Support PORT from environment variable

[ronakbanka]

Why

As of now there is no way to specify port using environment variable , which is used for most of cloud platform , eg heroku , cloudfoundry.

Changes

• Provision to use PORT from environment variable.
• Add UI message for server start along with PORT in use

[mtojek]

Hi Ronak,

thank you for contributing. Unfortunately I can't accept this PR because you simply ignored original command line arg because of introducting PORT env variable. That's not how it works.

Btw. you can still run the app binary like this and I'm pretty sure that's doable on Heroku ;) :

$ export PORT="9002"
$ greenwall -hostPort ":$PORT"

I'll close this PR and leave a issue for an alternative config source.

[ronakbanka]

simply ignored original command line arg because of introducting PORT env variable

If env variable is not defined , this will still respect commandline hostPort

if len(serverPort) == 0 {
		addr = httpServer.applicationConfiguration.HostPort
	}

case 1. when env port is defined

[ronak.banka greenwall (support_env_port)]$ PORT=8081 greenwall
Start listening on :8081

case 2. when env port is not defined

[ronak.banka greenwall (support_env_port)]$ greenwall
Start listening on :9001

case 3. when port is defined using cli flag

[ronak.banka greenwall (support_env_port)]$ greenwall -hostPort ":8082"
Start listening on :8082

you can still run the app binary like this and I'm pretty sure that's doable on Heroku

greenwall -hostPort ":$PORT"

This will work, without need to export

There should be a switch in command line args which will force the application to read config entirely from env vars.( from issue)

I haven't seen this practice for forcing environment var load by using additional flag, can you point to some project which uses this practice for golang based cli's?

[mtojek]

@ronakbanka I abandoned the idea of additional switch for env. Now ENV variables have the priority. Fixed here: #5