Backup a running Docker container?

Question

Is it possible to backup a running Docker container? Is the export command suitable for doing that?

Answer 1

Posted by one friend in comments

Hi Slava, sorry that your question was closed. For the record, Slava is talking about docker.io, a runtime for linux containers. Yes, docker export is a suitable approach. It will generate a tarball of your entire container filesystem state, and dump it on stdout. So

docker export $CONTAINER_ID > $CONTAINER_ID-backup.tar

will yield a usable tarball. You can re-import the tarball with

docker import - slava/$CONTAINER_ID-backup < $CONTAINER_ID-backup.tar

Note the original metadata (eg id of the original image) will be lost. This should be fixed in future versions of docker. – Solomon Hykes Apr 2 '13 at 6:35

Adding here so one can find from summary that question was answered. Thanks Solomon!

Answer 2

export has some limitations: it won't export the data volume.

Here's data volume means:

1. There's a VOLUME defined in the image's Dockerfile.
2. The container is start with a parameter like this: -v /webapp

More about data: https://docs.docker.com/userguide/dockervolumes/

The way to handle this situation is start a new container with '--volumes-from' parameter to hook on that container, so you can visit the data volume.

Examples:

1. Visit the data: (in a bash)

docker run -it --volumes-from target_container ubuntu bash

2. Backup to host: (a postgres container)

docker run -it --volumes-from some_postgres -v /host/path:/container/path --rm ubuntu bash -c "tar -cvf /container/path/postgres-backup.tar /var/lib/postgresql/data"