First, run a Redis instance on your machine. It will automatically expose the /data volume.
docker run --name my-forum-redis -d -p 6379:6379 nodebb/docker:centos-redis
Next, launch the NodeBB instance from this repository, so it links with the just-launched Redis instance.
docker run --name dockerdev-nodebb --link dockerdev-redis:redis -P -t -i nodebb/docker:centos
You will be asked to configure your NodeBB instance, as no config file was found. Simply press enter for all settings except Redis hostname, which should be redis as it is linked using the --linked parameter to our Redis instance, and the administrator username, e-mail and password. The default port of nodebb, and ports 80 and 443 have been exposed for your convenienc. You can keep the default nodebb port or change it.
NodeBB will launch the setup and automatically close. Next, simply start the instance again. It will this time find a config file and start as a daemon.
docker start my-forum-nodebb
Your NodeBB instance will be accessible on port 4567. Check docker ps for more details.
Simply use the /data volume inside your Redis instance. See the official guide on making backups.