Nginx/gitlab-ci-error.log overflowing with Host not found

My nginx/gitlab-ci-error.log is overflowing with messages like this:

2016/06/21 12:48:49 [error] 11431#0: *626 myhost.mydomain.com could not be resolved (3: Host not found), client: 127.0.0.1, server: gitlab-ci.mydomain.com, request: "POST /api/v1/builds/register.json HTTP/1.1", host: "gitlab-ci.mydomain.com"

In /etc/hosts I have defined myhost.mydomain.com and gitlab-ci.mydomain.com to both point to 127.0.0.1.

This problem is so persistent, the drive for my logs is at risk of running out of space. Since all the hostnames resolve, I have no idea what the problem is. I have tried hunting down every possible reference to “myhost.homain.com” and change it to different values (then gitlab-ctl restart), but nothing seems to have any effect. I keep getting the same error message over and over.

Any ideas what causes this or how to troubleshoot further?

Tom