[agentgt]

Packer + Docker + custom cloud elastic stuff.

You can use docker compose and swarm but at some point you need to interface with how the cloud offering does elastic scaling (for example google has instance groups and deploy templates).

I haven't seen a good resource on this last part other than PaaS/IaaS doc itself. So I am curious as well.

There sort of needs to be a packer of deployment + composition but I suppose that is what chef and puppet are sort of for (I despise those tools).