How to proxy Docker and non-Docker applications?

[EDIflyer]

Would be grateful for any guidance! I've got NPM set up and working nicely in a Docker container. I've got all my containers connected to the nginx-proxy-manager_default network and can successfully set up proxy hosts with SSL for subdomains for each of them.

However I'm now wanting to setup a webhook too. I'm tried using the Dockerised one from https://github.com/almir/docker-webhook but of course then found it can't run a script on the host machine due to security restrictions. It's based on https://github.com/adnanh/webhook so I installed that on the host machine and again it works well and is now able to run the script. However I don't want to expose the 9000 port and instead want to run it via NPM through an SSL reverse proxy - however I can't work out how to get NPM to redirect to something running on localhost on the host. If I try localhost or 127.0.0.1 it (understandably) just tried to connect to the NPM container!

I then had a look at the mention of host.docker.internal option available in Linux from Docker v.20.10 onwards. However it seems for this to work you need to connect the container to the Host network, which I can't do as NPM is connected to nginx-proxy-manager_default and needs to be on that to access all the other containers!

As I say any advice/guidance much appreciated!

[EDIflyer]

OK got there in the end! Played about a bit with some command line pinging and wgetting in alpine containers with different network settings and when I realised I could ping the address OK but couldn't get the service to worked I realised it might be a firewall rule issue - found this article and adding sudo ufw allow from 172.19.0.0/16 and then reverse proxying to 172.17.0.1 did the trick :)

https://superuser.com/questions/1709013/enable-access-to-host-service-with-ubuntu-firewall-from-docker-container