Dockerizing frontend app that relies on different custom node app

I want to dockerize the front end project I work on, but it relies on a different app, internal for the company, that is a combination of web server and proxy to our internal services.

So - what is the best approach here? To make two docker containers - one for the server/proxy dependency and expose the correct ports, and then another container for the frontend app?
Or to try to put both in one and the same container?

Running everything in separate containers is the preferred way. This is how you can make sure that every application has the best base image and you can upgrade everything without changing other containers.