What are message brokers generally used for? Why can't we go directly from service to service via REST?

Message brokers are needed for asynchronous and reliable data exchange between services. They provide:

• Buffering of messages, allowing services to operate independently in time.
• Delivery guarantees (e.g., retries in case of failures).
• Scalability and load balancing.
• Decoupling of services from each other, reducing coupling.

Direct service calls via REST have limitations:

• Rigid synchronous connection: if one service is unavailable, the call will fail.
• More difficult to scale and load balance.
• No built-in delivery guarantees or retries.

Therefore, message brokers enhance the resilience and flexibility of architecture, especially in distributed systems.