I've installed Drupal on Red Hat 7 in Amazon Web Services, using a database on a separate RDS instance.
My original problem was that I couldn't make the Drupal installer recognize the /sites/default/ or /sites/default/files directories as writable, even after I confirmed they were writable by the ''apache'' user or temporarily set the permissions to writable by all. (This year-old issue may be similar.) When I filled in settings.php myself, then Drupal gave this connection error:
PDOException: SQLSTATE[HY000]  Can't connect to MySQL server on 'my-database-endpoint.rds.amazonaws.com' (13) in lock_may_be_available() (line 167 of /var/www/html/includes/lock.inc).
Disabling SElinux allows the installer to finish and allows Drupal to work. Re-enabling SElinux ('''setenforce 1''') stopped the installer; re-enabling SElinux after installation breaks Drupal, resulting in the same connection error given above. Drupal.org mentions the problem, but doesn't give a specific solution for this case.
I figure many other people must have run into the same problem when installing Drupal.
Obviously I have to re-enable SElinux, so does anyone already know how to modify SElinux configurations to enable Drupal to work properly (and not degrade security)?