1. Solution Overview

The proposed solution is a cloud-native, microservices-based, event-driven architecture designed to handle millions of concurrent users with sub-second response times. The platform leverages AWS managed services to achieve 99.99% availability, horizontal scalability, and global reach while maintaining strong consistency for booking transactions.

Key Business Objectives:

• Handle 10M+ daily active users with <200ms API response times
• Process 1M+ events per second for real-time personalization
• Ensure zero double-bookings through strong consistency guarantees
• Support multi-region deployment for global low-latency access
• Achieve <1 hour RTO and <5 minutes RPO for disaster recovery

Architectural Patterns: Microservices architecture with event-driven communication, CQRS (Command Query Responsibility Segregation) for read/write separation, Lambda architecture for real-time and batch processing, and API Gateway pattern for unified access.

2. Architecture Components

AWS Services & Resources

Compute Layer

• Amazon EKS (v1.28): Managed Kubernetes for core microservices

• Node Groups: m6i.2xlarge (8 vCPU, 32 GB RAM) for stateless services

• Spot instances for non-critical workloads (70% cost reduction)

• Auto-scaling: 10-100 nodes based on CPU >70% and custom metrics

• AWS Lambda: Serverless functions for event processing

• Memory: 1024-3096 MB based on function complexity

• Timeout: 30-900 seconds for async operations

• Provisioned concurrency for latency-sensitive functions

• AWS Fargate: Container orchestration for batch jobs and admin services

• Task definitions: 2-4 vCPU, 8-16 GB memory

Database Layer

• Amazon Aurora PostgreSQL Global Database (v15.4): Primary transactional database

• Instance type: db.r6g.4xlarge (16 vCPU, 128 GB RAM)

• Multi-AZ: 1 primary + 2 read replicas per region

• Cross-region replicas in 2 additional regions (us-east-1, eu-west-1, ap-southeast-1)

• Storage: Auto-scaling from 10GB to 128TB

• Amazon DynamoDB Global Tables: User sessions, preferences, and real-time signals

• On-demand capacity mode for unpredictable traffic

• Point-in-time recovery enabled

• DAX cluster (dax.r5.large) for <1ms read latency

• Amazon ElastiCache for Redis (v7.0): Multi-tier caching

• Cluster mode: cache.r6g.xlarge (4 vCPU, 26.32 GB RAM)

• 3 nodes per shard, 3 shards for horizontal scaling

• Global Datastore for multi-region caching

• Amazon OpenSearch (v2.11): Search engine for property listings

• Instance type: r6g.2xlarge.search (8 vCPU, 64 GB RAM)

• 3 master nodes, 6 data nodes across 3 AZs

• 500GB EBS gp3 storage per node (16,000 IOPS)

Storage Layer

• Amazon S3: Object storage for media assets

• Standard tier: Property images, documents

• Intelligent-Tiering: User uploads with lifecycle policies

• Glacier Flexible Retrieval: Archival data >90 days

• Versioning enabled with MFA delete protection

• Amazon EFS: Shared file system for containerized applications

• Performance mode: General Purpose

• Throughput mode: Elastic (auto-scales)

• 100GB provisioned capacity

Networking Layer

• Amazon VPC: Multi-tier network architecture

• CIDR: 10.0.0.0/16 (65,536 IPs)

• Public subnets: 10.0.1.0/24, 10.0.2.0/24, 10.0.3.0/24 (per AZ)

• Private app subnets: 10.0.11.0/24, 10.0.12.0/24, 10.0.13.0/24

• Private data subnets: 10.0.21.0/24, 10.0.22.0/24, 10.0.23.0/24

• NAT Gateways: 3 (one per AZ) in public subnets

• Application Load Balancer (ALB): Layer 7 load balancing

• Internet-facing ALB for external traffic

• Internal ALB for microservices communication

• Sticky sessions with cookie-based routing

• Connection draining: 300 seconds

• Amazon CloudFront: Global CDN with 450+ edge locations

• Origin: S3 (static assets) and ALB (dynamic content)

• Cache TTL: 86400s (static), 0s (dynamic with smart caching)

