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Designing by zones

Before choosing services you have to draw boundaries. Network, trust and environment zones: the method that makes an architecture readable at a glance and protectable in parts.

Service line Cloud Architecture

Boundaries first, services second

An architecture diagram usually starts with the services: the database here, the application here, the queue there. The result is a map of parts with no edges, where you cannot see what is exposed, what is internal and what belongs to whom.

Designing by zones reverses the order: first you draw the boundaries and then you place each component inside the zone it belongs to. The question stops being 'which services do I use' and becomes 'what can talk to what, and through where'.

Three kinds of zone

Reference architecture by zonesInternet, exposed zone, application zone, data zone and a cross-cutting security and observability zone, with numbered flows.ARCHITECTURE · ZONESBoundaries firstINTERNET UsersEXPOSED ZONE Web firewall Load balancerAPPLICATION ZONE API gateway Services QueueDATA ZONE Database StoreSECURITY ANDOBSERVABILITY Identity Secrets Monitoring Logs12341 HTTPS from the internet · 2 filtered traffic to the load balancer and the API · 3 and 4 data access only from the applicationReference architecture; it does not correspond to any real caseN100F · n100f.com

Network zones. Where traffic can reach: what is exposed to the internet, what is internal, what is isolated. Every hop between zones goes through a controlled point.

Trust zones. What level of protection each part needs according to the data it handles. Personal or financial data lives in a more restricted zone than a public content service.

Environment zones. Development, testing and production genuinely separated, with no shortcuts between them.

Rules of the method

  1. Each component lives in a single zone. If it seems to be in two, it is two components.
  2. Flows between zones are numbered and described: who initiates, over which port or protocol and with what authentication.
  3. Zones are distinguished by colour, consistently across every diagram in the organisation. The reader learns to read them once.
  4. The security and observability zone is cross-cutting: logging, monitoring and identity management reach all the others.
  5. What is pending is drawn differently (with a dashed line, for instance), so the diagram tells the truth about what exists and what does not.

Why it works

A zone diagram answers at a glance the questions that matter in a review: what is exposed, where the sensitive data is, what happens if a zone goes down and what has to be protected first. And because zones are stable, the diagram survives changes of service: you swap a part inside a zone without redrawing everything.

How we apply it: Cloud Architecture.

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