$ docker service create \
--mount 'type=volume,src=<VOLUME-NAME>,dst=<CONTAINER-PATH>,volume-driver=local,volume-opt=type=nfs,volume-opt=device=<nfs-server>:<nfs-path>,"volume-opt=o=addr=<nfs-address>,vers=4,soft,timeo=180,bg,tcp,rw"'
--name myservice \
<IMAGE>
The examples below show both the --mount and -v syntax where possible, with
--mount first.
Differences between -v and --mount behavior
As opposed to bind mounts, all options for volumes are available for both
--mount and -v flags.
Volumes used with services, only support --mount.
Create and manage volumes
Unlike a bind mount, you can create and manage volumes outside the scope of any
container.
Create a volume:
$ docker volume create my-vol
List volumes:
$ docker volume ls
local my-vol
Inspect a volume:
$ docker volume inspect my-vol
"Driver": "local",
"Labels": {},
"Mountpoint": "/var/lib/docker/volumes/my-vol/_data",
"Name": "my-vol",
"Options": {},
"Scope": "local"
Remove a volume:
$ docker volume rm my-vol
Start a container with a volume
If you start a container with a volume that doesn’t yet exist, Docker creates
the volume for you. The following example mounts the volume myvol2 into
/app/ in the container.
The -v and --mount examples below produce the same result. You can’t run
them both unless you remove the devtest container and the myvol2 volume
after running the first one.
--mount
Use docker inspect devtest to verify that Docker created the volume and it mounted
correctly. Look for the Mounts section:
"Mounts": [
"Type": "volume",
"Name": "myvol2",
"Source": "/var/lib/docker/volumes/myvol2/_data",
"Destination": "/app",
"Driver": "local",
"Mode": "",
"RW": true,
"Propagation": ""
This shows that the mount is a volume, it shows the correct source and
destination, and that the mount is read-write.
Stop the container and remove the volume. Note volume removal is a separate
step.
$ docker container stop devtest
$ docker container rm devtest
$ docker volume rm myvol2
Use a volume with Docker Compose
The example below shows a single Docker Compose service with a volume:
services:
frontend:
image: node:lts
volumes:
- myapp:/home/node/app
volumes:
myapp:
Running docker compose up for the first time creates a volume. Docker reuses the same volume when you run the command subsequently.
You can create a volume directly outside of Compose using docker volume create and
then reference it inside docker-compose.yml as follows:
services:
frontend:
image: node:lts
volumes:
- myapp:/home/node/app
volumes:
myapp:
external: true
For more information about using volumes with Compose, refer to the
Volumes
section in the Compose specification.
Start a service with volumes
When you start a service and define a volume, each service container uses its own
local volume. None of the containers can share this data if you use the local
volume driver. However, some volume drivers do support shared storage.
The following example starts an nginx service with four replicas, each of which
uses a local volume called myvol2.
$ docker service create -d \
--replicas=4 \
--name devtest-service \
--mount source=myvol2,target=/app \
nginx:latest
Use docker service ps devtest-service to verify that the service is running:
$ docker service ps devtest-service
ID NAME IMAGE NODE DESIRED STATE CURRENT STATE ERROR PORTS
4d7oz1j85wwn devtest-service.1 nginx:latest moby Running Running 14 seconds ago
You can remove the service to stop the running tasks:
$ docker service rm devtest-service
Removing the service doesn’t remove any volumes created by the service.
Volume removal is a separate step.
Syntax differences for services
The docker service create command doesn’t support the -v or --volume flag.
When mounting a volume into a service’s containers, you must use the --mount
flag.
Populate a volume using a container
If you start a container which creates a new volume, and the container
has files or directories in the directory to be mounted such as /app/,
Docker copies the directory’s contents into the volume. The container then
mounts and uses the volume, and other containers which use the volume also
have access to the pre-populated content.
To show this, the following example starts an nginx container and
populates the new volume nginx-vol with the contents of the container’s
/usr/share/nginx/html directory. This is where Nginx stores its default HTML
content.
The --mount and -v examples have the same end result.
--mount
$
docker run -d \
--name=nginxtest \
--mount source=nginx-vol,destination=/usr/share/nginx/html \
nginx:latest
After running either of these examples, run the following commands to clean up
the containers and volumes. Note volume removal is a separate step.