• Origin shield enabled for reduced origin load

• Field-level encryption for sensitive data

• Amazon Route 53: DNS with health checks and failover

• Latency-based routing for global users

• Failover routing to secondary region

• Health checks every 30 seconds

Security Services

• AWS IAM: Role-based access control

• Service accounts for each microservice with least privilege

• OIDC provider integration for EKS pod identities

• MFA enforcement for console access

• AWS Secrets Manager: Secrets and credentials management

• Automatic rotation every 30 days

• Encryption with customer-managed KMS keys

• AWS KMS: Encryption key management

• Customer-managed keys for Aurora, DynamoDB, S3

• Automatic key rotation annually

• CloudHSM integration for high-security requirements

• AWS WAF: Web application firewall

• Managed rule groups: Core rule set, SQL injection, XSS

• Rate limiting: 2000 requests per 5 minutes per IP

• Geo-blocking for sanctioned countries

• AWS Shield Advanced: DDoS protection

• 24/7 DDoS response team access

• Cost protection for scaling during attacks

• Amazon GuardDuty: Threat detection

• Continuous monitoring for malicious activity

• Integration with EventBridge for automated response

• AWS Security Hub: Centralized security posture

• CIS AWS Foundations Benchmark compliance

• Automated remediation with Lambda

Monitoring & Logging

• Amazon CloudWatch: Metrics, logs, and alarms

• Metrics: Custom application metrics with 1-minute resolution

• Logs: Centralized logging with 90-day retention

• Alarms: 50+ alarms for critical metrics (CPU, memory, latency, errors)

• Dashboards: Real-time operational dashboards

• AWS X-Ray: Distributed tracing

• Sampling rate: 10% for normal traffic, 100% for errors

• Service map visualization for dependency analysis

• AWS CloudTrail: API audit logging

• Multi-region trail enabled

• Log file integrity validation

• S3 lifecycle to Glacier after 90 days

CI/CD Services

• AWS CodePipeline: Orchestration of deployment pipeline

• Source: GitHub with webhook triggers

• Build stage: CodeBuild for Docker image creation

• Deploy stage: EKS with blue-green deployment

• AWS CodeBuild: Container image building

• Build spec: Docker multi-stage builds

• Cache: S3-backed for faster builds

• Compute: BUILD_GENERAL1_LARGE (8 GB memory, 4 vCPUs)

• AWS CodeDeploy: Deployment automation

• Deployment configuration: Blue-green with 10% traffic shifting every 5 minutes

• Automatic rollback on CloudWatch alarm breach

Additional Managed Services

• Amazon EventBridge: Event bus for microservices communication

• Custom event buses per domain (bookings, properties, users)

• Event archive with 30-day retention

• Amazon SQS: Asynchronous task queues

• Standard queues for non-critical processing

• FIFO queues for ordered operations (booking confirmation)

• Dead-letter queues with 14-day retention

• Amazon SNS: Pub/sub notifications

• Topics for email, SMS, and mobile push notifications

• Message filtering for targeted delivery

• Amazon SES: Transactional email delivery

• Dedicated IP pool for reputation management

• Open and click tracking enabled

• Amazon Cognito: User authentication and authorization

• User pools: 10M+ users with MFA support

• Identity pools for temporary AWS credentials

• Social login: Google, Facebook, Apple

• AWS Step Functions: Workflow orchestration

• Booking workflow: Search → Reserve → Payment → Confirm

• Express workflows for high-throughput operations

Infrastructure-as-Code Tools

Terraform (v1.6+): Primary IaC tool for AWS resource provisioning

• Why Terraform: Multi-cloud compatibility, rich ecosystem, state management with S3 backend and DynamoDB locking, extensive AWS provider support, reusable modules for consistency

• Module Structure:

• terraform/modules/networking: VPC, subnets, security groups

• terraform/modules/compute: EKS, Lambda, Fargate

• terraform/modules/database: Aurora, DynamoDB, ElastiCache

• terraform/modules/storage: S3, EFS

• terraform/modules/security: IAM roles, KMS, Secrets Manager

• Remote State: S3 bucket booking-platform-tfstate with versioning and encryption

Helm (v3.13+): Kubernetes package manager for application deployment

• Charts for each microservice with configurable values
• Shared charts for common patterns (monitoring, ingress)

AWS CDK (TypeScript v2.110+): For complex Step Functions workflows and Lambda functions

• Type safety for infrastructure code
• High-level constructs for patterns

Third-Party Tools/Platforms

Container Orchestration

• Kubernetes v1.28: Container orchestration platform

• Helm Charts: Custom charts for microservices

• Kustomize: Environment-specific overlays (dev, staging, prod)

• ArgoCD (v2.9+): GitOps continuous delivery

• Automated sync from Git repositories

• Self-healing capabilities

• Multi-cluster management

CI/CD Platforms

• GitHub Actions: CI pipeline for testing and building

• Workflow: Lint → Test → Security scan → Build → Push to ECR

• Self-hosted runners on EC2 for faster builds

• ArgoCD: CD for Kubernetes deployments

Monitoring & Observability

• Prometheus (v2.48+): Metrics collection and storage

• Scrape interval: 30 seconds

• Retention: 15 days

• Node exporter, kube-state-metrics for cluster insights

• Grafana (v10.2+): Visualization and dashboards

• 20+ pre-built dashboards for infrastructure and application metrics

• Alerting integration with PagerDuty and Slack

• Datadog: APM and log management (alternative/supplementary)

