Fortress in the Cloud

By Lee Atchison · April 16, 2025 · Best Practices, Cloud Adoption, Security

Fortress in the Cloud

As modern applications grow more complex and valuable, their security becomes increasingly critical. Yet many organizations still operate with a flat security model—one breach and attackers gain access to everything. This approach is like building a house with a reinforced front door but paper-thin walls. How can you improve your application security to reduce your risk of attack? Use isolation zones. Isolation zones aren’t just a best practice—it’s the difference between a minor security incident and a catastrophic breach that makes headlines.

How Do You Use Security Zones?

When creating the production operational backend infrastructure for a modern application, it’s generally considered best practice for security purposes to split the application infrastructure into multiple security zones. This is so that a security breach in one area can still be limited to impact only the resources within that one zone. Done correctly, this can take a security breach that might otherwise be a massive impact on your application integrity and turn it into a much smaller, perhaps insignificant breach that has minimal impact.

There are many ways to architect your security zones, but a typical model involves three standard zones. In this model, the three zones are called the public zone, the private zone, and the DMZ.

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The three zones have the following purposes:

Public zone. This is the zone that is connected directly to the internet. It’s exposed to traffic coming from the internet and, as such, is the least secure zone and the most vulnerable zone to compromises. The only services that exist in this zone are the services that absolutely must be connected directly to the internet to give access to your application. Examples include API Gateways, traffic managers, firewalls, load balancers, and similar services.
Private zone. This is the zone where the vast majority of your backend application exists. All of your data is stored in databases maintained in the private zone, and the majority of your application services operate in this zone. As a result, it’s considered the safest zone and is the hardest to breach from a security standpoint.
Demilitarized Zone (DMZ). The DMZ is the zone between the public zone and the private zone. This zone is intended to act as a shield or security layer between the two zones. All communications between the relatively insecure services in the public zone and the relatively secure services in the private zone must go through a service in the DMZ. These “go-between” services provide a high level of security protection and reduce the likelihood of compromises to the sensitive private zone services from highly vulnerable public zone services. In the cloud, these zones are constructed using multiple virtual private clouds (VPCs), which are essentially separate networking segments that have specific network and application-level security provisions attached. The cloud provider gives you tools to control the security aspects of each zone. Traffic is limited between zones to improve security by using Network Access Controls (NACLs), Security Groups (SGs), and software and hardware firewalls. Security within each zone may be different. For instance, in the public zone, it may be reasonable to allow services inside this lower-secure zone to cross-talk in a very open manner. However, in the private zone, communications between services may be highly restricted, and only communications required for the application to function and be supported may be allowed. The exact details of how each zone is configured varies, depending on the security needs of the application and the security policies of the company.

Keep Resilient, Keep Secure

Security isolation isn’t just another checkbox on your compliance list—it’s a fundamental architectural decision that shapes your application’s resilience. Throughout my career, I’ve seen it over and over again. A proper zone implementation saves organizations from potentially devastating breaches. When attackers breach the public zone, they find themselves stranded, unable to reach the crown jewels in the private zone.

Remember, in today’s threat landscape, it’s not a question of if you’ll face an attack, but when. By implementing the three-zone model I’ve outlined—public zone, DMZ, and private zone—you’re not just following best practices; you’re building multiple layers of defense that transform potential disasters into manageable incidents.

Your future self (and your security team) will thank you.