$ docker container stop nginxtest
$ docker container rm nginxtest
$ docker volume rm nginx-vol
Use a read-only volume
For some development applications, the container needs to write into the bind
mount so that changes are propagated back to the Docker host. At other times,
the container only needs read access to the data. Multiple
containers can mount the same volume. You can simultaneously mount a
single volume as read-write for some containers and as read-only for others.
The following example changes the one above. It mounts the directory as a read-only
volume, by adding ro to the (empty by default) list of options, after the
mount point within the container. Where multiple options are present, you can separate
them using commas.
The --mount and -v examples have the same result.
--mount
$ docker run -d \
--name=nginxtest \
--mount source=nginx-vol,destination=/usr/share/nginx/html,readonly \
nginx:latest
Use docker inspect nginxtest to verify that Docker created the read-only mount
correctly. Look for the Mounts section:
"Mounts": [
"Type": "volume",
"Name": "nginx-vol",
"Source": "/var/lib/docker/volumes/nginx-vol/_data",
"Destination": "/usr/share/nginx/html",
"Driver": "local",
"Mode": "",
"RW": false,
"Propagation": ""
Stop and remove the container, and remove the volume. Volume removal is a
separate step.
$ docker container stop nginxtest
$ docker container rm nginxtest
$ docker volume rm nginx-vol
Share data between machines
When building fault-tolerant applications, you may need to configure multiple
replicas of the same service to have access to the same files.
There are several ways to achieve this when developing your applications.
One is to add logic to your application to store files on a cloud object
storage system like Amazon S3. Another is to create volumes with a driver that
supports writing files to an external storage system like NFS or Amazon S3.
Volume drivers allow you to abstract the underlying storage system from the
application logic. For example, if your services use a volume with an NFS
driver, you can update the services to use a different driver. For example, to
store data in the cloud, without changing the application logic.
Use a volume driver
When you create a volume using docker volume create, or when you start a
container which uses a not-yet-created volume, you can specify a volume driver.
The following examples use the vieux/sshfs volume driver, first when creating
a standalone volume, and then when starting a container which creates a new
volume.
Initial setup
The following example assumes that you have two nodes, the first of which is a Docker
host and can connect to the second node using SSH.
On the Docker host, install the vieux/sshfs plugin:
$ docker plugin install --grant-all-permissions vieux/sshfs
Create a volume using a volume driver
This example specifies an SSH password, but if the two hosts have shared keys
configured, you can exclude the password. Each volume driver may have zero or more
configurable options, you specify each of them using an -o flag.
$ docker volume create --driver vieux/sshfs \
-o sshcmd=test@node2:/home/test \
-o password=testpassword \
sshvolume
Start a container which creates a volume using a volume driver
The following example specifies an SSH password. However, if the two hosts have
shared keys configured, you can exclude the password.
Each volume driver may have zero or more configurable options.
Note:
If the volume driver requires you to pass any options,
you must use the --mount flag to mount the volume, and not -v.
$ docker run -d \
--name sshfs-container \
--volume-driver vieux/sshfs \
--mount src=sshvolume,target=/app,volume-opt=sshcmd=test@node2:/home/test,volume-opt=password=testpassword \
nginx:latest
Create a service which creates an NFS volume
The following example shows how you can create an NFS volume when creating a service.
It uses 10.0.0.10 as the NFS server and /var/docker-nfs as the exported directory on the NFS server.
Note that the volume driver specified is local.
NFSv3
$ docker service create -d \
--name nfs-service \
--mount 'type=volume,source=nfsvolume,target=/app,volume-driver=local,volume-opt=type=nfs,volume-opt=device=:/var/docker-nfs,volume-opt=o=addr=10.0.0.10' \
nginx:latest
NFSv4
$ docker service create -d \
--name nfs-service \
--mount 'type=volume,source=nfsvolume,target=/app,volume-driver=local,volume-opt=type=nfs,volume-opt=device=:/var/docker-nfs,"volume-opt=o=addr=10.0.0.10,rw,nfsvers=4,async"' \
nginx:latest
Create CIFS/Samba volumes
You can mount a Samba share directly in Docker without configuring a mount point on your host.
$ docker volume create \
--driver local \
--opt type=cifs \
--opt device=//uxxxxx.your-server.de/backup \
--opt o=addr=uxxxxx.your-server.de,username=uxxxxxxx,password=*****,file_mode=0777,dir_mode=0777 \
--name cif-volume
The addr option is required if you specify a hostname instead of an IP.
