To me a deployment of new code or config is a workflow. The ordering and timing of its progress of the fleet is very important. You want to be able to plan it,

To me a deployment of new code or config is a workflow. The ordering and timing of its progress of the fleet is very important. You want to be able to plan it, watch it, and pause or reverse it from that perspective. SSH is inadequate because this process should be much slower than the life of anyone's terminal window. You could approximate it with cronjob pulls if each node's schedule is a little offset from the previous. But you probably also want different rollout schedules available for different scenarios.