Infrastructure, described as a code, containing VM templates, scaling mechanisms, provision scripts, deployment scripts can be as ephemeral as a source code storage.
Ephemerity metric (EM) can be a minimun number of core nodes that are required for infrastructure to be functional
My assumtion that minimal level of ephemerity is 2:
1st is a node that stores sources
2nd is a node that actuates the code
all other nodes can be ephemeral, spawned by actuator, even cloud hosting it self, assuming that actuator have access to needed resources.
At the moment typical infrastructure have much higher EM - node for source code, node for jenkins, node for cloud orchestrator, node for database, node for monitoring, node for mail server, third-party nodes, network gates are all non-ephemeric
Might be a point of study also the dependency between EM and security/perfomance/reliability