My situation is the following:
I am having a docker image/container in which I am compiling. I had to install some components to $HOME via the Dockerfile (so while creating the image).
Let's say one of those components is in ~/.config, but also other folders.
I would like to have the possibility to override the files in .config by mounting a home folder from the host on top of the one inside docker. Whenever you place a file in the mounted folder, it overrides the one which is already inside the container.
So in theory, this is exactly what an OverlayFS does, right? While the lower directory would be the one inside the Docker container, the upper directory would be the one on my Host.
Is there a way to accomplish that?
Until now I found the following related topics:
https://serverfault.com/questions/841238/how-to-use-overlayfs-with-docker-volumes
Drawback: The answer does only show how to use overlayfs on the host, but getting acccess to the lower container/image directory is not that self-explaining and also feels dirty.
Can I mount docker host directory as copy on write/overlay?
Drawback: Using mount -t overlay inside docker does not work on newer kernels because of the disabled overlay-on/over-overlay option
I also thought about manipulating the docker files on host directly, i.e. the directories where docker stores the files, but that feels a bit dirty.
To do so, I would declare VOLUME /home/user at the end of the Dockerfile. Then I would find my files of that directory in /var/lib/docker/volumes/user/_data. I could then create a overlayfs on my host, using that directory as lower, my other folder as upper. I could then remount that new directory using docker run --volume. Unfortunately this would involve su rights to access the /var/lib directory.
The other way around would be to bind-mount single files, but that's maybe a bit hackish too.
Related
Is it possible to bind mount a directory to a docker container where changes do not persist. It should be like:
All existing files in the directory are visible as in a regular bind mount, but
Changes (on files) made from the container are only visible to the container and not actually written to mounted directory.
It is like tmpfs like layer on top of normal bind mount.
It can be used for a lot of things like sand-boxing, or dry-running tests. This can also be used for running a container without filesystem of its own, like mounting root filesystem of the host system and for example install something with apt and try without affecting the host.
I am currently running a docker container with a specific folder shared to it. However, I need to access other folders which are not in the shared folder.
Does docker mount or docker volume help in any way to mount a file into a running docker container?
You can do this in two ways.
just copy the file and paste it the shared location, it will be available for use in docker mount location.
copy the host file to the container where you want, using
docker cp your_local_file containerid:/path/to/container
There are other ways around but that will not be that easy as these two approaches.
You can check this details article but I think it will take your handsome time to that each and every time.
mount-volumes-into-a-running-container
You can also check
docker-mount-dynamic-volumes/
I was thinking one alternative could be to use soft links by placing them inside your mounted volume but it won't work as documented in this post. A suggested alternative is to mount your folders as different volumes:
-v /home/test/:/home/test -v /mnt/mountedfile:/mnt/mountedfile
I have a little problem with the docker.
I'm trying to use a volume share with my computer. I can see the files on my computer, but they are empty from my container.
I tried to create a file in the /root of my container (outside the shared volume) and I can see the file without any problem.
If I do echo test > test.txt (in my shared volume), the file content is empty.
I execute this command :
docker run -v "D:\My App:/home/app" -it MyImage /bin/bash
In the /home/app folder, I can see the files on my computer. But if I do:
cat /home/app/test.txt
It tells me there's nothing in the file. While there is a text (the file exists)
If I create a file from my container, in the shared volume, I find it on my computer (and it is not empty).
If I create a file from my computer, I find it in the container, but it is empty when I try to display it.
Currently, when I do a cat test.txt, it doesn't display anything.
This should display this is a test
Do check first your Docker for Windows settings:
If your D:\ drive is not shared, you won't see much in your container.
docker/for-win issue 25 points out multiple possible issues:
If you are using Docker Toolbox:
In my case Docker Toolbox created a VM named default in Virtualbox and I added the Shared Folder in the VM; Virtualbox -> default (VM) -> Settings -> Shared Folders -> Add:
Then you can specify the paths in both your machine and the mapped path in the VM, like:
The 1st field is the path in your machine, like D:\my\app
The 2nd is the path in the VM, like /my-vm/app
Choose to Mount Automatically
Another:
One of the issues I had when learning, was to try and mount a volume in my container, but then have a folder that conflicted.
For example, I'd make my workingdir /foo/bar, then try to use a volume for /foo/bar/private as well, BUT already have a folder called private in my initial mount.
I would see no error, but I'd see the first folder and not my 2nd volume
Or:
docker/for-win issue 2151: "Volumes mounted from a Linux WSL instance don't resolve in container".
It refers to "how to use Docker with WSL".
The last thing we need to do is set things up so that volume mounts work. This tripped me up for a while because check this out…
When using WSL, Docker for Windows expects you to supply your volume paths in a format that matches this: /c/Users/nick/dev/myapp.
But, WSL doesn’t work like that. Instead, it uses the /mnt/c/Users/nick/dev/myapp format.
Honestly I think Docker should change their path to use /mnt/c because it’s more clear on what’s going on, but that’s a discussion for another time.
I am using docker for software development, as I can bundle all my dependencies (compilers, libraries, ...) within a nice contained environment, without polluting the host.
The way I usually do things (which I guess is pretty common): I have a directory on the host that only contains the source code, which is mounted into a development container using a docker volume, where my software gets built and executed. Thanks to volumes being in sync, any changes in the source is reflected within the container.
Here is the pitfall: when using a code editor, software dependencies are considered broken as they are not accessible from the host. Therefore linting, etc... does not work.
I would like to be able to mount, let's say /usr/local/include from the container onto the host so that, be correctly configuring my editor, I can fix all the warnings.
I guess docker volume is not the solution here, because it would override the contained file system...
Also, I'm using Windows (no choice here) therefore my flow is:
Windows > Samba > Linux Host > Docker > Container
and I'd prefer not switching IDE (VS Code).
Any ideas? Thank you!
You basically wish you could reverse mount a volume from the container to the host. This is unfortunately not possible with Docker, and there are variants of this question here: How to mount a directory in docker container to host
You're stuck with copying the files from the container to the host. As far as the host path matching /usr/local/include or having to use a different folder depends upon your setup.
The easiest solution which would not require changing the docker image would be to use docker cp to copy the files.
Otherwise, you could automate this by having the image on entry (after installing all dependencies) copy the files to /tmp/include and mount a host volume to that location.
I use https://forums.docker.com/t/how-to-mount-docker-volume-along-with-subfolders-on-the-host/120482/13 to expose python libraries from inside the container to a folder locally so that neovim can read the libraries for autocomplete/jump to definitions.
I am still relatively new to Docker, so I haven't quite figured out all the nuances yet, so forgive me if this has already been resolved elsewhere.
I would like to share files between the container and the host.
So far I have been using volumes, and mounting a specific host directory to a container directory - but this presents an issue in that, if the host directory is messed around with, these changes are also present in the container.
Another problem I am experiencing is that if the host directory is empty, and is mounted to a pre-existing directory on the container, then the contents of the directory are made invisible. I do understand that this behaviour is consistent with mounting, so I know this is not technically an issue.
But I wonder if it would be possible to set up a volume, or an alternative solution, that:
firstly cannot be edited on the host side,
and secondly allows for the host directory contents to be merged with the container's directory?
I wonder if it would be possible to set up a volume, or an alternative solution, that
firstly cannot be edited on the host side,
That would be a data volume container (with docker create on an image with a VOLUME directive)
and secondly allows for the host directory contents to be merged with the container's directory?
Not that I know of. You would have to do some kind of copy on startup.