<strong>Message queues</strong> are systems that enable asynchronous communication between services by storing messages until they can be processed. They decouple services, improve reliability, and handle traffic spikes.
The Post Office Analogy
You don't hand letters directly to recipients. You drop them at the post office (queue), which holds them until the recipient picks them up. Services work the same way.
Sender (Producer)
Sends mail
Post Office (Queue)
Holds mail
Receiver (Consumer)
Picks up mail
Sends Message
Stores Messages
Processes Message
Producer sends message
Service A sends 'process-order' message
Queue stores message
RabbitMQ/SQS holds message until processed
Consumer pulls message
Service B fetches message when ready
Process and acknowledge
Service B processes order, sends ACK
Message deleted
Queue removes message after ACK
Wrong
"Message queues are just for big systems"
Correct
<strong>Queues benefit any async workflow</strong>: email sending, image processing, notifications. They prevent blocking, handle failures, and enable scaling.
E-commerce order processing:
User places order → message sent to queue
Payment service processes payment (async)
Inventory service updates stock (async)
Email service sends confirmation (async)
If one service is down, messages wait in queue