Message Driven

Asynchronous message-passing

“Reactive Systems rely on asynchronous message-passing to establish a boundary between components.” – Reactive Manifesto

When to use

Decoupling components.

Why it matters

  • Isolation: Components don’t call each other directly (blocking). They leave messages.
  • Load Management: Back-pressure. If A sends too fast, B can say “Stop” or buffer the messages.

Signs of Violation

  • Deeply nested synchronous function calls across service boundaries.
  • Tight coupling between sender and receiver.

Explanation

Problem

Direct calls couple time and space. Both sender and receiver must be there now.

Solution

Messages. “Packet of data sent to a specific destination”.

Real world analogy

Email vs Phone Call. Phone call requires both parties to be available (Coupled). Email (Message) allows the receiver to read it whenever they can.

Pros and Cons

Pros Cons
  • Decoupling
  • Non-blocking
    		•
  • Debugging async flows
    		•

    Comparison

    • Event Driven: Similar, but “Events” are broadcast (Listener decides), “Messages” are directed (Sender decides destination).

    Code example

    Typescript

    Bad (Violation - Direct)

    Good (Adherence)

    PHP

    Good (Adherence)