HttpWebRequest Port Exhaustion

Question

We are using a Windows Service to make very frequent HTTP calls to an internal REST service (20-40 calls per second), but notice a long delay in getting responses after the service runs for several minutes.

Looking at netstat, there are quite a few ports with "TIME_WAIT" status, and it seems we may be running out of ports.

How can we ensure that ports are reused?

Answer 1

There is a limit in the number of simultaneous outgoing HTTP connections. You can control this by using the System.Net.ServicePointManager.DefaultConnectionLimit static property before creating the HttpWebRequest objects

It might be worthwhile setting this to a higher value than the default which I believe is 2.

If this does not help then you can also increase the default ThreadPool size to allow you to create more requests quicker. The thread pool only ramps up its number of threads gradually - a new thread per every half second, IIRC

Answer 2

How can we ensure that ports are reused? Not set the connection limit to a value that almost guarantees that they won't be.

It looks like someone has monkeyed with the ServicePointManager at some point. I'd limit the ServicePoint for this origin: to encourage http pipelining and connection reuse:

ServicePointManager.FindServicePoint(Uri).ConnectionLimit = someSensibleValue;