This will build a docker image that runs BitTorrent Sync.

docker build -t btsync .

docker run -d --name mybtsync -p 55555:55555 -e SECRET=ANL7... -v /btsync/ btsync

where ANL7... is the secret. If you don't specify a secret, one will be created for you and the container will immediately exit.

55555 is the btsync listening port we use. If you do not explicitly set a public port, a random open port will be used because the ports are exposed in the Dockerfile

-v mount a local directory in the container [host-dir]:[container-dir]. If you leave of the host-dir, a random place will be used.

To have another container use this volume:

docker run -i -t --volumes-from mybtsync busybox /bin/ls /btsync

If you have another host running btsync with a known IP and port, you can specify it using -e HOST=192.168.59.3:12345, for faster discovery.

More details are available in this tutorial.