Go(lang): about MaxIdleConnsPerHost in the http client's transport

Question

In case MaxIdleConnsPerHost is set to a high number, let's say 1000, the number of connections open will still depend on the other host, right? I mean, allowing 1000 idle connections with the same host will result in 1000 connections open as long as these are not closed by the other host?

So, effectively setting this value to a high number, will result in never closing a connection, but waiting for the other host to do it? am I interpreting this correctly?

Answer 1

Your understanding is correct. MaxIdleConnsPerHost restricts how many connections there are which are not actively serving requests, but which the client has not closed.

Idle connections are useful for web browsers because they can keep reusing connections for subsequent HTTP requests to the same server. Idle connections have a cost for the server, though. They use kernel resources, and you may run up against per process limits or kernel limits on the number of open connections, files, or handles, which may cause unexpected errors in your program, or even for other programs on the same machine.

As such, be careful when increasing MaxIdleConnsPerHost to a large number. It only makes sense to increase idle connections if you are seeing many connections in a short period from the same clients.