Gitlab-CI runner: ignore self-signed certificate

gitlab-ci-multi-runner register

gave me

couldn't execute POST against https://xxxx/ci/api/v1/runners/register.json:
Post https://xxxx/ci/api/v1/runners/register.json: 
x509: cannot validate certificate for xxxx because it doesn't contain any IP SANs

Is there a way to disable certification validation?

I'm using Gitlab 8.13.1 and gitlab-ci-multi-runner 1.11.2.

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

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.

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 root@192.168.1.2:/etc/gitlab-runner/certs

Thanks @Moon Light @Wassim Dhif

The following steps worked in my environment. (Ubuntu)

Download certificate
I did not have access to the gitlab server. Therefore,

1. Open https://some-host-gitlab.com in browser (I use chrome).
2. View site information, usually a green lock in URL bar.
3. Download/Export certificate by navigating to certificate information(chrome, firefox has this option)

In gitlab-runner host

1. Rename the downloaded certificate with .crt

   $ mv some-host-gitlab.com some-host-gitlab.com.crt

2. Register the runner now with this file

$ sudo gitlab-runner register --tls-ca-file /path/to/some-host-gitlab.com.crt

I was able to register runner to a project.

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 setup the following the following worked as well. It's just important that IP/Name used for creating certificate matches IP/Name used for registering the runner.

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

Furthermore, it could be necessary to add a line for hostname lookup to the runners config.toml file also (section [runners.docker]):
extra_hosts = ["git.domain.com:192.168.99.100"]
see also https://gitlab.com/gitlab-org/gitlab-runner/issues/2209

In addition, there could be some network-trouble if for gitlab/gitlab-runner network-mode host is used, it has to be added to the config.toml as well, as it starts additional containers, which otherwise could have a problem to connect to the gitlab-host ((section [runners.docker]):
network_mode="host"

Finally, there might be an issue with the self-signed SSL-Cert (https://gitlab.com/gitlab-org/gitlab-runner/issues/2659).
A dirty workaround is to add
environment = ["GIT_SSL_NO_VERIFY=true"]
to the [[runners]] section.