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System Design Masterclass · Security Architecture
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For decades, network security followed the castle-and-moat model: strong perimeter, trusted interior. Connect to the VPN, and you are "inside." Everything inside the network trusts everything else. The problem is that attackers who breach the perimeter get unrestricted lateral movement.
The 2020 SolarWinds attack demonstrated this catastrophically. Attackers gained access to one internal system and moved freely across government and corporate networks for months because internal traffic was implicitly trusted. They compromised 18,000 organizations including the US Treasury, Department of Homeland Security, and Microsoft.
Google pioneered the alternative after they were breached in Operation Aurora (2010). The Chinese government-backed attackers exploited a zero-day in Internet Explorer to gain a foothold inside Google's network, then moved laterally to access source code repositories and Gmail accounts of Chinese human rights activists. Google's response was radical: they eliminated the VPN entirely and built BeyondCorp. Every Google employee now accesses internal tools through the public internet, authenticated by device certificates, user identity, and context. Not by network location.
| Principle | What It Means | Implementation |
|---|---|---|
| Verify explicitly | Authenticate and authorize every request | mTLS between services, context-aware access proxies, continuous token validation |
| Least privilege access | Grant minimum permissions, just-in-time | RBAC + ABAC combined, time-bounded elevated access, automatic de-provisioning |
| Assume breach | Design as if attackers are already inside | Microsegmentation, east-west traffic inspection, encryption everywhere including internal networks |
Zero trust components:
| Component | Role | Products |
|---|---|---|
| Identity provider | Central source of truth for user and device identity | Okta, Azure AD, Google Workspace |
| Device trust | Verify device health, patch level, management status | CrowdStrike, Jamf, Intune |
| Policy engine | Evaluate access based on identity, device, context, risk | Google BeyondCorp, Cloudflare Access, Zscaler |
| Microsegmentation | Network segments per service, default deny-all | Illumio, VMware NSX, NetworkPolicy |
| Encryption | mTLS for all service-to-service, TLS for all client-to-server | Istio, Linkerd, cert-manager |
| Continuous monitoring | Real-time anomaly detection, session re-evaluation | CrowdStrike Falcon, Palo Alto Cortex |
Cloudflare Access processes over 1.4 trillion requests per day through its zero trust network. Google's BeyondCorp handles 4+ million internal access decisions daily. Netflix uses a similar model called LISA (Lemur Identity and Security Architecture) to protect access to its 700+ .