Q:

start a docker LAMP image with apache bound to non-standard port

I am new to docker, using https://github.com/mattrayner/docker-lamp 
I've read about the docker run command but still not quite getting the -p option. Is there a way to make it tell Apache to listen on a non-standard port?
I have succeeded in starting it on the default port 80, then re-configuring/re-loading Apache, from within the container, to bind itself to port 8080. But in that scenario I can't access the container's Apache from outside it via localhost:8080. (If that makes sense.) 
I simply want to develop something using PHP 5.6 without disturbing anything else on my local setup, which is running PHP 7.0. If there's another way to achieve the same end, I'm good with that too. 

A:

The -p or --publish option is a host:container port mapping specifically so that you don't have to change what may already be running inside the container.
If the container is already running on port 80 but you want to access it externally (via your host or laptop) via port 8080, then you can simple run with -p 8080:80 which will map your host port 8080 to the container port 80.
Multiple containers can run and use port 80 on the same host (since the containers have their own IP address on the Docker network). But you can only expose one port at a time.
For example, if you had 3 containers you wanted to run and all of them were listening on port 80, you could start the first with -p 8080:80, the second with -p 8082:80, and the third with -p 8084:80.
The -p section of https://docs.docker.com/engine/reference/commandline/run/#publish-or-expose-port--p---expose does into this a bit deeper.

