...

There are some components need to be installed, you will need to run below command lines one by one.

sudo yum install -y install curl policycoreutils-python openssh-server openssh-clients postfixsudo
sudo systemctl enable sshd
sudo systemctl start sshd
sudo firewall-cmd --permanent --add-service=http
sudo systemctl startfirewall-cmd --permanent --add-service=https
sudo systemctl reload firewalld
sudo yum install postfix
sudo systemctl enable sshdpostfix
sudo systemctl enablestart postfix

STEP 2. Install GitLab

...

curl -sS https://packages.gitlab.com/install/repositories/gitlab/gitlab-ce/script.rpm.sh | sudo bash
sudo EXTERNAL_URL="http://127.0.0.1" yum install -y install gitlab-ce

Note that you can put your own URL instead of 127.0.0.1 above.

STEP 3.

...

Connect to your GitLab server by web browser

The default user account is root as administrator. You will be able to reset that administrator password.

Reference: https://about.gitlab.com/install/#centos-7?version=ce

You need to run vi /etc/gitlab/gitlab.rb and change external_url with the domain name 'gitlab.hakase-labs.co'.

external_url 'http://gitlab.hakase-labs.co'

STEP 4. Generate SSL

...