• Distributed tracing across microservices

• Real user monitoring (RUM) for frontend performance

Security & Compliance

• Trivy: Container image vulnerability scanning

• Integrated in CI pipeline with severity threshold: HIGH

• Falco: Runtime security monitoring in Kubernetes

• Detects anomalous behavior in containers

• OPA/Gatekeeper: Policy enforcement in Kubernetes

• Admission controller for policy validation

• Policies for resource limits, image registries, network policies

Message Streaming

• Apache Kafka on Amazon MSK (v3.6): Event streaming platform

• Cluster: kafka.m5.2xlarge (8 vCPU, 32 GB RAM) × 6 brokers

• Partition: 100 partitions per topic

• Retention: 7 days

• Topics: user-events, booking-events, property-updates, payment-events

Programming Languages & Frameworks

Application Layer

• Node.js (v20 LTS): User service, search service, recommendation service

• Framework: NestJS for enterprise-grade architecture

• ORM: Prisma for database access with type safety

• Java (OpenJDK 17): Booking service, payment service

• Framework: Spring Boot 3.2 with Spring Cloud for microservices patterns

• Reactive programming with Project Reactor for high concurrency

• Python (v3.11): ML/recommendation engine, data processing pipelines

• Framework: FastAPI for high-performance APIs

• Libraries: Pandas, NumPy, scikit-learn, TensorFlow

• Go (v1.21): API Gateway, notification service (high-performance services)

• Framework: Gin for HTTP routing

• gRPC for inter-service communication

Frontend

• React (v18) with Next.js (v14) for server-side rendering
• TypeScript for type safety
• Redux Toolkit for state management

Scripting & Automation

• Python: AWS Lambda functions, automation scripts
• Bash: Infrastructure maintenance scripts
• TypeScript: AWS CDK infrastructure code

Data Processing

• Apache Flink (v1.18): Stream processing

• Deployed on EKS with 20 task managers

• Checkpointing every 5 minutes to S3

Hardware/Compute Specifications

EKS Node Groups

General Purpose (Microservices)

• Instance type: m6i.2xlarge

• vCPU: 8, Memory: 32 GB, Network: Up to 12.5 Gbps

• Rationale: Balanced compute/memory for stateless services

• Auto-scaling: 10-100 nodes

• Scale-up: CPU >70% for 3 minutes

• Scale-down: CPU <30% for 10 minutes

• Pod limits: 58 pods per node

Memory-Optimized (Caching/Data Services)

• Instance type: r6i.2xlarge

• vCPU: 8, Memory: 64 GB

• Rationale: High memory for caching layers and data processing

• Auto-scaling: 3-20 nodes

Compute-Optimized (CPU-Intensive Tasks)

• Instance type: c6i.4xlarge

• vCPU: 16, Memory: 32 GB

• Rationale: ML inference, search indexing

• Auto-scaling: 2-15 nodes

Lambda Configurations

• API Functions: 1024 MB, 30s timeout, 1000 concurrent executions
• Event Processors: 2048 MB, 300s timeout, 5000 concurrent executions
• Scheduled Jobs: 3008 MB, 900s timeout, 10 concurrent executions

RDS/Aurora Instances

• Production: db.r6g.4xlarge

• vCPU: 16, Memory: 128 GB, Network: Up to 10 Gbps

• Connection pool: 500 max connections per instance

• Read Replicas: db.r6g.2xlarge (2 per region)

ElastiCache Clusters

• Instance: cache.r6g.xlarge

• vCPU: 4, Memory: 26.32 GB

• Cluster: 3 shards × 3 nodes = 9 nodes total

• Max connections: 65,000 per node

OpenSearch Nodes

• Master nodes: r6g.large.search (3 nodes)

• Data nodes: r6g.2xlarge.search (6 nodes)

