node.js - How do I access a server on localhost with nginx docker container?

Question

I'm trying to use a dockerized version of nginx as a proxy server for my node (ExpressJS) application. Without any configuration to nginx and publishing port 80 for the container, I am able to see the default nginx landing page. So I know that much is working.

Now I can mount my sites-enabled directory that contains the configuration for proxy_pass localhost:3000. I have my node application running locally (not in any Docker container) and I can access it via port 3000 (i.e. localhost:3000). However, I would assume that with nginx container running, mapped to port 80, and proxying my localhost:3000, that I would be able to see my very simple (hello world) application. Instead I receive a 502.

Do I need to pass something into docker? Is this likely a nginx configuration error? Here is my nginx configuration:

server {
  listen 0.0.0.0:80;
  server_name localhost;

  location / {
    proxy_pass http://localhost:3000;
  }
}

I have tried using this question but it did not seem to help. That is unless I'm doing something completely wrong.

Answer 1

If you're using docker-for-mac 18.03 or newer it auto creates a special DNS entry host.docker.internal that dynamically binds to the host inet ip. You can then use the dns name to proxy services running on the host machine from inside a container as a stand-in for localhost.

i.e. an nginx config file:

server {
  listen 0.0.0.0:80;
  server_name localhost;

  location / {
    proxy_pass http://host.docker.internal:3000;
  }
}