DBMS は PostgreSQL とする。
RDS なら ここで PostgreSQL のインストールは不要。

rbenv + ruby-build をインスコする(Ubuntu, CentOS) | | Beyond Future Yak Shaving

sudo yum -y install tmux
sudo yum -y update && sudo reboot

sudo yum -y groupinstall "Development Tools"
sudo yum -y install openssl-devel zlib-devel readline-devel git
# If you need.
# TBD
# If you need.
sudo yum -y install postgresql-server postgresql-devel
sudo yum -y install nginx

CentOS7 LC_CTYPE: cannot change locale (UTF-8): No such file or directory - Qiita

-bash: warning: setlocale: LC_CTYPE: cannot change locale (UTF-8): No such file or directory

/etc/environment

LANG=en_US.utf-8
LC_ALL=en_US.utf-8