What happens when the docker host restarts?

Question

What happens when the docker host is shut down and restarted?

• will the images that were running be restarted?
• will the changes that were made to those images persist, or will a new instance of the image be spawned and changes be lost?
• does docker have any configuration option, such as the list of images to be automatically executed at startup and the options to run the images? Where? If not, I suppose only the docker command line can be used to alter docker state. Where is that state stored (I suppose somewhere in /var). This could be useful to backup the docker state.

(I'd have liked to find this in the FAQ)

Answer 1

will the images that were running be restarted?

Docker will restart containers when the daemon restarts if you pass -r=True to the startup options. On Ubuntu, you can accomplish this permanently by modifying DOCKER_OPTS="-r=true" in /etc/default/docker.

will the changes that were made to those images persist, or will a new instance of the image be spawned and changes be lost?

Containers will be stopped. Any modifications to the container will still be present when the container next starts, which will happen automatically when the docker daemon starts if -r=true is provided as mentioned above.

where is the docker configuration stored on the host system?

There is no configuration file per se. You can tune the upstart/init options in /etc/default/docker.