Docker mounted volume not tracking nginx log files

Question

So I actually "solved" this issue right before posting this question, but I'll ask it anyway because I'd like to know why what I did works,

I have nginx installed via brew and the docker nginx base image in my local machine.

I have the directory /container/logs/nginx and I'm mounting it to /var/log/nginx that's inside of a docker container using

docker run -d -P -v /container/logs/nginx:/var/log/nginx nginx

I was expecting to see the access and error .log files in the mounted directory. However, nothing was there.

I thought maybe, even though there were no error messages, that there might be a permissions issue with mapping from a directory that resides in my root directory, so I instead mapped it to /Users/jimmygong/containers/logs/nginx , using

docker run -d -P -v /Users/jimmygong/container/logs/nginx:/var/log/nginx nginx

This does work. Could someone walk me through exactly what's occurring here? Do I not have write permissions outside of my home directory (eg /Users/jimmygong)? I'm running Mac OS.

Answer 1

This is because of the automount script of boot2docker - I am assuming you are using boot2docker since you are using brew and your user dir starts with /Users . That and the fact you also need to tell virtualbox to expose your shared directory.

Imagine how your volume is shared:

your mac <--X--> boot2docker VM <----> nginx container
            \_ /Users is mounted properly, but not other dir.

see:

• Boot2Docker on Mac - Accessing Local Files
• https://github.com/boot2docker/boot2docker/blob/master/rootfs/rootfs/etc/rc.d/automount-shares
• https://github.com/boot2docker/boot2docker/issues/678
• Mount volume to Docker image on OSX