ERROR: Registering runner… failed runner=38BUk9-k status=404 Not Found

Question

I'm trying to register a gitlab runner on a new installation of gitlab (based on the omnibus rpm for centos7) but registration fails like this:

[root@ec2-x.y.z.w ~]# 
[root@ec2-x.y.z.w ~]# sudo gitlab-ci-multi-runner register
Running in system-mode.

Please enter the gitlab-ci coordinator URL (e.g. https://gitlab.com/):
http://ec2-x-y-z-w.compute-1.amazonaws.com/ 
Please enter the gitlab-ci token for this runner:
38BUk9-kgZkmmPHz-hsb
Please enter the gitlab-ci description for this runner:
[ec2-x-y-z-w.compute-1.amazonaws.com]: dcos runner 1
Please enter the gitlab-ci tags for this runner (comma separated):
dcos
Whether to run untagged builds [true/false]:
[false]: 
ERROR: Registering runner... failed runner=38BUk9-k status=404 Not         Found
PANIC: Failed to register this runner. Perhaps you are having network     problems 
[root@ec2-x-y-z-w ~]#

Answer 1

You seem to be running Gitlab Runner v9.x. This error occurs when you match a V9 runner with a Gitlab below V9. They are incompatible.

Gitlab Runner v9 started using the V4 API, but that is only available with Gitlab V9. Downgrade to 1.11.1, should work again.

In particular, if you are starting your Runner using the official docker image, don't use :latest tag, switch to