What it is
In AWS, a public subnet is one whose route table has a path to an internet gateway. In Azure, the same idea shows up as a subnet with a public IP, a load balancer, or a default route out.
Private means the resource cannot be reached from the open internet unless you build a door: a load balancer, a bastion, a VPN, or a private endpoint. Private is not “hidden if you do not tweet the IP.”
Databases, internal APIs, and admin consoles want private. Web front ends often need a controlled public door. The accident is putting the database on the same side of the door as the brochure site.
Why it matters in the meeting
When Selena says “it is in the VPC,” that is not an answer. VPCs and VNets contain both public and private space. Bart will ask which subnet, and whether it has a public IP “just for the demo.”
The meeting question is not “are we in the cloud.” It is “what can a stranger on the internet send a packet to.”
Real world
Most of the ugly screenshots start with a database, Redis cache, or Kubernetes API that was left with a public IP because the tutorial used one. The tutorial was not your threat model.
Private Link on AWS and Private Endpoints on Azure exist so traffic to storage and databases never needs a public address. If those still have public endpoints enabled “temporarily,” they are public.
Public means the internet can knock. Private means it cannot, unless you built a door and handed out a key. “It is in our network” is a sentence. “It has no public IP” is a fact.
What to ask
- Which production databases, caches, and admin endpoints still have a public IP?
- Is the default for new subnets private, or did we copy a tutorial that used public?
- Are S3 and Blob public access blocks on, or are we one bucket policy away from a press story?
- If we turned off every public IP tomorrow, what would actually break?
You just knew a little more Jack than you did five minutes ago.
All concepts