I would like to have a Docker container be able to copy files into a volume without being able to read its contents / know what files are inside of it.
The container should also be able to append contents to a file inside that volume.
Is there a way to achieve any of this by using Docker compose?
No, there is not. Docker volumes are mounted to the filesystem either read-write or read-only: https://docs.docker.com/storage/volumes/#use-a-read-only-volume.
Related
How do multiple containers(create from same image) access the directory(packaged in the image) in other container? There are some ways not elegant:
Mount directory into a shared volume or host path. When a container changed files in the directory, other containers will perceive it. Is there any idea to make shared volume working like copy-on-write?
Create a volume for each container, and copy directory into the volume. In this way, the directory have to save multiple copies in disk.
I've browsed this problem [https://stackoverflow.com/questions/29550736/can-i-mount-docker-host-directory-as-copy-on-write-overlay], I don't want containers to run in privileged mode. Is there a better idea?
Per design one container cannot access the files inside another container.
You will need to store the data outside of a container, then mount it via volume mount or bind mount. Alternatively you could try to perform some NFS/SMB/... mount of shared storage inside the container.
This is completely independent from running a container in host mode.
I have a docker container image that requires me to mount a volume containing a specific configuration file, in order for that container to properly start (this image is not one that I have control over, and is vendor supplied). If that volume is not mounted, the container will exit because the file is not found. So I need to put a configuration file in /host/folder/, and then:
docker run --name my_app -v /host/folder:/container/folder image_id
The application will then look in /container/folder/ for the file it needs to start.
I want to create/commit a new image with that file inside /container/folder/, but when that folder is mounted as volume from the host, docker cp will not help me do this, as far as I have tried. I think, as far as docker is concerned, the file copied there is no different than the files in the mounted volume, and will disappear when the container is stopped.
Part of the reason I want to do this, is because the file will not be changed, and should be there by default. The other reason is that I want to run this container in Kubernetes, and avoid using persistent volumes there to mount these directories. I have looked into using configmaps, but I'm not seeing how I can use those for this purpose.
If you can store the file into the ConfigMap you can mount the file to volume and use it inside the Kubernetes.
I am not sure with the type of file you have to use.
ConfigMap will inject this file into the volume of a POD so the application could access and use it.
In this case there will be no PVC required.
You can also follow this nice example showing how to mount the file into a volume inside a pod.
OR
Also, I am not sure about the docker image but if you can use that docker image you can add the file into the path, something like:
FROM <docker image>
ADD file ./container/folder/
In this case, you might have to check you can use the vendor docker image as a base and add the file into it.
I am trying to write content(backup files) into a temporary directory inside a running Docker container.
Is there a way to create a temporary directory inside the container and write content to it?
You can bind this folder to the docker container directly using volumes.
As you do not want them changed I assume you could mount them as a read-only volume.
In that case you do not have to copy them around as you will have them accessible already in the container :)
I have a Docker container and I am trying to make it so that all of the files in /var/www/ on the container will be saved on the host system at a location (/home/me), and vise-versa. Is it possible to have this shared space between the two?
Would you accomplish this with mount points, or is there a better method?
Thanks
You can use volumes for sharing between container and host.
docker run -v /home/me:/var/www <image>
If you have a fixed files/data, you can add to the image using dockerfile or committing after copying into container. If you want to share rw dir between host and container, you need to use the volumes. Your data will also be persisted even if you remove and recreate a new container.
There are three ways that you can do this
Use volumes. Official docs
Burn the files in your image. Basically include the creation of the files inside the Dockerfile. This means every container container from that image will have an initial state of sorts.
Use data-only containers. These are containers without a running process that contain the data that you need. This also uses volumes. But instead of mounting to the host, your containers mount on the data-only container (which in turn mounts on the host if you want to). This answer will be useful
Is it possible to perform commands in a dockerfile on a file which you are going to mount.
I want to build an image and every user who creates a container from that image is able to mount their own volume with the -v option.
Now my problem is the fact that I have to change the permission of that file inside my container. So I was wondering if it was possible to perform a chmod on that file (in my dockerfile) while that file wasn't mounted yet.
No, you have to do it when the file is already mounted.
What problem are you trying to solve?