About Synchronous Request
Endpoints
The synchronous request-response pattern is a fundamental communication model used in various scenarios where a consumer requires an immediate response within the confines of agreed response times and in this type of interaction the consumer blocks and waits for a response on the same thread of execution.
The pattern enforces a literal and also a temporal coupling of the sender and receiver through the use of timeouts and connections. If the receiving system is offline, or cannot process the request in a timely manner or at all, the call will fail and could degrade performance of the caller if appropriate error handling is not provisioned or accounted for.
About Publish / Subscribe
Endpoints
The Publish / Subscribe pattern, enables an application to publish messages to multiple interested or subscribed consumers asynchronously allowing loose coupling of the senders to the receivers.
Also called: Pub/sub messaging - message oriented middleware.
From an Integration Platform and also from the Azure technology perspective Publish and Subscribe primarily applies to Azure Service Bus
About Asynchronous Processes, Events and Notifications
Once an Asynchronous process or communication or request is initiated, the Consumer does not wait and does not expect an immediate response or timely completion of a process. Rather the Consumer having initiated the request then continues its own execution or processing. For situations where the consumer needs a response, then the Producer will signal to the Consumer that a response is ready or the process has reached completion.
Such Asynchronous processes or requests are referred to as a non-blocking request as the execution thread of the client is not blocked. This allows systems to scale as more work can be done in a given amount of time.