In modern app development, when clients need to interact with remote APIs for business logic or services, the Asynchronous Request-Reply pattern shines. Here's how it works :

• Client Makes Request: The client (like a web browser) sends a request to the backend API over HTTP(S).

• Backend Acknowledges: Upon receiving the request, the backend immediately acknowledges it, letting the client know it's been received.

• Backend Processes Asynchronously: Instead of making the client wait, the backend processes the request asynchronously. This means it can handle multiple tasks simultaneously without blocking.

• Immediate Response: While the backend works, the client gets an immediate response, indicating the request has been accepted.

• Notification of Completion: Once processing is complete, the backend notifies the client, providing the result or status update.
  Benefits:

• Improved Responsiveness: Clients get immediate feedback, making interactions smoother.

• Efficient Resource Utilization: Asynchronous processing allows the backend to handle tasks concurrently, optimizing resource usage.

• Scalability: The system can handle more requests without sacrificing performance.

This approach simplifies communication between clients and servers, making applications more responsive and scalable.

✅ When to Use This Pattern:

• Client-Side Code: Ideal for client-side applications like browsers where setting up callback endpoints or long-running connections is complex.

• Service Calls Over HTTP: Useful when only HTTP protocol is available and firewall restrictions prevent callback firing on the client-side.

• Integration with Legacy Architectures: When integrating with older systems that lack support for modern callback technologies such as WebSockets or webhooks.

❌ When Not to Use This Pattern:

• Alternative Services Available: If there's a service designed for asynchronous notifications like Azure Event Grid, it may be a better fit.

• Real-Time Streaming Required: Not suitable when real-time streaming responses are needed.

• Many Results with Low Latency: For scenarios where the client needs to collect numerous results with low latency, consider a service bus pattern instead.

• Persistent Network Connections Supported: If server-side persistent network connections like WebSockets or SignalR are feasible, they can be used for real-time result notifications.

• Network Design Constraints: If network design allows for opening ports to receive asynchronous callbacks or webhooks, consider those options.

• Using the Asynchronous Request-Reply pattern can simplify communication in certain scenarios, but it's essential to consider alternative solutions when they better align with specific requirements or constraints.

More Details :

1- https://learn.microsoft.com/en-us/azure/architecture/patterns/async-request-reply?WT.mc_id=DX-MVP-5004571

2- https://youtu.be/LCbR58sCmvQ?si=qrSA_2zlzG0cV9_i