Affects Version/s: None
Fix Version/s: None
It allow the tasks to know the port the app should listen on.
Used with https://github.com/mesosphere/marathon/blob/master/bin/haproxy_cfg or https://github.com/Wizcorp/frontrunner, the tasks are aware of the port used by the proxy/load balancer.
The PORTS, PORT, PORT0, ... variables contain the ports used by the task, which are backends for the proxy/lb.
The APP_PORTS, APP_PORT, APP_PORT0, ... variables contains the port that the app should use, which is the port used by the proxy/lb.