...

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 firewall-cmd --permanent --add-service=https
sudo systemctl startreload firewalld
sudo yum install postfix
sudo systemctl enable sshdpostfix
sudo systemctl enablestart postfix

STEP 2. Install GitLab

GitLab provides an installer for adding the GitLab CE repository. You can do the necessary things by below command lines.

curl -sS https://packages.gitlab.com/install/repositories/gitlab/gitlab-ceee/script.rpm.sh | sudo bash
sudo yum -y install gitlab-ce

STEP 3. Configure GitLab URL

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

sudo yum -y install letsencrypt
letsencrypt certonly --standalone -d gitlab.hakase-labs.coEXTERNAL_URL="http://<your url>" yum install -y gitlab-ee

Reference: https://wwwabout.howtoforgegitlab.com/tutorial/how-to-install-and-configure-gitlab-ce-on-centos-7/install/#centos-7