• vCPU: 8, Memory: 64 GB, Storage: 500GB gp3 EBS

3. Architecture Diagram

┌─────────────────────────────────────────────────────────────────────────────┐
│                           REGION: us-east-1 (Primary)                        │
│  ┌──────────────────────────────────────────────────────────────────────┐   │
│  │                         Global Services Layer                         │   │
│  │  ┌────────────┐  ┌─────────────┐  ┌──────────────┐  ┌─────────────┐│   │
│  │  │ Route 53   │  │ CloudFront  │  │    WAF       │  │   Shield    ││   │
│  │  │(Latency    │  │(CDN: 450+   │  │(Rate Limit:  │  │  Advanced   ││   │
│  │  │ Routing)   │  │ Edge Locs)  │  │ 2K req/5min) │  │  (DDoS)     ││   │
│  │  └─────┬──────┘  └──────┬──────┘  └──────┬───────┘  └─────────────┘│   │
│  └────────┼─────────────────┼─────────────────┼──────────────────────────┘   │
│           │                 │                 │                              │
│  ┌────────▼─────────────────▼─────────────────▼──────────────────────────┐   │
│  │                    VPC: 10.0.0.0/16 (3 AZs)                           │   │
│  │                                                                        │   │
│  │  ┌──────────────────────────────────────────────────────────────┐    │   │
│  │  │              PUBLIC SUBNETS (10.0.1-3.0/24)                   │    │   │
│  │  │  ┌──────────────────┐  ┌──────────────────┐  ┌────────────┐ │    │   │
│  │  │  │  Internet-facing │  │   NAT Gateway    │  │   Bastion  │ │    │   │
│  │  │  │       ALB        │  │  (3 per AZ)      │  │    Host    │ │    │   │
│  │  │  │ (HTTPS:443)      │  │                  │  │ (Mgmt Only)│ │    │   │
│  │  │  └────────┬─────────┘  └────────┬─────────┘  └────────────┘ │    │   │
│  │  └───────────┼──────────────────────┼──────────────────────────┘    │   │
│  │              │                      │                                │   │
│  │  ┌───────────▼──────────────────────▼────────────────────────────┐  │   │
│  │  │         PRIVATE APP SUBNETS (10.0.11-13.0/24)                 │  │   │
│  │  │  ┌──────────────────────────────────────────────────────────┐ │  │   │
│  │  │  │        Amazon EKS Cluster (k8s v1.28)                     │ │  │   │
│  │  │  │  ┌─────────────┐  ┌──────────────┐  ┌─────────────────┐ │ │  │   │
│  │  │  │  │   User      │  │   Property   │  │    Booking      │ │ │  │   │
│  │  │  │  │   Service   │  │   Service    │  │    Service      │ │ │  │   │
│  │  │  │  │  (Node.js)  │  │  (Node.js)   │  │    (Java)       │ │ │  │   │
│  │  │  │  │  3-10 pods  │  │  5-20 pods   │  │   5-30 pods     │ │ │  │   │
│  │  │  │  └──────┬──────┘  └──────┬───────┘  └────────┬────────┘ │ │  │   │
│  │  │  │  ┌──────▼──────┐  ┌──────▼───────┐  ┌────────▼────────┐ │ │  │   │
│  │  │  │  │   Search    │  │   Payment    │  │  Notification   │ │ │  │   │
│  │  │  │  │   Service   │  │   Service    │  │    Service      │ │ │  │   │
│  │  │  │  │  (Node.js)  │  │   (Java)     │  │     (Go)        │ │ │  │   │
│  │  │  │  │  5-15 pods  │  │  3-15 pods   │  │   2-10 pods     │ │ │  │   │
│  │  │  │  └──────┬──────┘  └──────┬───────┘  └────────┬────────┘ │ │  │   │
│  │  │  │         │                │                    │           │ │  │   │
│  │  │  │  ┌──────▼────────────────▼────────────────────▼────────┐ │ │  │   │
│  │  │  │  │         Internal Application Load Balancer          │ │ │  │   │
│  │  │  │  └──────────────────────────────────────────────────────┘ │ │  │   │
│  │  │  └──────────────────────────────────────────────────────────┘ │  │   │
│  │  │                                                                 │  │   │
│  │  │  ┌──────────────────────────────────────────────────────────┐ │  │   │
│  │  │  │           Lambda Functions (Serverless Layer)            │ │  │   │
│  │  │  │  • Event Processors (User Signals Processing)            │ │  │   │
│  │  │  │  • Image Processing (Thumbnails, Optimization)           │ │  │   │
│  │  │  │  • Scheduled Jobs (Reports, Cleanup)                     │ │  │   │
│  │  │  │  • Stream Processing (Kafka → DynamoDB)                  │ │  │   │
│  │  │  └──────────────────────────────────────────────────────────┘ │  │   │
│  │  │                                                                 │  │   │
│  │  │  ┌──────────────────────────────────────────────────────────┐ │  │   │
│  │  │  │        Event-Driven Architecture Components              │ │  │   │
│  │  │  │  ┌────────────────┐  ┌──────────────┐  ┌──────────────┐ │ │  │   │
│  │  │  │  │  EventBridge   │  │     SQS      │  │     SNS      │ │ │  │   │
│  │  │  │  │ (Event Bus)    │  │  (Queues)    │  │  (Pub/Sub)   │ │ │  │   │
│  │  │  │  └────────────────┘  └──────────────┘  └──────────────┘ │ │  │   │
│  │  │  │  ┌────────────────────────────────────────────────────┐ │ │  │   │
│  │  │  │  │   Amazon MSK (Kafka v3.6 - 6 Brokers)              │ │ │  │   │
│  │  │  │  │   Topics: user-events, booking-events, payments    │ │ │  │   │
│  │  │  │  └────────────────────────────────────────────────────┘ │ │  │   │
│  │  │  └──────────────────────────────────────────────────────────┘ │  │   │
│  │  └─────────────────────────────────────────────────────────────┘  │   │
│  │                                                                     │   │
│  │  ┌──────────────────────────────────────────────────────────────┐ │   │
│  │  │         PRIVATE DATA SUBNETS (10.0.21-23.0/24)               │ │   │
│  │  │                                                               │ │   │
│  │  │  ┌────────────────────────────────────────────────────────┐  │ │   │
│  │  │  │     Aurora PostgreSQL Global Database (v15.4)          │  │ │   │
│  │  │  │  Primary: db.r6g.4xlarge (16 vCPU, 128GB)             │  │ │   │
│  │  │  │  Read Replicas: 2x db.r6g.2xlarge per region          │  │ │   │
│  │  │  │  Cross-region replication: <1s latency                 │  │ │   │
│  │  │  └────────────────────────────────────────────────────────┘  │ │   │
│  │  │                                                               │ │   │
│  │  │  ┌────────────────────────────────────────────────────────┐  │ │   │
