Docker Tricks to Remember

This page was converted from my old blog and hasn't been reviewed. If you see an error please let me know in the comments.

Chances are if you have been working with docker for a while you may have noticed that removing containers does not free up the disk space associated with that container.  When removing the container the -v flag can be used to remove the volumes associated with that container.

[code language=”bash”]docker rm -v webapp[/code]

If it’s too late and you have a lot of orphaned containers you can use the docker-volume script to clean up your machine. https://github.com/cpuguy83/docker-volumes

Backing up Data in a Container

Backing up a docker volume may seem to be tricky since the data is buried on your filesystem.  But it’s actually easy to do by mapping a temporary container to your postgres volume and a local backup volume.

[code language=”bash”]

#Backup data in a volume
#remove it no need to keep it around.

$ docker run –rm –volumes-from dbdata -v $(pwd):/backup busybox tar cvf /backup/backup.tar /var/lib/postgresql/data

[/code]

Upgrading a container

Upgrading a container to a newer version can use a similar technique.  Stopping a container does not remove a volume.

[code language=”bash”]

$docker stop dbdata

$docker run –name newdbdata –volumes-from dbdata postgres:latest

$docker rm dbdata

[/code]

Accessing a shell in your container.

[code language=”bash”]

$docker excec -rm -ti web bash

[/code]