proxy'ing between docker containers - ruby-on-rails

Question

I have a docker setup with the following
rails api backend
mysql db
redis db
node/react frontend (webpack)
nginx serving the frontend
(the rails backend is currently being served through the builtin puma server - I think I will move it to the same nginx server runing the node app)
My problem is that the frontend will request stuff on the backend, but this does not work.
I have set up a proxy on nginx as follows:
#nginx.conf
server {
listen 8080;
# Always serve index.html for any request
location / {
# Set path
root /wwwroot/;
try_files $uri /index.html;
}
location /api/ {
proxy_pass http://127.0.0.1:3000;
}
}
But when I when I initiate an api call I get the following in the nginx log:
nginx-server | 2017/05/13 20:56:08 [error] 5#5: *19 connect() failed (111: Connection refused) while connecting to upstream, client: 172.21.0.1, server: , request: "POST /api/authenticate HTTP/1.1", upstream: "http://127.0.0.1:3000/api/authenticate", host: "localhost:8080", referrer: "http://localhost:8080/"
nginx-server | 172.21.0.1 - - [13/May/2017:20:56:08 +0000] "POST /api/authenticate HTTP/1.1" 502 575 "http://localhost:8080/" "Mozilla/5.0 (Macintosh; Intel Mac OS X 10_12_3) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/57.0.2987.133 Safari/537.36" "-"
And I do not see any thing hitting the puma server.
I am not sure where I should be looking. Is this a problem with my docker-compose file or is it a nginx issue (or both).
I have included my docker-compose.yml below:
version: '2'
services:
nginx:
build:
context: .
dockerfile: docker.nginx
image: pt-nginx
container_name: nginx-server
ports:
- "8080:8080"
volumes:
- wwwroot:/wwwroot
webpack:
build:
context: ./frontend
dockerfile: docker.webpack
image: pt-webpack
container_name: react-frontend
ports:
- "35729:35729"
volumes:
- ./frontend:/app
- /app/node_modules
- wwwroot:/wwwroot
db:
build:
context: ./backend
dockerfile: docker.mysql
image: pt-mysql
container_name: mysql-server
env_file: ./backend/.env
ports:
- "3306:3306"
volumes:
- ./sql/data/:/var/lib/mysql
redis:
build:
context: ./backend
dockerfile: docker.redis
image: pt-redis
container_name: redis-server
app:
build:
context: ./backend
dockerfile: docker.rails
image: pt-rails
container_name: rails-server
command: >
sh -c '
rake resque:start_workers;
bundle exec rails s -p 3000 -b 0.0.0.0;
'
env_file: ./backend/.env
volumes:
- ./backend:/usr/src/app
- /Users/mh/Pictures/ROR_PT/phototank:/Users/martinhinge/Pictures/ROR_PT/phototank
ports:
- "3000:3000"
expose:
- "3000"
depends_on:
- db
- redis
volumes:
wwwroot:
driver: local

Answer 1

The problem is that your nginx service is requesting upstream of localhost (127.0.0.1). But the application is in another container (with another IP). You can reference the rails application by DNS at appsince they are both in a default network. The upstream in nginx configuration would look something like proxy_pass http://app:3000; instead.
Read more about the networking at https://docs.docker.com/compose/networking/, specifically:
Within the web container, your connection string to db would look like postgres://db:5432, and from the host machine, the connection string would look like postgres://{DOCKER_IP}:8001.