2014-05-21 17:05:19 -04:00
|
|
|
page_title: Managing Data in Containers
|
|
|
|
page_description: How to manage data inside your Docker containers.
|
|
|
|
page_keywords: Examples, Usage, volume, docker, documentation, user guide, data, volumes
|
|
|
|
|
|
|
|
# Managing Data in Containers
|
|
|
|
|
2014-06-16 03:52:23 -04:00
|
|
|
So far we've been introduced to some [basic Docker
|
2014-05-21 17:05:19 -04:00
|
|
|
concepts](/userguide/usingdocker/), seen how to work with [Docker
|
|
|
|
images](/userguide/dockerimages/) as well as learned about [networking
|
|
|
|
and links between containers](/userguide/dockerlinks/). In this section
|
|
|
|
we're going to discuss how you can manage data inside and between your
|
|
|
|
Docker containers.
|
|
|
|
|
|
|
|
We're going to look at the two primary ways you can manage data in
|
|
|
|
Docker.
|
|
|
|
|
|
|
|
* Data volumes, and
|
|
|
|
* Data volume containers.
|
|
|
|
|
|
|
|
## Data volumes
|
|
|
|
|
|
|
|
A *data volume* is a specially-designated directory within one or more
|
|
|
|
containers that bypasses the [*Union File
|
|
|
|
System*](/terms/layer/#ufs-def) to provide several useful features for
|
|
|
|
persistent or shared data:
|
|
|
|
|
|
|
|
- Data volumes can be shared and reused between containers
|
|
|
|
- Changes to a data volume are made directly
|
|
|
|
- Changes to a data volume will not be included when you update an image
|
|
|
|
- Volumes persist until no containers use them
|
|
|
|
|
|
|
|
### Adding a data volume
|
|
|
|
|
|
|
|
You can add a data volume to a container using the `-v` flag with the
|
|
|
|
`docker run` command. You can use the `-v` multiple times in a single
|
|
|
|
`docker run` to mount multiple data volumes. Let's mount a single volume
|
|
|
|
now in our web application container.
|
|
|
|
|
|
|
|
$ sudo docker run -d -P --name web -v /webapp training/webapp python app.py
|
|
|
|
|
|
|
|
This will create a new volume inside a container at `/webapp`.
|
|
|
|
|
|
|
|
> **Note:**
|
|
|
|
> You can also use the `VOLUME` instruction in a `Dockerfile` to add one or
|
|
|
|
> more new volumes to any container created from that image.
|
|
|
|
|
|
|
|
### Mount a Host Directory as a Data Volume
|
|
|
|
|
|
|
|
In addition to creating a volume using the `-v` flag you can also mount a
|
|
|
|
directory from your own host into a container.
|
|
|
|
|
|
|
|
$ sudo docker run -d -P --name web -v /src/webapp:/opt/webapp training/webapp python app.py
|
|
|
|
|
|
|
|
This will mount the local directory, `/src/webapp`, into the container as the
|
|
|
|
`/opt/webapp` directory. This is very useful for testing, for example we can
|
|
|
|
mount our source code inside the container and see our application at work as
|
|
|
|
we change the source code. The directory on the host must be specified as an
|
|
|
|
absolute path and if the directory doesn't exist Docker will automatically
|
|
|
|
create it for you.
|
|
|
|
|
2014-06-08 14:31:10 -04:00
|
|
|
> **Note:**
|
2014-07-20 20:05:37 -04:00
|
|
|
> This is not available from a `Dockerfile` due to the portability
|
2014-05-21 17:05:19 -04:00
|
|
|
> and sharing purpose of it. As the host directory is, by its nature,
|
2014-07-20 20:05:37 -04:00
|
|
|
> host-dependent, a host directory specified in a `Dockerfile` probably
|
|
|
|
> wouldn't work on all hosts.
|
2014-05-21 17:05:19 -04:00
|
|
|
|
|
|
|
Docker defaults to a read-write volume but we can also mount a directory
|
|
|
|
read-only.
|
|
|
|
|
|
|
|
$ sudo docker run -d -P --name web -v /src/webapp:/opt/webapp:ro training/webapp python app.py
|
|
|
|
|
|
|
|
Here we've mounted the same `/src/webapp` directory but we've added the `ro`
|
|
|
|
option to specify that the mount should be read-only.
|
|
|
|
|
2014-07-04 13:52:10 -04:00
|
|
|
### Mount a Host File as a Data Volume
|
|
|
|
|
2014-07-09 03:21:31 -04:00
|
|
|
The `-v` flag can also be used to mount a single file - instead of *just*
|
|
|
|
directories - from the host machine.
|
2014-07-04 13:52:10 -04:00
|
|
|
|
|
|
|
$ sudo docker run --rm -it -v ~/.bash_history:/.bash_history ubuntu /bin/bash
|
|
|
|
|
2014-07-07 07:01:04 -04:00
|
|
|
This will drop you into a bash shell in a new container, you will have your bash
|
2014-07-09 03:21:31 -04:00
|
|
|
history from the host and when you exit the container, the host will have the
|
2014-07-07 07:01:04 -04:00
|
|
|
history of the commands typed while in the container.
