"Welcome to Nginx!" - Docker-Compose, using uWSGI, Flask, nginx

Question

My Problem:

I am using Ubuntu 18.04 and a docker-compose based solution with two Docker images, one to handle Python/uWSGI and one for my NGINX reverse proxy. No matter what I change, it always seems like WSGI is unable to detect my default application. Whenever I run docker-compose up, and navigate to localhost:5000 I get the above default splash.

The complete program appears to work on our CentOS 7 machines. However, when I try to execute it on my Ubuntu test machine, I can only get the "Welcome to NGINX!" page.

Directory Structure:

 /app
  - app.conf
  - app.ini
  - app.py
  - docker-compose.py
  - Dockerfile-flask
  - Dockerfile-nginx
  - requirements.txt
  /templates

(All code snippets have been simplified to help isolate the problem)

Here is an example of my docker traceback:

clocker_flask_1

[uWSGI] getting INI configuration from app.ini
current working directory: /app
detected binary path: /usr/local/bin/uwsgi
uwsgi socket 0 bound to TCP address 0.0.0.0:5000 fd 3
*** WARNING: you are running uWSGI as root !!! (use the --uid flag) ***
*** Operational MODE: preforking+threaded ***
WSGI app 0 (mountpoint='') ready in 1 seconds on interpreter 0x558072010e70 pid: 1 (default app)

clocker_nginx_1

/docker-entrypoint.sh: /docker-entrypoint.d/ is not empty, will attempt to perform configuration
/docker-entrypoint.sh: Looking for shell scripts in /docker-entrypoint.d/
/docker-entrypoint.sh: Launching /docker-entrypoint.d/10-listen-on-ipv6-by-default.sh
10-listen-on-ipv6-by-default.sh: Getting the checksum of /etc/nginx/conf.d/default.conf
10-listen-on-ipv6-by-default.sh: Enabled listen on IPv6 in /etc/nginx/conf.d/default.conf
/docker-entrypoint.sh: Launching /docker-entrypoint.d/20-envsubst-on-templates.sh
/docker-entrypoint.sh: Configuration complete; ready for start up

Here is my docker-compose.yaml:

# docker-compose.yml
version: '3'
services:
  
  flask:
    image: webapp-flask
    build:
      context: .
      dockerfile: Dockerfile-flask
    volumes:
      - "./:/app:z"
      - "/etc/localtime:/etc/localtime:ro"
    environment:
      - "EXTERNAL_IP=${EXTERNAL_IP}"

  nginx:
    image: webapp-nginx
    build:
      context: .
      dockerfile: Dockerfile-nginx
    ports:
      - 5000:80
    depends_on:
      - flask

Dockerfile-flask:

FROM python:3
ENV APP /app
RUN mkdir $APP
WORKDIR $APP
EXPOSE 5000
COPY requirements.txt .
RUN pip install -r requirements.txt
COPY . .
CMD [ "uwsgi", "--ini", "app.ini" ]

Dockerfile-nginx

FROM nginx:latest
EXPOSE 80
COPY app.conf /etc/nginx/conf.d

app.conf

server {
    listen 80;
    root /usr/share/nginx/html;
    location / { try_files $uri @app; }
    location @app {
        include uwsgi_params;
        uwsgi_pass flask:5000;
    }
}

app.py

# Home bit
@application.route('/')
@application.route('/home', methods=["GET", "POST"])
def home():
    return render_template(
        'index.html',
        er = er
    )

if __name__ == "__main__":
    application.run(host='0.0.0.0')

app.ini

[uwsgi]
protocol = uwsgi
module = app
callable = application
master = true
processes = 2
threads = 2
socket = 0.0.0.0:5000
vacuum = true   
die-on-term = true
max-requests = 1000

Robert Nubel Robert Nubel · Accepted Answer · 2020-11-17T03:56:21

The nginx image comes with a main configuration file, /etc/nginx/nginx.conf, which loads every conf file in the conf.d folder -- including your nemesis in this case, a stock /etc/nginx/conf.d/default.conf. It reads as follows (trimmed a bit for concision):

server {
  listen 80;
  server_name localhost;

  location / {
    root /usr/share/nginx/html;
    index index.html index.htm;
  }
}

So, your app.conf and this configuration are both active. The reason why this default one wins, though, is because of the server_name directive that it has (and yours lacks) -- when you're hitting localhost:5000, nginx matches based on the hostname and sends your request there.

To fix this easily, you can just remove that file in your Dockerfile-nginx:

RUN rm /etc/nginx/conf.d/default.conf

"Welcome to Nginx!" - Docker-Compose, using uWSGI, Flask, nginx

1 Answers