docker-compose named volume copy contents on initial start - docker

Question

I may be a little confused on how volumes work and I keep reading the same things over and over and to me it should be working. I want the contents from a folder inside the container to copy over if the volume gets initialized the first time.
I have something like this:
I have a Dockerfile like this:
https://github.com/docker-library/tomcat/blob/f6dc3671bf56465917b52c8df4356fa8f0ebafcd/7/jre7/Dockerfile
And before
EXPOSE 8080
CMD ["catalina.sh", "run"]
I have something like
Tomcat Dockerfile
VOLUME ["/opt/tomcat/conf"]
EXPOSE 8080
CMD ["catalina.sh", "run"]
When i build this image, I tag it as tomcat.
Then I have another Dockerfile with a bunch of environment variables that I set and a script.
Like so:
MyApp Dockerfile
FROM tomcat
ENV SOME_VAR=Test1
COPY assets/script.sh /script.sh
The second image builds from the first image and just adds a script and sets some settings. So far so good.
I want to do something like this in my docker-compose.yml file:
Docker Compose file
website:
image: myapp
ports:
- "8000:8080"
volumes:
- /srv/myapp/conf:/opt/tomcat/conf
I want the contents of /opt/tomcat/conf to copy into /srv/myapp/conf when that folder first gets created. Everything I read suggests that this should work, but it just creates the folder and doesn't copy the contents. Am I missing something here?
Basically I have this issue:
https://github.com/moby/moby/issues/18670
Oh and my docker-compose yaml file is using version 2.1 if that makes a difference.

Answer 1

What you are looking for is not possible when you are binding host volume inside the container. It will only work if you have a named volume. Then docker will copy the content of the folder to a container. You need to change you compose file to
version: '3'
services:
website:
image: myapp
ports:
- "8000:8080"
volumes:
- appconfig:/opt/tomcat/conf
volumes:
appconfig: {}
If you want to get the config out then you can use a shell script and your original compose file
#!/bin/bash
if [ ! -d "/srv/myapp/conf" ]; then
mkdir /srv/myapp/conf
docker create --name myappconfig myapp
docker cp myapp:/opt/tomcat/conf /srv/myapp/
docker rm myapp
fi
docker-compose up -d
For this to work the directory should not exist for the first time.