│  │  │  │        DynamoDB Global Tables (On-Demand)              │  │ │   │
│  │  │  │  • user-sessions (TTL: 24h)                            │  │ │   │
│  │  │  │  • user-preferences                                    │  │ │   │
│  │  │  │  • user-signals (real-time events)                     │  │ │   │
│  │  │  │  • booking-state-machine                               │  │ │   │
│  │  │  │  + DAX Cluster (dax.r5.large - <1ms reads)            │  │ │   │
│  │  │  └────────────────────────────────────────────────────────┘  │ │   │
│  │  │                                                               │ │   │
│  │  │  ┌────────────────────────────────────────────────────────┐  │ │   │
│  │  │  │    ElastiCache Redis Global Datastore (v7.0)          │  │ │   │
│  │  │  │  3 shards × 3 nodes (cache.r6g.xlarge)                │  │ │   │
│  │  │  │  Use cases: Session cache, API cache, Rate limiting   │  │ │   │
│  │  │  └────────────────────────────────────────────────────────┘  │ │   │
│  │  │                                                               │ │   │
│  │  │  ┌────────────────────────────────────────────────────────┐  │ │   │
│  │  │  │       Amazon OpenSearch Service (v2.11)                │  │ │   │
│  │  │  │  Master: 3x r6g.large.search (HA)                     │  │ │   │
│  │  │  │  Data: 6x r6g.2xlarge.search (500GB gp3 each)         │  │ │   │
│  │  │  │  Indices: properties, users, bookings                  │  │ │   │
│  │  │  └────────────────────────────────────────────────────────┘  │ │   │
│  │  └───────────────────────────────────────────────────────────────┘ │   │
│  │                                                                     │   │
│  │  ┌──────────────────────────────────────────────────────────────┐ │   │
│  │  │                   Storage & CDN Layer                         │ │   │
│  │  │  ┌────────────────────────────────────────────────────────┐  │ │   │
│  │  │  │              Amazon S3 (Multi-Region)                  │  │ │   │
│  │  │  │  • booking-platform-media (Images, Videos)             │  │ │   │
│  │  │  │  • booking-platform-documents (Contracts, IDs)         │  │ │   │
│  │  │  │  • booking-platform-backups (DB dumps, Snapshots)      │  │ │   │
│  │  │  │  • booking-platform-logs (CloudWatch, Access logs)     │  │ │   │
│  │  │  │  Versioning: Enabled | MFA Delete: Enabled             │  │ │   │
│  │  │  │  Lifecycle: Standard → Intelligent-Tiering → Glacier   │  │ │   │
│  │  │  └────────────────────────────────────────────────────────┘  │ │   │
│  │  │                                                               │ │   │
│  │  │  ┌────────────────────────────────────────────────────────┐  │ │   │
│  │  │  │        Amazon EFS (Shared File System)                 │  │ │   │
│  │  │  │  Mount targets in each AZ for EKS pods                │  │ │   │
│  │  │  │  Performance: General Purpose | Throughput: Elastic    │  │ │   │
│  │  │  └────────────────────────────────────────────────────────┘  │ │   │
│  │  └───────────────────────────────────────────────────────────────┘ │   │
│  │                                                                     │   │
│  │  ┌──────────────────────────────────────────────────────────────┐ │   │
│  │  │              Security & Identity Services                     │ │   │
│  │  │  ┌──────────────┐  ┌────────────┐  ┌────────────────────┐   │ │   │
│  │  │  │   Cognito    │  │    IAM     │  │  Secrets Manager   │   │ │   │
│  │  │  │ (User Pools) │  │  (Roles)   │  │  (DB Creds, API)   │   │ │   │
│  │  │  └──────────────┘  └────────────┘  └────────────────────┘   │ │   │
│  │  │  ┌──────────────┐  ┌────────────┐  ┌────────────────────┐   │ │   │
│  │  │  │     KMS      │  │ GuardDuty  │  │  Security Hub      │   │ │   │
│  │  │  │(CMK for all) │  │(Threat Det)│  │(CIS Compliance)    │   │ │   │
│  │  │  └──────────────┘  └────────────┘  └────────────────────┘   │ │   │
│  │  └───────────────────────────────────────────────────────────────┘ │   │
│  │                                                                     │   │
│  │  ┌──────────────────────────────────────────────────────────────┐ │   │
│  │  │            Monitoring & Observability Stack                   │ │   │
│  │  │  ┌────────────────────────────────────────────────────────┐  │ │   │
│  │  │  │  CloudWatch (Metrics, Logs, Alarms, Dashboards)        │  │ │   │
│  │  │  │  • 50+ alarms (CPU, Memory, Latency, Error Rate)       │  │ │   │
│  │  │  │  • Log retention: 90 days                              │  │ │   │
│  │  │  │  • Custom metrics: 1-min resolution                    │  │ │   │
│  │  │  └────────────────────────────────────────────────────────┘  │ │   │
│  │  │  ┌────────────────────────────────────────────────────────┐  │ │   │
│  │  │  │  Prometheus + Grafana (on EKS)                         │  │ │   │
│  │  │  │  • 20+ dashboards (Infrastructure + Application)       │  │ │   │
│  │  │  │  • Alerting: PagerDuty, Slack integration              │  │ │   │
│  │  │  └────────────────────────────────────────────────────────┘  │ │   │
│  │  │  ┌────────────────────────────────────────────────────────┐  │ │   │
│  │  │  │  AWS X-Ray (Distributed Tracing)                       │  │ │   │
│  │  │  │  • Service map visualization                           │  │ │   │
│  │  │  │  • Sampling: 10% normal, 100% errors                   │  │ │   │
│  │  │  └────────────────────────────────────────────────────────┘  │ │   │
│  │  └───────────────────────────────────────────────────────────────┘ │   │
│  └─────────────────────────────────────────────────────────────────┘   │
│                                                                          │
│  ┌──────────────────────────────────────────────────────────────────┐  │
│  │                        CI/CD Pipeline                             │  │
│  │  GitHub → GitHub Actions → CodeBuild → ECR → ArgoCD → EKS       │  │
│  │  (Source)   (Test/Scan)    (Build)    (Registry) (Deploy)       │  │
│  └──────────────────────────────────────────────────────────────────┘  │
└─────────────────────────────────────────────────────────────────────────┘

