Message Patterns

There are different ways to structure message communication between systems.

Publish/Subscribe Pattern

Publishers send messages to a topic or channel without knowing who will receive them. Subscribers express interest in specific topics and receive all messages published to those topics.

Pub/Sub Nature:

• One-to-Many: A single message can be delivered to multiple subscribers.
• Decoupling: Publishers and subscribers don’t need to know about each other.
• Dynamic Subscription: Subscribers can join or leave at any time.
• Topic-Based: Messages are organized by topics or channels.

Pub/Sub Use cases:

• Real-time notifications across multiple services
• Event-driven architectures where multiple consumers need the same data
• Log aggregation and monitoring systems

Point-to-Point Pattern

Messages are sent directly from one sender to one specific receiver. Messages are typically placed in a queue where they are consumed by a single consumer.

P2P:

• One-to-One: Each message is consumed by exactly one receiver.
• Message Ordering: Messages are typically processed in the order they arrive.
• Load Distribution: Multiple consumers can read from the same queue for load balancing.
• Guaranteed Delivery: Messages remain in the queue until successfully processed.

P2P Use cases:

• Task distribution among worker nodes
• Request-response communication between services
• Sequential processing of transactions
• Background job processing

Request-Reply Pattern

A pattern where a sender sends a message and waits for a response from the receiver. The sender includes a reply-to address in the message so the receiver knows where to send the response. This pattern combines aspects of both synchronous and asynchronous communication, allowing for non-blocking request-response interactions.

Message Ordering

Message ordering guarantees vary by pattern and implementation:

• FIFO Ordering: Messages are processed in the order they are sent.
• Partition Ordering: Messages within the same partition maintain order.
• No Ordering: Messages may be processed in any order for maximum throughput.

Why you need to know this?

Basically there are 2 common scenarios you want to use such patterns.

1. You have multiple services that need to communicate with each other in a decoupled way. In this case you will use Publish/Subscribe pattern. Such pattern allow async communication and multiple services can listen to the same event. Ideally for event-driven architectures. For instance using Kafka topics or similar messaging systems.

2. You have a task that needs to be processed by a single service or worker. In this case you will use Point-to-Point pattern. Such pattern ensure that only one service will process the message. Ideal for task distribution and load balancing. For instance using AWS SQS or RabbitMQ.