer.created.v1

This prevents breaking changes when event structure evolves.

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3. Keep messages small

Messaging systems are designed for event metadata, not large payloads.

Bad example:

Sending entire PDF document

Better:

Send documentId Store document in external storage.

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Where Messages Are Stored (Kafka Preview)

Kafka stores messages as log files on disk.

• based on log.dirs in server.properties file under config.

Example directory:

/var/lib/kafka/data

Each partition is stored as an append‑only log.

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