┌─────────────────────────────────────────────────────────────────────────────┐
│              SECONDARY REGIONS: eu-west-1, ap-southeast-1                    │
│  • Aurora read replicas (cross-region replication <1s)                      │
│  • DynamoDB Global Tables (bidirectional replication)                       │
│  • ElastiCache Global Datastore (sub-second replication)                    │
│  • S3 Cross-Region Replication (CRR) for critical data                      │
│  • CloudFront edge caching for regional users                               │
│  • Route 53 latency-based routing to nearest region                         │
└─────────────────────────────────────────────────────────────────────────────┘

Security Boundaries:
━━━━━━━━━━━━━━━━━━━
• Public Subnets: Internet Gateway, ALB, NAT Gateway
• Private App Subnets: EKS, Lambda (outbound via NAT)
• Private Data Subnets: RDS, ElastiCache, OpenSearch (no internet)
• Security Groups: Least privilege port access
• NACLs: Subnet-level protection
• WAF: Layer 7 filtering at CloudFront/ALB

Data Flow:

1. User requests hit Route 53 → CloudFront (cached static content) → WAF filtering → ALB
2. ALB routes to appropriate microservice in EKS based on path
3. Microservices read from ElastiCache (cache hit) or query Aurora/DynamoDB (cache miss)
4. Search queries go to OpenSearch for property listings
5. Booking transactions write to Aurora with strong consistency, emit events to EventBridge/Kafka
6. Event processors (Lambda/Flink) consume events, update DynamoDB user signals
7. Asynchronous tasks (notifications, analytics) processed via SQS/SNS
8. Static assets served from S3 via CloudFront with edge caching

4. High Availability & Disaster Recovery

Multi-AZ Deployment Strategy

• Application Layer: EKS nodes distributed across 3 AZs (us-east-1a, us-east-1b, us-east-1c) with pod anti-affinity rules ensuring service replicas run in different AZs
• Database Layer: Aurora Multi-AZ with 1 primary + 2 read replicas, automatic failover in <30 seconds
• Cache Layer: ElastiCache cluster mode with 3 shards, each with nodes in 3 AZs for 99.99% availability
• Load Balancers: ALB cross-zone load balancing enabled, health checks every 30 seconds with 2 consecutive failures triggering deregistration

Auto-Scaling Policies

EKS Cluster Auto-scaling:

• Horizontal Pod Autoscaler (HPA): Target CPU 70%, memory 75%, custom metrics (request rate >1000/sec per pod)
• Cluster Autoscaler: Adds nodes when pods are unschedulable due to resource constraints
• Karpenter (alternative): Provisions nodes in <1 minute based on pod requirements

Target Tracking Policies:

• Booking Service: Scale when p99 latency >500ms
• Search Service: Scale when request queue depth >100
• Payment Service: Scale when active connections >80% of max

