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
Related
We have a system in which the user can start sessions inside a number of docker containers. When they do this their home directory is automatically mounted to the docker container. We can't modify the system which starts the docker containers and mounts the directory.
Our goal is to have one image not automatically mount this container. Is there something that I can do to the image to basically make one directory unmountable?
No. If you can docker run a container, you can always use docker run -v to mount any host directory over any directory, and the original contents of the image will be hidden.
Docker's general model is that the image has somewhat limited powers, but you can specify most things when you start the container. Trying to prevent a volume mount (more frequently asked, trying to force a volume mount) is the opposite of this model; the image has no way to prevent how it will eventually be used.
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'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.
Instead of using a data-only container, I can ...
create a directory on the host (say /opt/shared_data)
Run every container with -v /opt/shared_data:/some/mount/point_inside/container
voila, now /opt/shared_data is effectively shared amongst all containers , correct?
If my understanding is correct, if I create a data-only container and then use "--volumes-from" when running other containers, I am stuck mounting them in the same location they were mounted, whereas, this way I get to choose which directory they are mounted as in my containers.
So why do I need "data-only" containers? Besides, the volume just points to somewhere on the host (/var/lib/docker/volumes?) which is functionally equivalent to my /opt/shared_data anyway right? Whats the advantage of the former?
Data containers have been largely deprecated in favor of named volumes. There's really no advantage to using a data container over a named volume, and includes the disadvantage of being stuck with the mount points.
To compare named volumes with host volumes (aka bind mounts), you have have a few differences:
Host volumes include permission issues, users inside the container will differ from those outside the container and files may not be easily accessed from both environments
Named volumes add the ability to use any volume driver so you can mount your data from remote locations.
Named volumes are initialized to the contents of the image at that path, including all files and any directory permissions.
The latter point is a big one for me, it means you can create an initial default value for a data folder in your image, but update it using the container and keep those changes in a named volume. With bind mounts, if the directory is empty or doesn't exist, that's also what you get when you mount it in your container.
I was reading Project Atomic's guidance for images which states that the 2 main use cases for using a volume are:-
sharing data between containers
when writing large files to disk
I have neither of these use cases in my example using an Nginx image. I intended to mount a host directory as a volume in the path of the Nginx docroot in the container. This is so that I can push changes to a website's contents into the host rather then addressing the container. I feel it is easier to use this approach since I can - for example - just add my ssh key once to the host.
My question is, is this an appropriate use of a data volume and if not can anyone suggest an alternative approach to updating data inside a container?
One of the primary reasons for using Docker is to isolate your app from the server. This means you can run your container anywhere and get the same result. This is my main use case for it.
If you look at it from that point of view, having your container depend on files on the host machine for a deployed environment is counterproductive- running the same container on a different machine may result in different output.
If you do NOT care about that, and are just using docker to simplify the installation of nginx, then yes you can just use a volume from the host system.
Think about this though...
#Dockerfile
FROM nginx
ADD . /myfiles
#docker-compose.yml
web:
build: .
You could then use docker-machine to connect to your remote server and deploy a new version of your software with easy commands
docker-compose build
docker-compose up -d
even better, you could do
docker build -t me/myapp .
docker push me/myapp
and then deploy with
docker pull
docker run
There's a number of ways to achieve updating data in containers. Host volumes are a valid approach and probably the simplest way to achieve making your data available.
You can also copy files into and out of a container from the host. You may need to commit afterwards if you are stopping and removing the running web host container at all.
docker cp /src/www webserver:/www
You can copy files into a docker image build from your Dockerfile, which is the same process as above (copy and commit). Then restart the webserver container from the new image.
COPY /src/www /www
But I think the host volume is a good choice.
docker run -v /src/www:/www webserver command
Docker data containers are also an option for mounted volumes but they don't solve your immediate problem of copying data into your data container.
If you ever find yourself thinking "I need to ssh into this container", you are probably doing it wrong.
Not sure if I fully understand your request. But why you need do that to push files into Nginx container.
Manage volume in separate docker container, that's my suggestion and recommend by Docker.io
Data volumes
A data volume is a specially-designated directory within one or more containers that bypasses the Union File System. Data volumes provide several useful features for persistent or shared data:
Volumes are initialized when a container is created. If the container’s base image contains data at the specified mount point, that existing data is copied into the new volume upon volume initialization.
Data volumes can be shared and reused among containers.
Changes to a data volume are made directly.
Changes to a data volume will not be included when you update an image.
Data volumes persist even if the container itself is deleted.
refer: Manage data in containers
As said, one of the main reasons to use docker is to achieve always the same result. A best practice is to use a data only container.
With docker inspect <container_name> you can know the path of the volume on the host and update data manually, but this is not recommended;
or you can retrieve data from an external source, like a git repository