Connect to mongodb move from docker container

So I want to connect to my mongodb running on my host machine (DO droplet, Ubuntu 16.04). It works 27017

by default on local 27017

.

I then use mup to deploy a Meteor app on a DO blob, which uses Docker to run a Meteor app inside a container. So far, so good. The standard mongodb://...

connection url is used to connect the app to mongodb. Now I have the following problem:

mongodb://...@localhost:27017...

obviously does not work inside a docker container since it is localhost

not localhost.

I've already read a lot of posts about this and I've already tried using:

• --network="host"
  
  - didn't work, as it was said 0.0.0.0:80
  
  already used or something like that (nginx proxy)
• --add-host="local:<MY-DROPLET-INTERNET-IP>"
  
  and connect via mongodb://...@local:27017...
  
  : also doesn't work, since I can only access my mongodb from localhost, not from public IP

This should be a common problem!

tl; dr - How do I properly expose localhost

host hosts inside a docker container so that I can connect to services running on the host? (including their ports, for example 27017).

I hope someone can help!