Gitlab-CI runner: ignore self-signed certificate

Based on Wassim's answer, and gitlab documentation about tls-self-signed and custom CA-signed certificates, here's to save some time if you're not the admin of the gitlab server but just of the server with the runners (and if the runner is run as root):

SERVER=gitlab.example.com
PORT=443
CERTIFICATE=/etc/gitlab-runner/certs/${SERVER}.crt

# Create the certificates hierarchy expected by gitlab
sudo mkdir -p $(dirname "$CERTIFICATE")

# Get the certificate in PEM format and store it
openssl s_client -connect ${SERVER}:${PORT} -showcerts </dev/null 2>/dev/null | sed -e '/-----BEGIN/,/-----END/!d' | sudo tee "$CERTIFICATE" >/dev/null

# Register your runner
gitlab-runner register --tls-ca-file="$CERTIFICATE" [your other options]

Update 1: CERTIFICATE must be an absolute path to the certificate file.

Update 2: it might still fail with custom CA-signed because of gitlab-runner bug #2675

Ok I followed step by step this post http://moonlightbox.logdown.com/posts/2016/09/12/gitlab-ci-runner-register-x509-error and then it worked like a charm. To prevent dead link I copy the steps below:

First edit ssl configuration on the GitLab server (not the runner)

vim /etc/pki/tls/openssl.cnf

[ v3_ca ]
subjectAltName=IP:192.168.1.1 <---- Add this line. 192.168.1.1 is your GitLab server IP.

Re-generate self-signed certificate

cd /etc/gitlab/ssl
sudo openssl req -x509 -nodes -days 3650 -newkey rsa:2048 -keyout /etc/gitlab/ssl/192.168.1.1.key -out /etc/gitlab/ssl/192.168.1.1.crt
sudo openssl dhparam -out /etc/gitlab/ssl/dhparam.pem 2048
sudo gitlab-ctl restart

Copy the new CA to the GitLab CI runner

scp /etc/gitlab/ssl/192.168.1.1.crt [email protected]:/etc/gitlab-runner/certs

Thanks @Moon Light @Wassim Dhif

Currently there is no possibility to run the multi runner with an insecure ssl option.

There is currently an open issue at GitLab about that.

Still you should be able to get your certificate, make it a PEM file and give it to the runner command using --tls-ca-file

To craft the PEM file use openssl.
openssl x509 -in mycert.crt -out mycert.pem -outform PEM

In my case I got it working by adding the path to the .pem file as following:

sudo gitlab-runner register --tls-ca-file /my/path/gitlab/gitlab.myserver.com.pem

Often, gitlab-runners are hosted in a docker container. In that case, one needs to make sure that the tls-ca-file is available in the container.