|
2014-07-04 13:52:10 -04:00
|
|
|
|
|
|
|
> **Note:**
|
2014-07-07 07:01:04 -04:00
|
|
|
> Many tools used to edit files including `vi` and `sed --in-place` may result
|
2014-07-09 03:21:31 -04:00
|
|
|
> in an inode change. Since Docker v1.1.0, this will produce an error such as
|
2014-07-07 07:01:04 -04:00
|
|
|
> "*sed: cannot rename ./sedKdJ9Dy: Device or resource busy*". In the case where
|
|
|
|
> you want to edit the mounted file, it is often easiest to instead mount the
|
|
|
|
> parent directory.
|
2014-07-04 13:52:10 -04:00
|
|
|
|
2014-05-21 17:05:19 -04:00
|
|
|
## Creating and mounting a Data Volume Container
|
|
|
|
|
|
|
|
If you have some persistent data that you want to share between
|
|
|
|
containers, or want to use from non-persistent containers, it's best to
|
|
|
|
create a named Data Volume Container, and then to mount the data from
|
|
|
|
it.
|
|
|
|
|
|
|
|
Let's create a new named container with a volume to share.
|
|
|
|
|
2014-07-15 09:32:44 -04:00
|
|
|
$ sudo docker run -d -v /dbdata --name dbdata training/postgres echo Data-only container for postgres
|
2014-05-21 17:05:19 -04:00
|
|
|
|
|
|
|
You can then use the `--volumes-from` flag to mount the `/dbdata` volume in another container.
|
|
|
|
|
2014-06-24 05:24:45 -04:00
|
|
|
$ sudo docker run -d --volumes-from dbdata --name db1 training/postgres
|
2014-05-21 17:05:19 -04:00
|
|
|
|
|
|
|
And another:
|
|
|
|
|
2014-06-24 05:24:45 -04:00
|
|
|
$ sudo docker run -d --volumes-from dbdata --name db2 training/postgres
|
2014-05-21 17:05:19 -04:00
|
|
|
|
2014-06-23 11:08:34 -04:00
|
|
|
You can use multiple `--volumes-from` parameters to bring together multiple data
|
2014-05-21 17:05:19 -04:00
|
|
|
volumes from multiple containers.
|
|
|
|
|
|
|
|
You can also extend the chain by mounting the volume that came from the
|
|
|
|
`dbdata` container in yet another container via the `db1` or `db2` containers.
|
|
|
|
|
2014-06-24 05:24:45 -04:00
|
|
|
$ sudo docker run -d --name db3 --volumes-from db1 training/postgres
|
2014-05-21 17:05:19 -04:00
|
|
|
|
|
|
|
If you remove containers that mount volumes, including the initial `dbdata`
|
|
|
|
container, or the subsequent containers `db1` and `db2`, the volumes will not
|
|
|
|
be deleted until there are no containers still referencing those volumes. This
|
|
|
|
allows you to upgrade, or effectively migrate data volumes between containers.
|
|
|
|
|
|
|
|
## Backup, restore, or migrate data volumes
|
|
|
|
|
|
|
|
Another useful function we can perform with volumes is use them for
|
|
|
|
backups, restores or migrations. We do this by using the
|
|
|
|
`--volumes-from` flag to create a new container that mounts that volume,
|
|
|
|
like so:
|
|
|
|
|
|
|
|
$ sudo docker run --volumes-from dbdata -v $(pwd):/backup ubuntu tar cvf /backup/backup.tar /dbdata
|
|
|
|
|
2014-07-28 16:39:17 -04:00
|
|
|
Here we've launched a new container and mounted the volume from the
|
2014-05-21 17:05:19 -04:00
|
|
|
`dbdata` container. We've then mounted a local host directory as
|
|
|
|
`/backup`. Finally, we've passed a command that uses `tar` to backup the
|
|
|
|
contents of the `dbdata` volume to a `backup.tar` file inside our
|
|
|
|
`/backup` directory. When the command completes and the container stops
|
|
|
|
we'll be left with a backup of our `dbdata` volume.
|
|
|
|
|
2014-07-25 03:06:38 -04:00
|
|
|
You could then restore it to the same container, or another that you've made
|
2014-05-21 17:05:19 -04:00
|
|
|
elsewhere. Create a new container.
|
|
|
|
|
2014-06-25 01:53:59 -04:00
|
|
|
$ sudo docker run -v /dbdata --name dbdata2 ubuntu /bin/bash
|
2014-05-21 17:05:19 -04:00
|
|
|
|
|
|
|
Then un-tar the backup file in the new container's data volume.
|
|
|
|
|
|
|
|
$ sudo docker run --volumes-from dbdata2 -v $(pwd):/backup busybox tar xvf /backup/backup.tar
|
|
|
|
|
|
|
|
You can use this techniques above to automate backup, migration and
|
|
|
|
restore testing using your preferred tools.
|
|
|
|
|
|
|
|
# Next steps
|
|
|
|
|
|
|
|
Now we've learned a bit more about how to use Docker we're going to see how to
|
|
|
|
combine Docker with the services available on
|
2014-06-01 16:48:04 -04:00
|
|
|
[Docker Hub](https://hub.docker.com) including Automated Builds and private
|
2014-05-21 17:05:19 -04:00
|
|
|
repositories.
|
|
|
|
|
2014-06-01 16:48:04 -04:00
|
|
|
Go to [Working with Docker Hub](/userguide/dockerrepos).
|
2014-05-21 17:05:19 -04:00
|
|
|
|