[OpenShift] Deploy PHP/MySQL in OpenShift got 503 Service Temporarily Unavailable / 504 Gateway Time-out

Context :

The objective is to deploy the connection of MySQL with PHP in an OpenShift Server.
OpenShift is PaaS provided by Red Hat. For more info, read wikipedia OpenShift.

Problem :

The server returns :

503 Service Temporarily Unavailable

or

504 Gateway Time-out