register gitlab-runner

[Pre requisite]
1. edit /etc/hosts for adding gitlab server
 $ cat /etc/hosts
 127.0.0.1       localhost holyxlat.com

[add certificate file to /etc/gitlab-runner/certs]
$ mkdir /etc/gitlab-runner/certs
$ cp /etc/gitlab/ssl/holyxlat.com.crt /etc/gitlab-runner/certs/.   // sample for my case

[Register gitlab-runner]
$ sudo gitlab-runner register
Runtime platform                                    arch=amd64 os=linux pid=2305                                             2 revision=4745a6f3 version=11.8.0
Running in system-mode.

Please enter the gitlab-ci coordinator URL (e.g. https://gitlab.com/):
https://holyxlat.com/
Please enter the gitlab-ci token for this runner:
<My Token>
Please enter the gitlab-ci description for this runner:
[<my host>]: test-gitlab-ci
Please enter the gitlab-ci tags for this runner (comma separated):
test-gitlab-ci
Registering runner... succeeded                     runner=SvgtcSrN
Please enter the executor: ssh, docker-ssh+machine, kubernetes, docker, parallel                                             s, shell, virtualbox, docker+machine, docker-ssh:
docker
Please enter the default Docker image (e.g. ruby:2.1):
alpine:latest
Runner registered successfully. Feel free to start it, but if it's running already the config should be automatically reloaded!