Backup and Restore Procedures

Aurora Automated Backups:

• Continuous backup to S3 with point-in-time recovery (PITR) to any second within retention period
• Retention: 35 days
• Backup window: 02:00-04:00 UTC (low-traffic period)
• Cross-region backup copy to us-west-2 for geographic redundancy

DynamoDB Backups:

• Point-in-time recovery enabled (continuous backups for 35 days)
• On-demand backups weekly, retained for 90 days
• Cross-region replication via Global Tables provides automatic DR

S3 Versioning & Lifecycle:

• Object versioning enabled for all buckets
• Cross-Region Replication (CRR) to us-west-2 for critical data
• MFA delete protection on production buckets

EKS etcd Backups:

• Velero for Kubernetes backup to S3
• Daily full backups, retained for 30 days
• Includes persistent volumes, secrets, configmaps

RTO/RPO Targets

Component	RPO	RTO	Strategy
Aurora Database	<5 minutes	<1 hour	Multi-AZ + PITR + Cross-region replica promotion
DynamoDB	<1 minute	<15 minutes	Global Tables with continuous replication
ElastiCache	<1 minute	<30 minutes	Multi-AZ cluster with automatic failover
EKS Workloads	0 (stateless)	<15 minutes	Multi-AZ pods + ArgoCD auto-sync redeploy
S3 Data	0	<5 minutes	Cross-region replication + 99.999999999% durability
Overall System	<5 minutes	<1 hour	Regional failover with Route 53 health checks

Failover Mechanisms

Database Failover:

• Aurora: Automatic failover to standby replica in 30-120 seconds, DNS endpoint remains same
• Global Database: Manual promotion of secondary region in <1 minute for DR scenario
• Connection pooling with retry logic handles transient failures

Application Failover:

• Route 53 health checks monitor ALB endpoint every 30 seconds
• Failure threshold: 3 consecutive failures (90 seconds detection)
• Automatic DNS failover to secondary region (eu-west-1) with 60-second TTL
• Multi-region active-passive with warm standby (10% capacity in secondary)

Automated Healing:

• EKS: Failed pods automatically restarted by kubelet, rescheduled by kube-scheduler
• ALB: Unhealthy targets removed from rotation, health checks every 30 seconds
• Lambda: Automatic retry with exponential backoff for failed invocations

5. Security Implementation

Network Security

Security Groups (Stateful Firewall):

• sg-alb-public: Port 443 (HTTPS) from 0.0.0.0/0, Port 80 (HTTP redirect) from 0.0.0.0/0
• sg-eks-nodes: Port 443 from ALB SG, inter-node communication (all ports from same SG), ephemeral ports for outbound responses
• sg-aurora-db: Port 5432 from EKS nodes SG and Lambda SG only
• sg-elasticache: Port 6379 from EKS nodes SG only
• sg-opensearch: Port 443 from EKS nodes SG only
• sg-lambda: Outbound to databases, SQS, DynamoDB (no inbound rules)

Network ACLs (Stateless Subnet Protection):

• Public subnets: Allow inbound 443, 80; allow ephemeral ports (1024-65535) for responses
• Private app subnets: Allow all traffic from public subnets; deny direct internet inbound
• Private data subnets: Allow traffic only from app subnets; deny all internet traffic

AWS WAF Rules:

• AWS Managed Core Rule Set: SQL injection, XSS, LFI protection
• Rate-based rule: 2000 requests per 5 minutes per IP, temporary block for 10 minutes
• Geo-blocking: Block traffic from high-risk countries
• IP reputation list: Block known malicious IPs (updated daily)
• Size constraint: Block requests with body >8KB to prevent DoS
• Custom rule: Block requests without valid JWT token for authenticated endpoints

VPC Flow Logs:

• Enabled on VPC with ALL traffic capture
• Stored in S3 with 90-day retention
• Athena queries for security analysis and threat hunting

IAM Roles and Policies (Least Privilege)

Service Accounts (EKS Pod Identities):

• Each microservice has dedicated IAM role via IRSA (IAM Roles for Service Accounts)

• Booking service role: arn:aws:iam::ACCOUNT:role/booking-service-role

• Permissions: DynamoDB PutItem/GetItem on booking tables, SQS SendMessage to booking queue, SNS Publish to notification topic

• User service role: Limited to Cognito, DynamoDB user tables, S3 profile images bucket

Lambda Execution Roles:

• Separate role per Lambda function with minimal permissions
• Example: Image processor role has S3 GetObject (source bucket), S3 PutObject (processed bucket), no broad S3:* permissions

Human Access:

• No long-term access keys; SSO via AWS IAM Identity Center
• MFA mandatory for console access and sensitive operations
• Break-glass role for emergency access with CloudTrail alerts

Cross-Service Access:

• Aurora enhanced monitoring role: Limited to CloudWatch PutMetricData
• CodeBuild role: ECR push, S3 artifact access (build artifacts bucket only)

