maximum reasonable timeout for a synchronous HTTP request

Question

This applies to non-user facing backend applications communicating with each other through HTTP. I'm wondering if there is a guideline for a maximum timeout for a synchronous HTTP request. For example, let's say a request can take up to 10 minutes to complete. Can I simply create a worker thread on the client and, in the worker thread, invoke the request synchronously? Or should I implement the request asynchronously, to return HTTP 202 Accepted and spin off a worker thread on the server side to complete the request and figure out a way to send the results back, presumable through a messaging framework? One of my concerns is it safe to keep an socket open for an extended period of time?

Solution

How long a socket connection can remain open (without activity) depends on the (quality of the) network infrastructure.

A client HTTP request waiting for an answer from a server results in an open socket connection without any data going through that connection for a while. A proxy server might decide to close such inactive connections after 5 minutes. Similarly, a firewall can decide to close connections that are open for more than 30 minutes, active or not.

But since you are in the backend, these cases can be tested (just let the server thread handling the request sleep for a certain time before giving an answer). Once it is verified that socket connections are not closed by different network components, it is safe to rely on socket connections to remain open. Keep in mind though that network cables can be unplugged and servers can crash - you will always need a strategy to handle disruptions.

As for synchronous and asynchronous: both are feasable and both have advantages and disadvantages. But what is right for you depends on a whole lot more than just the reliability of socket connections.