This lets Docker perform the hostname lookup.
Block storage devices
You can mount a block storage device, such as an external drive or a drive partition, to a container.
The following example shows how to create and use a file as a block storage device,
and how to mount the block device as a container volume.
Important
The following procedure is only an example.
The solution illustrated here isn’t recommended as a general practice.
Don’t attempt this approach unless you’re confident about what you’re doing.
How mounting block devices works
Under the hood, the --mount flag using the local storage driver invokes the
Linux mount syscall and forwards the options you pass to it unaltered.
Docker doesn’t implement any additional functionality on top of the native mount features supported by the Linux kernel.
If you’re familiar with the
Linux mount command,
you can think of the --mount options as forwarded to the mount command in the following manner:
$ mount -t <mount.volume-opt.type> <mount.volume-opt.device> <mount.dst> -o <mount.volume-opts.o>
To explain this further, consider the following mount command example.
This command mounts the /dev/loop5 device to the path /external-drive on the system.
$ mount -t ext4 /dev/loop5 /external-drive
The following docker run command achieves a similar result, from the point of view of the container being run.
Running a container with this --mount option sets up the mount in the same way as if you had executed the
mount command from the previous example.
$ docker run \
--mount='type=volume,dst=/external-drive,volume-driver=local,volume-opt=device=/dev/loop5,volume-opt=type=ext4'
You can’t run the mount command inside the container directly,
because the container is unable to access the /dev/loop5 device.
That’s why the docker run command uses the --mount option.
Example: Mounting a block device in a container
The following steps create an ext4 filesystem and mounts it into a container.
The filesystem support of your system depends on the version of the Linux kernel you are using.
Create a file and allocate some space to it:
$ fallocate -f 1G disk.raw
Build a filesystem onto the disk.raw file:
$ mkfs.ext4 disk.raw
Create a loop device:
$ losetup -f --show disk.raw
/dev/loop5
losetup creates an ephemeral loop device that’s removed after
system reboot, or manually removed with losetup -d.
Run a container that mounts the loop device as a volume:
$ docker run -it --rm \
--mount='type=volume,dst=/external-drive,volume-driver=local,volume-opt=device=/dev/loop5,volume-opt=type=ext4' \
ubuntu bash
When the container starts, the path /external-drive mounts the
disk.raw file from the host filesystem as a block device.
When you’re done, and the device is unmounted from the container,
detach the loop device to remove the device from the host system:
$ losetup -d /dev/loop5
Back up, restore, or migrate data volumes
Volumes are useful for backups, restores, and migrations.
Use the --volumes-from flag to create a new container that mounts that volume.
Back up a volume
For example, create a new container named dbstore:
$ docker run -v /dbdata --name dbstore ubuntu /bin/bash
In the next command:
Launch a new container and mount the volume from the dbstore container
Mount a local host directory as /backup
Pass a command that tars the contents of the dbdata volume to a backup.tar file inside our /backup directory.
$ docker run --rm --volumes-from dbstore -v $(pwd):/backup ubuntu tar cvf /backup/backup.tar /dbdata
When the command completes and the container stops, it creates a backup of
the dbdata volume.
Restore volume from a backup
With the backup just created, you can restore it to the same container,
or to another container that you created elsewhere.
For example, create a new container named dbstore2:
$ docker run -v /dbdata --name dbstore2 ubuntu /bin/bash
Then, un-tar the backup file in the new container’s data volume:
$ docker run --rm --volumes-from dbstore2 -v $(pwd):/backup ubuntu bash -c "cd /dbdata && tar xvf /backup/backup.tar --strip 1"
You can use the techniques above to automate backup, migration, and restore
testing using your preferred tools.
Remove volumes
A Docker data volume persists after you delete a container. There are two types
of volumes to consider:
Named volumes have a specific source from outside the container, for example, awesome:/bar.
Anonymous volumes have no specific source. Therefore, when the container is deleted, you can instruct the Docker Engine daemon to remove them.
Remove anonymous volumes
To automatically remove anonymous volumes, use the --rm option. For example,
this command creates an anonymous /foo volume. When you remove the container,
the Docker Engine removes the /foo volume but not the awesome volume.
$ docker run --rm -v /foo -v awesome:/bar busybox top
Note:
If another container binds the volumes with
--volumes-from, the volume definitions are copied and the
anonymous volume also stays after the first container is removed.
Remove all volumes
To remove all unused volumes and free up space:
