how to reach another container from a dockerised nginx - nginx

Question

I have nginx in a docker container, and a nodejs webapp in another docker container.
The nodejs server is reachable from the host server on port 8080.
The nginx docker container is listening to port 80 (will do the certificate later, first this base must be working).
And now I want a subdomain to be forwarded to this 8080 nodejs app. lets say app1.example.com
From outside I can reach the app by the server ip (or hostname) and port 8080 but not on app1.example.com. And it does work on app1.example.com:8080 (I have opened up port 8080 on the host server).
I get a bad gateway nginx message when approaching the app1.example.com So I get in the first nginx container, but how do i get back to the host server to proxy pass it to the port 8080 of the host server (and not port 8080 of the nginx container). looking for the reverse EXPOSE syntax.
the main problem is, of course if I use the ip and port 127.0.0.1:8080 it will try on the nginx container....
So how do I let the nginx container route back to the host 127.0.0.1:8080?
I have tried 0.0.0.0 and defining an upstream, actually been googling a lot, and have tried a lot of configurations... but not yet found a working one....
Edit
Just found out, this command of docker might help:
sudo docker network inspect bridge
This shows the Ip address used inside the containers (in my case 172.17..0.2), but not sure this address stays the same every time the docker will restart... (e.g. server reboot)
Edit
Following alkaline answer I now have (but still not working):
my docker-compose.yml file:
version: "2"
services:
nginx:
container_name: nginx
image: nginx_img
build: ../docker-nginx-1/
ports:
- "80:80"
networks:
- backbone
nodejs:
container_name: nodejs
image: merites/docker-simple-node-server
build: ../docker-simple-node-server/
networks:
- backbone
expose:
- 8080
networks:
backbone:
driver: bridge
and my nginx (skipped the include in the conf.d folder for simplicity):
worker_processes 1;
events { worker_connections 1024; }
http {
sendfile on;
upstream upsrv {
server nodejs:8080;
}
server {
listen 80;
server_name app1.example.com;
location / {
proxy_pass http://upsrv;
}
}
}
edit 31-08-2016
this might be the problem, the name is not backbone, but called after the folder started the service from:
sudo docker network ls
out puts:
NETWORK ID NAME DRIVER SCOPE
1167c2b0ec31 bridge bridge local
d06ffaf26fe2 dockerservices1_backbone bridge local
5e4ec13d790a host host local
7d1f8c32f259 none null local
edit 01-09-2016
It might be caused by the way I have my nginx docker container setup?
this is the docker file I used:
############################################################
# Dockerfile to build Nginx Installed Containers
# Based on Ubuntu
############################################################
# Set the base image to Ubuntu
FROM ubuntu
# File Author / Maintainer
MAINTAINER Maintaner Name
# Install Nginx
# Add application repository URL to the default sources
# RUN echo "deb http://archive.ubuntu.com/ubuntu/ raring main universe" >> /etc/apt/sources.list
# Update the repository
RUN apt-get update
# Install necessary tools
RUN apt-get install -y nano wget dialog net-tools
# Download and Install Nginx
RUN apt-get install -y nginx
# Remove the default Nginx configuration file
RUN rm -v /etc/nginx/nginx.conf
# Copy a configuration file from the current directory
ADD nginx.conf /etc/nginx/
# Append "daemon off;" to the beginning of the configuration
RUN echo "daemon off;" >> /etc/nginx/nginx.conf
# Expose ports
EXPOSE 80
# Set the default command to execute
# when creating a new container
CMD service nginx start
My final solution 1th sept. 2016
I used this compose file now:
version: "2"
services:
nginx:
image: nginx
container_name: nginx
volumes:
- ./nginx-configs:/etc/nginx/conf.d
ports:
- "80:80"
networks:
- backbone
nodejs:
container_name: nodejs
image: merites/docker-simple-node-server
build: ../docker-simple-node-server/
networks:
- backbone
expose:
- 8080
networks:
backbone:
driver: bridge
In the project folder, from which you run docker-compose up -d, I added a folder named nginx-configs. This folder will 'override' all the files in the nginx container named /etc/nginx/conf.d
Therefor I copied the default.cfg from the nginx container before I added this volume mount. using the command:
docker exec -t -i container_name /bin/bash
and than cat /etc/nginx/conf.d/default.conf
and added the same default.conf in the project folder with nginx configs.
Besides the default I added app1.conf with this content:
upstream upsrv1 {
server nodejs:8080;
}
server {
listen 80;
server_name app1.example.com;
location / {
proxy_pass http://upsrv1;
}
}
This way, I can easily add a second app... third and so on.
So the basics is working now.

Answer 1

Here's a best practice. Only expose port 80 outside of the host. The nodejs app can be in a private network only accessible through nginx.
version: "2"
services:
nginx:
...
ports:
- "80:80"
networks:
- backbone
nodejs:
...
networks:
- backbone
expose:
- 8080
networks:
backbone:
driver: bridge
In your nginx.conf file, the upstream servers can be listed as nodejs:8080. The docker daemon will resolve it to the correct internal ip.