Original question: How to use the VOLUME instruction in Dockerfile?
The actual question I want to solve is -- how to mount host volumes into docker containers in Dockerfile during build, i.e., having the docker run -v /export:/export capability during docker build.
The reason behind it, for me, is when building things in Docker, I don't want those (apt-get install) caches locked in a single docker, but to share/reuse them. That's the main reason I'm asking about this question.
Latest Update:
Before docker v18.09, the correct answer should be the one that starts with:
There is a way to mount a volume during a build, but it doesn't involve Dockerfiles.
However, that was a poorly stated, organized and supported answer. When I was reinstalling my docker contains, I happened to stumble upon the following article:
Dockerize an apt-cacher-ng service
https://docs.docker.com/engine/examples/apt-cacher-ng/
That's the docker's solution to this/my question, not directly but indirectly. It's the orthodox way docker suggests us to do. And I admit it is better than the one I was trying to ask here.
Another way is, the newly accepted answer, e.g., the Buildkit in v18.09.
Pick whichever suits you.
Was: There had been a solution -- rocker, which was not from Docker, but now that rocker is discontinued, I revert the answer back to "Not possible" again.
Old Update: So the answer is "Not possible". I can accept it as an answer as I know the issue has been extensively discussed at https://github.com/docker/docker/issues/3156. I can understand that portability is a paramount issue for docker developer; but as a docker user, I have to say I'm very disappointed about this missing feature. Let me close my argument with a quote from aforementioned discussion: "I would like to use Gentoo as a base image but definitely don't want > 1GB of Portage tree data to be in any of the layers once the image has been built. You could have some nice a compact containers if it wasn't for the gigantic portage tree having to appear in the image during the install." Yes, I can use wget or curl to download whatever I need, but the fact that merely a portability consideration is now forcing me to download > 1GB of Portage tree each time I build a Gentoo base image is neither efficient nor user friendly. Further more, the package repository WILL ALWAYS be under /usr/portage, thus ALWAYS PORTABLE under Gentoo. Again, I respect the decision, but please allow me expressing my disappointment as well in the mean time. Thanks.
Original question in details:
From
Share Directories via Volumes
http://docker.readthedocs.org/en/v0.7.3/use/working_with_volumes/
it says that Data volumes feature "have been available since version 1 of the Docker Remote API". My docker is of version 1.2.0, but I found the example given in above article not working:
# BUILD-USING: ???????docker build -t data .
# RUN-USING: ?????????docker run -name DATA data
FROM ?????????busybox
VOLUME ???????["/var/volume1", "/var/volume2"]
CMD ??????????["/usr/bin/true"]
What's the proper way in Dockerfile to mount host-mounted volumes into docker containers, via the VOLUME command?
$ apt-cache policy lxc-docker
lxc-docker:
Installed: 1.2.0
Candidate: 1.2.0
Version table:
*** 1.2.0 0
500 https://get.docker.io/ubuntu/ docker/main amd64 Packages
100 /var/lib/dpkg/status
$ cat Dockerfile
FROM debian:sid
VOLUME ["/export"]
RUN ls -l /export
CMD ls -l /export
$ docker build -t data .
Sending build context to Docker daemon 2.56 kB
Sending build context to Docker daemon
Step 0 : FROM debian:sid
---> 77e97a48ce6a
Step 1 : VOLUME ["/export"]
---> Using cache
---> 59b69b65a074
Step 2 : RUN ls -l /export
---> Running in df43c78d74be
total 0
---> 9d29a6eb263f
Removing intermediate container df43c78d74be
Step 3 : CMD ls -l /export
---> Running in 8e4916d3e390
---> d6e7e1c52551
Removing intermediate container 8e4916d3e390
Successfully built d6e7e1c52551
$ docker run data
total 0
$ ls -l /export | wc
20 162 1131
$ docker -v
Docker version 1.2.0, build fa7b24f
Question&Answers:
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