Zero Trust Architecture Implementation

Comprehensive Zero Trust security architecture for AWS Control Tower Landing Zone.

Executive Summary

This implementation follows the NIST 800-207 Zero Trust Architecture framework, providing defense-in-depth security controls that assume no implicit trust and continuously verify every access request.

Zero Trust Principles

1. Never Trust, Always Verify

MFA Enforcement: Multi-factor authentication required for all users
Continuous Authentication: Every request is authenticated and authorized
Session Management: Secure, audited access via AWS Systems Manager
No SSH/RDP: Direct access protocols disabled

2. Assume Breach

VPC Flow Logs: Complete network traffic monitoring
GuardDuty: Continuous threat detection
CloudTrail: Comprehensive audit logging
Security Hub: Centralized security findings

3. Verify Explicitly

IAM Access Analyzer: Continuous access verification
Log File Validation: Cryptographic verification of logs
Config Rules: Continuous compliance monitoring
Real-time Alerts: Immediate notification of security events

4. Least Privilege Access

No Wildcard Permissions: Explicit permissions only
Temporary Credentials: Short-lived access tokens
Role-based Access: IAM roles instead of users
Just-in-Time Access: Access granted only when needed

5. Segment Access (Micro-segmentation)

Private Subnets: No direct internet access
VPC Endpoints: Private connectivity to AWS services
Security Groups: Default deny with explicit allow rules
Network ACLs: Defense in depth at subnet level

Architecture Components

Network Layer

┌─────────────────────────────────────────────────────────────┐
│                    Zero Trust VPC                            │
│  ┌──────────────────────────────────────────────────────┐  │
│  │              Private Subnets (Multi-AZ)              │  │
│  │  • No Internet Gateway                                │  │
│  │  • VPC Endpoints for AWS services                    │  │
│  │  • Network ACLs for defense in depth                 │  │
│  │  • VPC Flow Logs enabled                             │  │
│  └──────────────────────────────────────────────────────┘  │
│                                                              │
│  ┌──────────────────────────────────────────────────────┐  │
│  │         VPC Endpoints (Private Connectivity)          │  │
│  │  Interface: EC2, SSM, KMS, Secrets, ECR, ECS, Logs   │  │
│  │  Gateway: S3, DynamoDB                                │  │
│  └──────────────────────────────────────────────────────┘  │
└─────────────────────────────────────────────────────────────┘

Identity Layer

┌─────────────────────────────────────────────────────────────┐
│              Identity & Access Management                    │
│  ┌──────────────────────────────────────────────────────┐  │
│  │  AWS IAM Identity Center (SSO)                        │  │
│  │  • Centralized identity management                    │  │
│  │  • MFA enforcement                                    │  │
│  │  • Temporary credentials                              │  │
│  └──────────────────────────────────────────────────────┘  │
│                                                              │
│  ┌──────────────────────────────────────────────────────┐  │
│  │  IAM Access Analyzer                                  │  │
│  │  • Continuous access monitoring                       │  │
│  │  • External access detection                          │  │
│  │  • Policy validation                                  │  │
│  └──────────────────────────────────────────────────────┘  │
│                                                              │
│  ┌──────────────────────────────────────────────────────┐  │
│  │  AWS Verified Access                                  │  │
│  │  • Zero Trust network access                          │  │
│  │  • Context-aware authorization                        │  │
│  │  • No VPN required                                    │  │
│  └──────────────────────────────────────────────────────┘  │
└─────────────────────────────────────────────────────────────┘

Application Layer

┌─────────────────────────────────────────────────────────────┐
│              Application Protection                          │
│  ┌──────────────────────────────────────────────────────┐  │
│  │  AWS WAF                                              │  │
│  │  • Rate limiting                                      │  │
│  │  • Geo-blocking                                       │  │
│  │  • Managed rule sets                                  │  │
│  │  • Custom security rules                              │  │
│  └──────────────────────────────────────────────────────┘  │
│                                                              │
│  ┌──────────────────────────────────────────────────────┐  │
│  │  AWS PrivateLink                                      │  │
│  │  • Service-to-service communication                   │  │
│  │  • No internet exposure                               │  │
│  │  • Private connectivity                               │  │
│  └──────────────────────────────────────────────────────┘  │
└─────────────────────────────────────────────────────────────┘

Data Layer

┌─────────────────────────────────────────────────────────────┐
│              Data Protection                                 │
│  ┌──────────────────────────────────────────────────────┐  │
│  │  Encryption at Rest                                   │  │
│  │  • AWS KMS for key management                         │  │
│  │  • Automatic key rotation                             │  │
│  │  • Encrypted EBS, S3, RDS, ElastiCache               │  │
│  └──────────────────────────────────────────────────────┘  │
│                                                              │
│  ┌──────────────────────────────────────────────────────┐  │
│  │  Encryption in Transit                                │  │
│  │  • TLS 1.2+ for all communications                    │  │
│  │  • Certificate management                             │  │
│  │  • Perfect forward secrecy                            │  │
│  └──────────────────────────────────────────────────────┘  │
│                                                              │
│  ┌──────────────────────────────────────────────────────┐  │
│  │  AWS Secrets Manager                                  │  │
│  │  • Secure credential storage                          │  │
│  │  • Automatic rotation                                 │  │
│  │  • Audit logging                                      │  │
│  └──────────────────────────────────────────────────────┘  │
└─────────────────────────────────────────────────────────────┘

