IBM IHS error: mod_domino: apr_socket_connect, could not connect to Domino Server

I just had a problem getting IHS to communicate with Domino 9.0.1. The IHS error.log stated the following:

mod_domino: apr_socket_connect, could not connect to Domino Server

I browsed the documentation and found:

The Domino HTTP server only accepts connections that originate from the same computer. By default, mod_domino uses the local loop back address of 127.0.0.1 to connect to the Domino HTTP server. Both server processes must run on the same computer.

When IHS is installed as a part of Domino the Domino HTTP task listens to port 9288. I figured I needed to find out which IP addresses the HTTP task was listening on port 9288 on. Netstat is good at this and revealed the following:

TCP    10.201.17.12:9288      0.0.0.0:0             LISTENING

Domino was listening on port 9288, but not on the loopback address.

Suddenly it struck me that I had to add localhost to field in the server document where you specify the host name(s) Domino HTTP task listens to.

I added localhost, restarted the Domino server and voila!