While I was implementing a few more changes on my web server - mostly adding the sorely needed blacklistd configuration for sshd - I noticed that NGINX’s log was showing occasional errors when trying to contact the Isso process. They all had one thing in common, namely that they were all trying to contact ISSO via IPV6 as the server has both stacks enabled. Turns out that isso only listens on an IPV4 socket and I could not find an obvious way to get it to listen on both.

The easy “fix” was to change the NGINX configuration to use proxy_pass http://127.0.0.1:12345 instead of proxy_pass http://localhost:12345. The other option would’ve been to set up the resolver configuration for this section of the NGINX configuration with IPV6 disabled. Given that we’re talking about localhost here, it didn’t make a lot of sense to me to have DNS lookup in the first place, so “hardcoding” the IP address for localhost made more sense to me.

I did have a quick look at the Isso source code and it doesn’t look like there is a way to tell the server to listen both on IPV4 and IPV6, at least not with the basic gevent server I’m using. It might be possible by switching to another uWSGI server but I’m trying to keep this setup as simple as possible. Suggestions are appreciated, though.