Also, when you are talking about container-based cluster deployment, the network (IP addresses, VPC, subnets etc) is useless for machine authentication, because

Also, when you are talking about container-based cluster deployment, the network (IP addresses, VPC, subnets etc) is useless for machine authentication, because any container in the cluster can run on any host machine at any time. As an example, Heroku is basically a giant compute cluster in a single security group (for each region). They used to publish the security group ids, so that you could whitelist inbound traffic from Heroku. Now they don't do that any more, which makes sense because really, what is the point of whitelisting all of Heroku? :-)