This tutorial helps you to connect your RDS DB from docker container.
Use these commands to install "MariaDB/MysqlDB" on Container so you can run "mysql" command to connect your RDS.
cd /etc/yum.repos.d/
sed i 's/mirrorlist/#mirrorlist/g' /etc/yum.repos.d/CentOS*
sed i 's|#baseurl=http://mirror.centos.org|baseurl=http://vault.centos.org|g' /etc/yum.repos.d/CentOS*
yum update -y
yum install -y mariadb