Configuring Nginx with Unicorn Flask within Docker - docker

Question

I'm having an issue configuring my nginx.conf for the container (server) container.
Without nginx: I can properly access the app through gunicorn.
With nginx: I get 502 Bad Gateway
My first question would be, should I even have nginx on the container(server) if I have ingress nginx?
My second question is, why is this configuration not working. Here is my docker file for container (server)
Dockerfile
FROM python:3 as builder
WORKDIR '/app'
COPY requirements.txt ./
RUN pip install -r requirements.txt
COPY . .
EXPOSE 8000
ENTRYPOINT [ "gunicorn", "-b", "0.0.0.0:8000", "run:app" ]
FROM nginx
EXPOSE 80
COPY ./nginx/default.conf /etc/nginx/conf.d/default.conf
nginx.conf
upstream flask_server {
server localhost:8000;
}
server {
listen 80;
server_name localhost;
location / {
proxy_pass http://flask_server;
proxy_set_header Host $host;
proxy_set_header X-Real-IP $remote_addr;
proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
}
}
Command
# build
docker build -t test/server .
# run
docker run -p 80:80 test/server
I suppose my issue is the upstream localhost is not working. When I'm developing locally is there no way for me to test this container specifically through docker? Or do I have to test locally with docker-compose and put nginx in a separate container?

Answer 1

I know, that post could be outdated, but it is still searching by Google :)
My second question is, why is this configuration not working. Here is my docker file for container (server)
So, as I can see, your specified proxy_pass as http://flask_server.
That means, flask_server hostname should be the resolvable name.
This name could be just the name of your Docker container, but your Dockerfile or docker run does not contain such options.
This name could be group of servers, but in this case, you have to define this directive
upstream flask_server {
server <hostname1>;
server <hostname2>;
}
(c) https://nginx.org/en/docs/http/ngx_http_proxy_module.html#proxy_pass
If a domain name resolves to several addresses, all of them will be used in a round-robin fashion. In addition, an address can be specified as a server group.
To sum up: to fix 502 error (which means connection timeout to the upstream) you can use 2 ways:
change proxy_pass http://flask_server; to proxy_pass http://0.0.0.0:8000;
OR
define upstream directive according manual
My first question would be, should I even have nginx on the container(server) if I have ingress nginx?
In my opinion - I should not.
You can deploy Nginx on the container(server) just in case you want (in the future) load-balance traffic between multiply gunicorn instances or want to provide some HTTP authentication or access restrictions.