You say:

systems/applications inside openstack instances using docker container

If you plan to run instances as Docker containers, you need to use the Nova Docker driver. I don't think it is still supported, though. Linux container instances (using LXD) are supported and are promoted by Canonical.

If you want to run Docker on instances, just deploy Docker on the instances. How? Any way you like; instances are just like physical machines as far as Docker is concerned. There are many options, but you can start at the Docker quick start series of web pages. Or use Magnum to deploy a Docker Swarm, Kubernetes or Mesos cluster on instances.