Private network vs public network: what is the difference, and how does it affect developer access?
Quick answer: a private network is only reachable from inside its own perimeter (on-site, or via VPN/Zero Trust); a public network — the open internet — is reachable from anywhere. Most real applications are a mix of both, and where you draw that line for each tier of a 3-tier app is what determines how developers actually get access to build and debug it.
The 3-tier shape
A classic 3-tier application has a presentation tier (the UI/web frontend), an application tier (the API/business logic), and a data tier (the database). The common — and correct — default is: presentation tier public (anyone can load the website), application tier reachable from the presentation tier and from trusted operators, and data tier private, reachable only from the application tier and nowhere else. The database should never be directly reachable from the public internet; every real breach story involving "someone left the database open" is this rule being skipped.
Where developer access gets awkward
Developers need to reach the application tier (to deploy, tail logs, run migrations) and sometimes the data tier (to debug a production issue) — tiers that are deliberately not public. Historically this is solved with a VPN: developers connect, get a private IP, and can now reach the app and data tiers directly. That works, but it means every developer's laptop becomes a trusted node with reach into production infrastructure, and every leaver, contractor rotation, or leaked credential is a live risk against that same reach. See What is a VPN, and why should you care? for why that model is under pressure.
The Zero Trust alternative
Rather than putting the developer's device on the private network, Zero Trust Access puts a policy in front of each specific private resource (a specific admin panel, a specific database console, a specific SSH host) and authenticates/authorises each request against identity — who you are, which group you're in, whether your device passes a posture check — without ever exposing that resource to the public internet or handing out network-level reach. A developer gets exactly the one thing they were granted, nothing else on the network is newly reachable, and access can be revoked per-resource in seconds rather than by rotating a shared VPN credential.
Practical takeaway
If your data tier is only reachable "because the VPN puts you on that subnet," that is broader access than almost anyone actually needs day to day — the access model, not just the network topology, is worth revisiting. It is also exactly the surface a Zero Trust/Access seat audit is designed to check for waste: seats retained after someone's access should have narrowed, not widened. There is a seat-audit waitlist open if that is a live question for your setup.