mjhjmtu

poking docker to see how it works:

ubuntu@ip-172-31-14-19:~$ 
ubuntu@ip-172-31-14-19:~$ sudo docker run --net=host -d -t jmar71n/freepbx
2792243260a8de33d1a775d115188e601fc556e500b5ad085e09b4133d0f3d06
ubuntu@ip-172-31-14-19:~$ 
ubuntu@ip-172-31-14-19:~$ sudo docker run -it jmar71n/freepbx bash
root@46f45b8973c3:/# 
root@46f45b8973c3:/# exit
exit
ubuntu@ip-172-31-14-19:~$ 
ubuntu@ip-172-31-14-19:~$ sudo docker run -it jmar71n/freepbx bash
root@813557bf8922:/# 
root@813557bf8922:/# echo $PS1
[e]0;u@h: wa]$debian_chroot:+($debian_chroot)u@h:w$
root@813557bf8922:/# 

Now, is each run a new instance? Is that why the prompt changes? The hostname is a unique ID for each run?

How would I login to the first instance, with --net=host?

When I try the exec flag, it fails:

ubuntu@ip-172-31-14-19:~$ 
ubuntu@ip-172-31-14-19:~$ sudo docker exec -it jmar71n/freepbx bash
Error: No such container: jmar71n/freepbx
ubuntu@ip-172-31-14-19:~$ 

Why? What's the correct way to login to that instance?

ubuntu@ip-172-31-14-19:~$ 
ubuntu@ip-172-31-14-19:~$ sudo docker images
REPOSITORY TAG IMAGE ID CREATED SIZE
ubuntu latest 20c44cd7596f 2 days ago 123MB
hello-world latest 725dcfab7d63 2 weeks ago 1.84kB
jmar71n/freepbx latest 8dda2a58fde1 19 months ago 1.54GB
ubuntu@ip-172-31-14-19:~$ 

Docker run, creates a new instance (para virtualised) environment from a given image.

To log in to a given instance, you need to run docker exec but you need to execute docker exec with the id of the container you are looking to log into. This can be attained from the command:

docker ps -a

Then with the id attained, log into the container with:

docker exec -it <containerid> bash

When you execute run command, you create new container each time.

You execute run with options -it so you are being connected inside docker container, that's why your prompt is changing. So, all commands you execute with a new prompt will be executed inside the container.

When you say exit you terminate your active process (bash since you pass it as a parameter during creation) and your container stops since it lives only as long as the main process with PID 1 lives.

In order to connect to the instance, first, run it with -d in detached mode and then you can run docker attach. docs You can get an ID of your container by docker ps -a. Same with docker exec -it <containerID> bash.