Any of these factors can add latency to the response. Some can be mitigated by scaling out the backend. Others, such as network infrastructure, are largely out of the control of the application developer. Most APIs can respond quickly enough for responses to arrive back over the same connection. Application code can make a synchronous API call in a non-blocking way, giving the appearance of asynchronous processing, which is recommended for I/O-bound operations.
https://learn.microsoft.com/en-us/azure/architecture/patterns/async-request-reply