Implementation Guide

Step 1: Deploy Zero Trust Module

module "zero_trust" {
  source = "./modules/zero-trust"

  name_prefix        = var.project_name
  region             = var.home_region
  vpc_cidr           = "10.100.0.0/16"
  availability_zones = ["ap-southeast-2a", "ap-southeast-2b", "ap-southeast-2c"]
  
  kms_key_id          = module.security.kms_key_id
  sns_topic_arn       = aws_sns_topic.security.arn
  session_logs_bucket = module.logging.log_bucket_name
  
  enable_verified_access = true
  enable_privatelink     = true
  enable_waf             = true
  
  tags = local.common_tags
}

Step 2: Configure IAM Identity Center

Enable IAM Identity Center in management account
Configure identity source (Active Directory, Okta, etc.)
Create permission sets with least privilege
Assign users to accounts and permission sets
Enable MFA for all users

Step 3: Implement Network Segmentation

Deploy workloads in private subnets
Configure VPC endpoints for AWS services
Remove internet gateways from workload VPCs
Implement security groups with default deny
Enable VPC Flow Logs

Step 4: Enable Monitoring

Configure CloudWatch alarms
Set up EventBridge rules
Enable GuardDuty
Enable Security Hub
Configure SNS notifications

Step 5: Enforce Policies

Apply OPA Zero Trust policies
Enable AWS Config rules
Implement SCPs for guardrails
Regular policy reviews

Security Controls

Identity Controls

Control	Implementation	Status
MFA Enforcement	IAM policy denies actions without MFA	✅ Implemented
No Long-term Credentials	IAM roles with temporary credentials	✅ Implemented
Access Analyzer	Continuous monitoring of resource access	✅ Implemented
Session Manager	Secure access without SSH/RDP	✅ Implemented
Verified Access	Zero Trust network access	✅ Implemented

Network Controls

Control	Implementation	Status
Private Subnets	No internet gateway	✅ Implemented
VPC Endpoints	Private AWS service access	✅ Implemented
VPC Flow Logs	Complete traffic logging	✅ Implemented
Network ACLs	Defense in depth	✅ Implemented
Security Groups	Default deny	✅ Implemented

Application Controls

Control	Implementation	Status
WAF Protection	Rate limiting, geo-blocking	✅ Implemented
PrivateLink	Service-to-service communication	✅ Implemented
TLS Everywhere	Encryption in transit	✅ Implemented
API Gateway	Centralized API management	🔄 Optional
App Mesh	Service mesh for microservices	🔄 Optional

Data Controls

Control	Implementation	Status
KMS Encryption	All data at rest encrypted	✅ Implemented
Key Rotation	Automatic key rotation	✅ Implemented
Secrets Manager	Secure credential storage	✅ Implemented
S3 Encryption	Mandatory bucket encryption	✅ Implemented
RDS Encryption	Database encryption	✅ Implemented

Monitoring Controls

Control	Implementation	Status
CloudTrail	API call logging	✅ Implemented
GuardDuty	Threat detection	✅ Implemented
Security Hub	Centralized findings	✅ Implemented
Config	Compliance monitoring	✅ Implemented
CloudWatch	Metrics and alarms	✅ Implemented

Compliance Mapping

NIST 800-207 Zero Trust Architecture

Tenet	Implementation	Evidence
Data sources and computing services are considered resources	All AWS resources treated as untrusted	VPC endpoints, private subnets
All communication is secured regardless of network location	TLS everywhere, VPC endpoints	Encryption in transit
Access to individual enterprise resources is granted on a per-session basis	Temporary credentials, session manager	IAM roles, SSM
Access to resources is determined by dynamic policy	IAM policies, security groups	Policy-based access
The enterprise monitors and measures the integrity and security posture of all owned and associated assets	GuardDuty, Security Hub, Config	Continuous monitoring
All resource authentication and authorization are dynamic and strictly enforced before access is allowed	MFA, Access Analyzer	Identity verification
The enterprise collects as much information as possible about the current state of assets, network infrastructure and communications	CloudTrail, VPC Flow Logs	Comprehensive logging

NIST 800-53 Controls

AC-2: Account Management (IAM Identity Center)
AC-3: Access Enforcement (Security groups, NACLs)
AC-6: Least Privilege (IAM policies)
AU-2: Audit Events (CloudTrail, VPC Flow Logs)
AU-6: Audit Review (GuardDuty, Security Hub)
IA-2: Identification and Authentication (MFA)
SC-7: Boundary Protection (VPC, security groups)
SC-8: Transmission Confidentiality (TLS)
SC-13: Cryptographic Protection (KMS)
SI-4: Information System Monitoring (CloudWatch)

Operational Procedures

Daily Operations

Monitor Security Dashboard
- Review GuardDuty findings
- Check Security Hub compliance score
- Review CloudWatch alarms
Access Reviews
- Review Access Analyzer findings
- Validate temporary access grants
- Audit session manager activity
Incident Response
- Investigate security alerts
- Review CloudTrail logs
- Document findings

Weekly Operations

Policy Reviews
- Review IAM policies
- Validate security group rules
- Check VPC endpoint usage
Compliance Checks
- Run Config compliance reports
- Review OPA policy violations
- Update remediation plans

Monthly Operations

Access Certification
- Review user access
- Validate role assignments
- Remove unused permissions
Security Assessments
- Run vulnerability scans
- Review architecture changes
- Update threat models

Troubleshooting

Common Issues

Issue: Cannot access AWS services from private subnet

Solution: Verify VPC