adminMongo | Web based user interface to handle all your MongoDB | Database library

I'm a little bit lost with Docker. I try to start my NodeJS app via PM2 process manager. The general syntax is pm2 start app.js.

This works: First logging into the running docker container:
docker exec -it mongodb-plus /bin/bash
Then inside the container, run pm2:
root@367a1f9d1XXX:/# pm2 start app.js

This fails: But when I try to reach the same effect without the interactive terminal session:
docker exec mongodb-plus /bin/bash -c "pm2 start app.js"

...it fails with bash: pm2: command not found

Question: Why can't bash find the pm2 executable for the second variant?

For reference - my Dockerfile. (It's based on the mongo image, then install adminMongo.):

I have a container with 2 subnets:

• one is the reverse proxy subnet
• the second one is the internal subnet for the different containers of that project

The container needs to access an external SMTP server (on mailgun.com), but it looks like, with docker-compose, you can put a container on both one or more subnets and give it access to the host network at the same time.

Is there a way to allow this container to initiate connections to the outside world?

and, if no, what common workarounds are used? (for example, adding an extra IP to the container to be on the host network, etc.)

This is the docker compose file:

I encounter the error below when running docker-compose up