You need multiple database systems to run GitLab, which may sound unusual, but they are very different databases.
MySQL is used for long-term storage of data, where Redis is responsible for queueing up the jobs, distributing them over several processes, and to ensure fast response time.
We will go through the following steps to install MySQL for GitLab:
Installing the MySQL server is easy and is followed by creating a dedicated user for GitLab.
Do not just use a common user or even root to do this, it's a potential security vulnerability.
sudo apt-get ...