I want to achieve the following with Docker: I want to give a container access to a host directory, such that the container can make changes, but the changes are discarded once the container is exiting/removed (pretty much like an overlayfs).
Simply mounting the directory as a volume for the docker container seems like the wrong way to me, since changes made to a volume persist and I don't want that.
How do I tackle this problem?
The only way for a container to modify the host is to mount a directory between the host and the container. But the changes made by host or container will persist.
You could try the other way: COPY the files you want from host to container using a Dockerfile. The files will be only on the container. When you remove and launch another one, the new container will start with the original files.
Related
I'm kind of stuck,
I have a docker container that is running, and that container runs some elasticsearch inside.
But I forgot to use volume on the first deploy. So my container has lots of data inside, in a single folder in /app/data.
I would like to use the same container but use volume on that folder, without losing data inside...
So it will be possible to rebuild other containers to use the same volume.
Have you some tips to share?
The important thing is not to remove your container, or you'll lose all that data. I think docker cp is your friend here (docs here). Copy the data to the host, then start another container with a volume.
Once you've secured your data, you can stop and remove the first container.
If I do something like
docker run -v /opt/datadir:/var/lib/mysql image
I am mapping some location inside the container to a location in the host.
How is this different to the command COPY used when writing a Dockerfile?
The major difference is seen in case we edit any of the file present inside that location.
Suppose the directory /opt/datadir contains a file temp.txt
In case of bind mount, if you try to edit the file temp.txt from the host machine, the changes will be reflected inside the container and vice-versa.
When we create COPY command in Dockerfile, it copies the content to the filesystem of the container. Hence any changes done inside the container are DOES NOT affect the files present on the host machine.
In this case, if you want changes done on the host machine to be reflected inside the container, then you need to build a docker image and run a new container using the updated image.
When to use what?
For scenarios where the resource needs frequent updates, use bind mounts.
Eg: We want to provide our web server a configuration file that might change frequently.
In case the resource is independent of host filesystem, use COPY command inside dockerfile.
Eg: .tar, .zip, .war files or any file that requires no or very few updates inside the container.
I have a following question:
If changes on storage are persist between restartings of container ?
For example, we add some rows to mysql database and restart container. If added rows are present in database after restart ?
Yes they are. For each container you run, a docker volume (docker volume -ls to list them) is created.
However if you remove the container or create a new one for some reason, all the changes will be lost.
For a database, it is recommended to use shared volumes between host and the container, to be able to backup the data.
You can see which volume is used by your container using docker inspect.
HiTo persist the data between restartings of container, you need to mount a directory from host to the container so that it's visible to the container.
please check this how to share a directory for mysql which will help to you
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
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.