To integrate Docker with OpenStack, a compute node's driver needs to be changed from libvirt to docker. This forces an entire compute node's worth of virtualization capacity to be converted to container capacity. Docker containers and virtual machines cannot coexist on a compute node together. Docker containers and virtual machines can coexist in the same OpenStack cluster as long as there are at least two compute nodes, one for containers and one for virtual machines. For now, you will convert your existing compute node to docker, then in Chapter 11, Scaling Horizontally, you will attach another compute node to re-enable virtual machine management.