Amazon Web Services (AWS) offers a range of foundational tools that power much of the internet. If you’ve built high-throughput applications in the AWS ecosystem, chances are you’ve encountered AWS Network Load Balancer (NLB). NLBs operate at Layer 4 of the OSI model and are designed for low-latency forwarding of TCP, UDP, and TLS traffic. They support features such as static IPs, long-lived connections, and flexible configuration options.
NLBs are widely used in scenarios requiring consistent performance—such as serving as front-ends for latency-sensitive database queries or full backend services. While Application Load Balancers (ALBs) operate at a higher layer and offer deep inspection of HTTP traffic, NLBs remain the tool of choice for high-throughput, low-complexity requirements.
Understanding Zero Trust Architecture (ZTA)
Zero Trust Architecture is based on the principle of “never trust, always verify.” Initially conceptualized in 2010, it has gained prominence with the growing adoption of cloud infrastructure. Traditional security models assume that anything within a network boundary is trustworthy. However, in distributed cloud environments, such assumptions no longer hold true.
Zero Trust eliminates implicit trust. Every device, user, or service must authenticate and authorize explicitly before being granted access—aligning with the principle of least privilege and continuous verification.
Why Zero Trust Matters for AWS NLBs
AWS NLBs often act as the entry point to your architecture, processing traffic from the internet, other AWS services, or across accounts. This makes them a prime candidate for enforcing Zero Trust policies:
- NLBs as Gateways: Similar to a front door in a home, NLBs regulate who or what gains access. Without restrictions, unauthorized entities can gain entry.
- Layer 4 Simplicity: While this enhances performance, it limits visibility into application-layer data. Zero Trust compensates for this by emphasizing TLS, identity-aware proxies, and traffic filtering.
- High-Value Traffic: NLBs commonly serve business-critical applications like financial platforms, gaming systems, and streaming services—demanding robust yet efficient security.
- Fuzzy Network Boundaries: Many NLBs are integrated within PrivateLink or multi-account environments. The origin of traffic cannot be inherently trusted, even when internal to AWS. Zero Trust mandates that all access be scrutinized.
Core Zero Trust Principles Applied to NLBs
1. Never Trust, Always Verify
Though NLBs can’t inspect packet payloads, they support TLS termination with certificates from AWS Certificate Manager. Additional authentication layers (e.g., OAuth or IAM) can be applied at downstream services to ensure every connection is authenticated.
2. Least Privilege Access
Over-permissive access, such as wide-open CIDR blocks, contradicts Zero Trust principles. Instead, use tightly scoped security groups, precise IAM roles, and target-specific access controls to reduce exposure.
3. Micro-Segmentation
Avoid relying on a single NLB for multiple services. Segment workloads across different NLBs and VPCs to limit potential blast radius in the event of compromise.
4. Continuous Monitoring
AWS provides comprehensive logging and monitoring tools. Utilize VPC flow logs, NLB access logs, and CloudWatch to gain visibility into traffic patterns and detect anomalies. Integrate with AWS Security Hub or third-party tools like Datadog and Splunk for centralized analysis.
Public vs. Private NLBs: Applying the Same Principles
Whether your NLB is public-facing or internal-only, Zero Trust is essential—although implementation tactics may vary:
- Public NLBs: Secure with TLS, IP allow-lists, rate limiting, and potentially a WAF via CloudFront or third-party services to prevent DDoS attacks.
- Private NLBs: Often used in PrivateLink and multi-account setups. Enforce IAM restrictions, monitor access rigorously, and treat internal traffic with the same scrutiny as external traffic.
Implementing Zero Trust With AWS NLB
Follow these best practices to build Zero Trust into your NLB infrastructure:
- Use Private Subnets: Place NLBs in private subnets when possible and apply restrictive security groups.
- TLS Termination: Enable TLS at the NLB level using ACM to ensure secure communication.
- Authentication Layers: Implement service-level authentication using IAM or external systems like Cognito or API Gateway.
- Comprehensive Monitoring: Enable access logs, flow logs, and CloudWatch metrics for real-time insights.
- Leverage PrivateLink: Where possible, route traffic through PrivateLink to avoid exposure to the public internet.
Advanced Security Configurations
For heightened security, consider these additional configurations:
- Preserve Client IP: Retain the source IP to enable geolocation and IP-based access policies.
- DDoS Protection: While AWS Shield Standard is always enabled, consider Shield Advanced for mission-critical services. Pairing with CloudFront and WAF strengthens application-layer security.
- Cross-Zone Configuration Consistency: Ensure consistent security policies, IAM roles, and logging across all availability zones.
- Manual Approval for PrivateLink Endpoints: Require manual approvals to tightly control which consumers can connect to your endpoints.
- Cryptographic Hygiene: Use modern TLS ciphers and ECDSA certificates for improved security and performance.
Final Thoughts
Zero Trust is not a switch to toggle—it’s a security mindset. Applying it to AWS NLBs transforms them from simple traffic routers into secure gateways.
AWS provides all the essential components—static IPs, TLS support, IAM, PrivateLink, and detailed logging. It’s up to the architecture team to assemble these into a cohesive, secure, and scalable solution. By integrating Zero Trust into your NLB architecture, you align security with performance, which is critical in today’s evolving threat landscape.