When mounting /etc/nginx/ container doesnt run

Question

I want to mount the /etc/nginx folder to a custom folder on my host. However, whenever I try this the container doesn't run at all. Mounting anything else doesnt seem to be problem, though the folder I want it to mount to is always empty.

I tried using /usr/local/nginx/conf or /usr/local/etc/nginx instead of /etc/nginx but the folder is always empty. Though here the container runs at least. Which is what lead me to believe it is this specific mounting that is causing problems.

This is what I want to do.

docker run -p 80:80 -p 443:443 -v /home/pi/nginx_files/config:/etc/nginx -v /home/pi/nginx_files/certs:/etc/ssl/private -d nginx

The container seems to run with any other folder, as ive tried

docker run -p 80:80 -p 443:443 -v /home/pi/nginx_files/config:/etc/nginx/b -v /home/pi/nginx_files/certs:/etc/ssl/private -d nginx

Just to see if any non existent folder doesn't have that problem.

Before that I tried using docker composer and the docker-compose.yaml

version: '3'

services:
  reverse:
    container_name: reverse
    hostname: reverse
    image: nginx
    ports:
      - 80:80
      - 443:443
    volumes:
      - <path/to/your/config>:/etc/nginx
      - <path/to/your/certs>:/etc/ssl/private

and

tried docker-compose up

However it suffered from the same problem, where it doesn't even start the container. Error Message:

Creating network "nginx_files_default" with the default driver
Creating reverse ... done
Attaching to reverse
reverse    | 2019/08/31 00:41:07 [emerg] 1#1: open() "/etc/nginx/nginx.conf" failed (2: No such file or directory)
reverse    | nginx: [emerg] open() "/etc/nginx/nginx.conf" failed (2: No such file or directory)
reverse exited with code 1

If I use nonexistent folders it just gets stuck in "Attaching to reverse" indefinitely. But I dont get a message "no such file or directory" although the folders have completely made up names and definitely dont exist.

Did I missunderstand the point of mounting? I thought I'd get to look at the default.conf file by having the container save it on the host, but does it not create one? Do I have to create one myself and then mount it to the container? Does mounting create a folder to read from for the container and not a folder to write to? I'm fairly new to docker and linux so forgive me if this is a rather stupid question.

Answer 1

You should not mount the whole /etc/nginx directly, it will defiantly break you container because it will override the following files and directories.

conf.d fastcgi_params koi-utf koi-win, mime.types modules nginx.conf scgi_params uwsgi_params and win-utf

Without going into details of each directory, just take mime.types it will be overridden as a result, your Nginx will never be able to run without /etc/nginx/mime.types

If you want to update configuration then you should only mount

/etc/nginx/conf.d

For example

docker run -p 80:80 -p 443:443 -v /home/pi/nginx_files/config:/etc/nginx/conf.d -v /home/pi/nginx_files/certs:/etc/ssl/private -d nginx

If really want to update nginx.conf then you should mount exact file, not the whole directory

docker run -p 80:80 -p 443:443 -v /home/pi/nginx_files/config/nginx.conf:/etc/nginx/nginx.conf  -v /home/pi/nginx_files/certs:/etc/ssl/private -d nginx

Answer 2

As pointed out in the comments and @Adiii's answer, you should avoid bind-mounting a directory to /etc/nginx/ as you're "overriding" the containers configuration (think of it as mounting a USB device to a folder that already contains files, a ls -alF will display the contents of the USB device and the files that exist in the mount point will only be available once the USB device is unmounted).

You can pull the nginx.conf and default.conf from an instance of a running container for example:

1. run a nginx container: docker run --rm -d --name nginx nginx:1.17.3
2. use docker cp to copy out the files: docker cp nginx:/etc/nginx/nginx.conf /path/to/nginx.conf and docker cp nginx:/etc/nginx/conf.d/default.conf /path/to/default.conf
3. stop the container: docker stop nginx (the container will be removed given the --rm from the docker run)

You can then modify the configuration files and bind mount them in the container i.e.: docker run --rm -d --name nginx -v /path/to/nginx.conf:/etc/nginx/nginx.conf nginx:1.17.3

Otherwise you can build your own image using your custom configuration, for example:

├── default.conf
├── Dockerfile
└── nginx.conf

FROM nginx:1.17.3

COPY nginx.conf /etc/nginx/nginx.conf
COPY default.conf /etc/nginx/conf.d/default.conf

You can build your image: docker build --rm -t so:57734446 . and run it: docker run --rm -d --name my-nginx so:57734446. For a little more advanced use-case of the image this is my nginx-modsecurity build that extends the official nginx image.