Docker and NGINX - host not found in upstream when building with docker-compose

Question

I am attempting to use an NGINX container to host a static web application. This container should also redirect certain requests (i.e. www.example.com/api/) to another container on the same network.

I am getting the "host not found in upstream" issue when calling docker-compose build, even though I am enforcing that the NGINX container is the last to be built.

I have tried the following solutions:

Enforcing a network name and aliases (as per Docker: proxy_pass to another container - nginx: host not found in upstream)
Adding a "resolver" directive (as per Docker Networking - nginx: [emerg] host not found in upstream and others), both for 8.8.8.8 and 127.0.0.11.
Rewriting the nginx.conf file to have the upstream definition before the location that will redirect to it, or after it.

I am running on a Docker for Windows machine that is using a mobylinux VM to run the relevant container(s). Is there something I am missing? It isn't obvious to me that the "http://webapi" address should resolve correctly, as the images are built but not running when you are calling docker-compose.

nginx.conf:

user  nginx;
worker_processes  1;

error_log  /var/log/nginx/error.log warn;
pid        /var/run/nginx.pid;


events {
    worker_connections  1024;
}


http {
    include       /etc/nginx/mime.types;
    default_type  application/octet-stream;


    log_format  main  '$remote_addr - $remote_user [$time_local] "$request" '
                      '$status $body_bytes_sent "$http_referer" '
                      '"$http_user_agent" "$http_x_forwarded_for"';

    access_log  /var/log/nginx/access.log  main;

    sendfile        on;
    #tcp_nopush     on;

    keepalive_timeout  65;

    #gzip  on;

    upstream docker-webapi {
        server webapi:80;
    }

    server {
        listen       80;
        server_name  localhost;

        location / {
            root /wwwroot/;
            try_files $uri $uri/ /index.html;
        }

        location /api {
            proxy_set_header Host $http_host;
            proxy_redirect off;
            proxy_pass http://docker-webapi;
            proxy_set_header   X-Real-IP $remote_addr;
            proxy_set_header   X-Forwarded-For $proxy_add_x_forwarded_for;
            proxy_set_header   X-Forwarded-Host $server_name;
        }

        error_page   500 502 503 504  /50x.html;
            location = /50x.html {
            root   /usr/share/nginx/html;
        }
    }
}

docker-compose:

version: '3'

services:
  webapi:
    image: webapi
    build:
      context: ./src/Api/WebApi
      dockerfile: Dockerfile    
    volumes:
        - /etc/example/secrets/:/app/secrets/
    ports:
      - "61219:80"

  model.api:
    image: model.api
    build:
      context: ./src/Services/Model/Model.API
      dockerfile: Dockerfile
    volumes:
        - /etc/example/secrets/:/app/secrets/
    ports:
      - "61218:80"

  webapp:
    image: webapp
    build:
      context: ./src/Web/WebApp/
      dockerfile: Dockerfile
    ports:
      - "80:80"
    depends_on:
        - webapi

Dockerfile:

FROM nginx

RUN mkdir /wwwroot
COPY nginx.conf /etc/nginx/nginx.conf
COPY wwwroot ./wwwroot/
EXPOSE 80
RUN service nginx start

Do you have a nginx -t to verify the config in your build? If so you shouldn't have it. Those will only be useful when the environment is up — Tarun Lalwani
@TarunLalwani Nope, not explicitly. I added the Dockerfile to the post. — José Maia
@whites11 Yes, immediately upon calling the docker-compose build or docker-compose up --build commands, the first two images are built and the webapp image fails on the last step. — José Maia

Tarun Lalwani Tarun Lalwani · Accepted Answer · 2017-08-28T19:37:47

You issue is below

RUN service nginx start

You never run service command inside docker, because there is no init system. Also RUN commands are run during build time.

nginx original image has everything you need for nginx to start fine. So just remove the line and it would work.

By default nginx image has below CMD instruction

CMD ["nginx" "-g" "daemon off;"]

You can easily find that out by running the below command

docker history --no-trunc nginx | grep CMD

Docker and NGINX - host not found in upstream when building with docker-compose

1 Answers