How can I backup a Docker-container with its data-volumes?

Question

I've been using this Docker-image tutum/wordpress to demonstrate a Wordpress website. Recently I found out that the image uses volumes for the MySQL-data.

So the problem is this: If I want to backup and restore the container I can try to commit an image, and then later delete the container, and create a new container from the committed image. But if I do that the volume gets deleted and all my data is gone.

There must be some simple way to backup my container plus its volume-data but I can't find it anywhere.

Answer 1

if I want to revert the container I can try to commit an image, and then later delete the container, and create a new container from the committed image. But if I do that the volume gets deleted and all my data is gone

As the docker user guide explains, data volumes are meant to persist data outside of a container filesystem. This also ease the sharing of data between multiple containers.

While Docker will never delete data in volumes (unless you delete the associated container with docker rm -v), volumes that are not referenced by any docker container are called dangling volumes. Those dangling volumes are difficult to get rid of and difficult to access.

This means that as soon as the last container using a volume is deleted, the data volume becomes dangling and its content difficult to access.

In order to prevent those dangling volumes, the trick is to create an additional docker container using the data volume you want to persist so that there will always be at least that docker container referencing the volume. This way you can delete the docker container running the wordpress app without losing the ease of access to that data volume content.

Such containers are called data volume containers.

There must be some simple way to back up my container plus volume data but I can't find it anywhere.

backup docker images

To backup docker images, use the docker save command that will produce a tar archive that can be used later on to create a new docker image with the docker load command.

backup docker containers

You can backup a docker container by different means

• by committing a new docker image based on the docker container current state using the docker commit command
• by exporting the docker container file system as a tar archive using the docker export command. You can later on create a new docker image from that tar archive with the docker import command.

Be aware that those commands will only backup the docker container layered file system. This excludes the data volumes.

backup docker data volumes

To backup a data volume you can run a new container using the volume you want to backup and executing the tar command to produce an archive of the volume content as described in the docker user guide.

In your particular case, the data volume is used to store the data for a MySQL server. So if you want to export a tar archive for this volume, you will need to stop the MySQL server first. To do so you will have to stop the wordpress container.

backup the MySQL data

An other way is to remotely connect to the MySQL server to produce a database dump with the mysqldump command. However in order for this to work, your MySQL server must be configured to accept remote connections and also have a user who is allowed to connect remotely. This might not be the case with the wordpress docker image you are using.

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Edit

Docker recently introduced Docker volume plugins which allow to delegate the handling of volumes to plugins implemented by vendors.

The docker run command has a new behavior for the -v option. It is now possible to pass it a volume name. Volumes created in that way are named and easy to reference later on, easing the issues with dangling volumes.

Edit 2

Docker introduced the docker volume prune command to delete all dangling volumes easily.

Answer 2

UPDATE 2

Raw single volume backup bash script:

#!/bin/bash # This script allows you to backup a single volume from a container # Data in given volume is saved in the current directory in a tar archive. CONTAINER_NAME=$1 VOLUME_NAME=$2  usage() {   echo "Usage: $0 [container name] [volume name]"   exit 1 }  if [ -z $CONTAINER_NAME ] then   echo "Error: missing container name parameter."   usage fi  if [ -z $VOLUME_NAME ] then   echo "Error: missing volume name parameter."   usage fi  sudo docker run --rm --volumes-from $CONTAINER_NAME -v $(pwd):/backup busybox tar cvf /backup/backup.tar $VOLUME_NAME 

Raw single volume restore bash script:

#!/bin/bash # This script allows you to restore a single volume from a container # Data in restored in volume with same backupped path NEW_CONTAINER_NAME=$1  usage() {   echo "Usage: $0 [container name]"   exit 1 }  if [ -z $NEW_CONTAINER_NAME ] then   echo "Error: missing container name parameter."   usage fi  sudo docker run --rm --volumes-from $NEW_CONTAINER_NAME -v $(pwd):/backup busybox tar xvf /backup/backup.tar 

Usage can be like this:

$ volume_backup.sh old_container /srv/www $ sudo docker stop old_container && sudo docker rm old_container $ sudo docker run -d --name new_container myrepo/new_container $ volume_restore.sh new_container 

Assumptions are: backup file is named backup.tar, it resides in the same directory as backup and restore script, volume name is the same between containers.

UPDATE

It seems to me that backupping volumes from containers is not different from backupping volumes from data containers.

Volumes are nothing else than paths linked to a container so the process is the same.

I don't know if docker-backup works also for same container volumes but you can use:

sudo docker run --rm --volumes-from yourcontainer -v $(pwd):/backup busybox tar cvf /backup/backup.tar /data 

and:

sudo docker run --rm --volumes-from yournewcontainer -v $(pwd):/backup busybox tar xvf /backup/backup.tar 

END UPDATE

There is this nice tool available which lets you backup and restore docker volumes containers:

https://github.com/discordianfish/docker-backup

if you have a container linked to some container volumes like this:

$ docker run --volumes-from=my-data-container --name my-server ... 

you can backup all the volumes like this:

$ docker-backup store my-server-backup.tar my-server 

and restore like this:

$ docker-backup restore my-server-backup.tar 

Or you can follow the official way:

How to port data-only volumes from one host to another?