I'm currently playing with docker and wonders : how does that tech fits with things like chef/puppet/saltstack ( its conf part) ?
Is it going to make all those technologies pointless ?
The docker "philosophy" is that docker images should be simple, running only a single process. In that case chef-solo et al are often over-kill to create images. Docker mostly solves the "known state" problem, so there really isn't much that chef-solo gives you over running shell commands from your Dockerfile.
But sometimes it's convenient to create a single image that encapsulates everything, containing lots of moving parts. In that case, a provisioning tool could be very useful to put it together. You'll probably lose some of the 'layering' benefits of Docker, though.
I do find that provisioning tools are very helpful to put images onto a server and hooking them together. That's the central configuration store philosophy. Others are working on stuff like etcd for distributed configuration stores.
One common pattern is to use chef/puppet/salt/ansible to help you build the application stack inside the container, then seal the result into a standard Docker container. Once the build phase is over, it no longer matters which configuration management tool you used (if any), which makes your application more portable across infrastructure. See for example http://tech.paulcz.net/2013/09/creating-immutable-servers-wi...
- you can use configuration management tools to author Docker images; - you can use configuration management tools to deploy Docker (and start Docker containers).
The following presentation has some Puppet-specific information (but the concepts map neatly to other CM tools):
http://www.slideshare.net/jpetazzo/docker-and-puppet-puppet-...