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;
  }
}

Answer 2

You can get your current IP address as shown here:

ifconfig en0 | grep inet | grep -v inet6 | awk '{print $2}'

Then you can use the --add-host flag with docker run:

docker run --add-host localnode:$(ifconfig en0 | grep inet | grep -v inet6 | awk '{print \$2}') ...

In your proxypass use localnode instead of localhost.

Answer 3

Yes. Docker needs to know about your host machine. You can set an alias to that with the --add-host switch. On a *nix box to create an alias to a name "localbox", this would be:

docker run my_repo/my_image --add-host=localbox:<host_name>`

On boot2docker it would be:

docker run my_repo/my_image --add-host=localbox:192.168.59.3`

where you should replace "192.168.59.3" with whatever boot2docker ip returns.

Then, you should access your host machine always through the alias localbox, so just change your nginx config to:

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

Answer 4

On linux, this works for me:

In the docker-compose.yml, mount an entrypoint script into the nginx container:

  nginx:
    image: nginx:1.19.2
    # ...
    volumes:
      - ./nginx-entrypoint.sh:/docker-entrypoint.d/nginx-entrypoint.sh:ro

The contents of the entrypoint map a local address to the host local address.

apt update
apt install iproute2 -y
echo "`ip route | awk '/default/ { print $3 }'`\tdocker.host.internal" >> /etc/hosts

Then, instead of using localhost inside the container, you can use docker.host.internal.

Answer 5

I had the same problem. Fixed it by using the local ip address of the docker host, instead of localhost.

So if the local ip address of your docker host in your LAN is 192.168.2.2:

  location / {
    proxy_pass http://192.168.2.2:3000;
  }

Of course this solution only works well if you have assigned a static ip to your docker host.

Answer 6

And finally, if you are using Nginx as a reverse proxy for multiple services, you can spin all of that with docker-compose. Make sure to expose ports “80:80” only on the Nginx service. Other services you can expose only the service port without mapping to the underlying network like so:

web:
.....
    expose:
       - 8080
nginx:
.....
    port:
        - “80:80”

and then use Nginx configuration proxy_pass http://service-name:port You don’t need the upstream app part at all