Question

What is the technical objective of using an event bus to facilitate communication between services rather than using synchronous REST API calls?

Accepted Answer

The technical objective of using an event bus is to decouple services by enabling asynchronous communication. Decoupling means that services do not need to know about each other&#x27;s existence, location, or current operational state to perform their functions. In a synchronous REST API call, the calling service must wait for the receiving service to process the request and send back a response, creating a tight dependency where both services must be active and functional at the same time. If the receiving service fails or slows down, the calling service is blocked or fails as well. An event bus acts as an intermediary message broker that receives events, which are notifications that something has happened, such as a user registering an account. The sender publishes an event to the bus and immediately continues its own work without waiting for any result. The event bus stores this event and delivers it to any number of interested services, known as subscribers, whenever they are ready to process it. This architecture increases system resilience because if a subscriber service is temporarily offline, the event remains safe in the bus and is processed once the service recovers. It also improves scalability, as you can add new services that listen to the same event stream without modifying the code of the original sending service.

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What is the technical objective of using an event bus to facilitate communication between services rather than using synchronous REST API calls?