I recently had to migrate a working application to a RHEL7 server with SELinux enabled. Everything seemed to be okay but it just wouldn't connect to the remote database.
My first instinct was to troubleshoot the database server but I didn't have any problems connecting from a desktop client or from the terminal. After googling around for a while, it turned out that SELinux was the culprit. The easy (but inappropriate) solution was to disable it:
sudo setenforce 0
However, after a bit more research I learnt that there is a specific property that needed to be enabled:
sudo setsebool httpd_can_network_connect_db 1
That was it. Until I rebooted the server and the above reverted to off again. The final solution was:
sudo setsebool -P httpd_can_network_connect_db 1
The -P flag makes the change permanent. Problem solved.