Data Encryption

At-Rest Encryption:

• Aurora PostgreSQL: Encrypted with customer-managed KMS key aurora-cmk, automatic key rotation enabled
• DynamoDB: Encryption at rest using AWS-managed keys (transparent), considering CMK for sensitive tables
• S3: Server-side encryption with SSE-KMS using bucket-specific CMK, enforced via bucket policy denying unencrypted uploads
• EBS volumes: All EKS node volumes encrypted with default KMS key
• ElastiCache: At-rest encryption enabled with CMK
• OpenSearch: Encryption at rest via KMS

In-Transit Encryption:

• All inter-service communication via TLS 1.3
• Aurora: SSL/TLS enforced via rds.force_ssl=1 parameter
• ElastiCache: TLS mode enabled on all connections
• Load balancers: HTTPS listeners with TLS 1.2+ only, SSL certificate from ACM
• Kafka (MSK): TLS encryption for broker communication and client connections

Field-Level Encryption:

• CloudFront field-level encryption for sensitive form data (credit cards, SSN)
• Application-level encryption for PII using AWS Encryption SDK before storage

Secrets Management

AWS Secrets Manager:

• Database credentials with automatic rotation every 30 days
• API keys for third-party services (payment gateways, email providers)
• JWT signing keys rotated quarterly
• VPC-hosted secret rotation Lambda functions

EKS Secrets:

• External Secrets Operator syncs from Secrets Manager to Kubernetes secrets
• Sealed Secrets for GitOps (secrets encrypted in Git, decrypted in cluster)
• Never commit plaintext secrets to repositories

Compliance Considerations

Standards:

• PCI-DSS Level 1 (payment card data handling)
• SOC 2 Type II (security, availability, confidentiality)
• GDPR compliance (EU user data protection)

Controls:

• Data residency: EU user data stored in eu-west-1 region only
• Right to erasure: Automated data deletion workflow
• Audit logging: All data access logged to CloudTrail (3-year retention)
• Encryption: All data encrypted at rest and in transit
• Access controls: MFA, least privilege, regular access reviews

DDoS Protection Strategy

AWS Shield Advanced:

• Layer 3/4 DDoS protection with 24/7 DRT (DDoS Response Team) access
• Cost protection against infrastructure scaling during attacks
• Real-time attack notifications via SNS

Application Layer Protection:

• WAF rate limiting and bot detection
• CloudFront geo-blocking and origin shield
• Auto-scaling to absorb volumetric attacks (cost implications monitored)

Monitoring:

• CloudWatch metrics for anomalous traffic patterns
• GuardDuty findings for reconnaissance and DDoS attempts
• Automated alarms trigger incident response runbooks ***

6. Well-Architected Framework Alignment

Operational Excellence

Infrastructure as Code: All infrastructure provisioned via Terraform with GitOps workflow; changes peer-reviewed before merge; immutable infrastructure pattern

Monitoring & Observability: CloudWatch dashboards for 50+ metrics, Grafana for application-level insights, X-Ray for distributed tracing with service maps; alerting via PagerDuty with on-call rotation

Automation: CI/CD pipeline fully automated from commit to production; automated scaling policies; self-healing with health checks and pod restarts; chaos engineering with LitmusChaos for resilience testing

Runbooks & Playbooks: Documented incident response procedures for common scenarios (DB failover, cache invalidation, traffic spike); quarterly disaster recovery drills

Security

Identity & Access Management: IAM roles with least privilege; IRSA for pod-level permissions; MFA enforced; no long-term credentials; audit logs retained 3 years

Detective Controls: GuardDuty for threat detection; Security Hub for compliance posture (CIS Benchmarks); VPC Flow Logs analyzed for anomalies; CloudTrail for API auditing

Infrastructure Protection: Multi-layer defense (WAF, Shield, Security Groups, NACLs); private subnets for data tier; bastion host with session manager for admin access; regular vulnerability scanning with AWS Inspector

Data Protection: Encryption at rest (KMS CMK) and in transit (TLS 1.3); secrets rotation every 30 days; field-level encryption for PII; backup encryption; data classification (public, internal, confidential, restricted)

Incident Response: Automated playbooks for common incidents; isolation procedures for compromised instances; forensic capabilities with EBS snapshots and memory dumps

Reliability

Fault Isolation: Multi-AZ architecture with 3 AZs; Aurora failover <30s; stateless application design; bulkheads between services prevent cascading failures

Change Management: Blue-green deployments with traffic shifting; automated rollback on error rate >1%; canary releases for high-risk changes; feature flags for gradual rollout

Failure Handling: Exponential backoff with jitter for retries; circuit breakers (Hystrix pattern) prevent cascading failures; graceful degradation (serve cached results when DB unavailable); timeout budgets on all network calls

Backup Strategy: Aurora PITR (35 days), DynamoDB PITR (35 days), EKS Velero backups, S3 versioning with cross-region replication; tested restore procedures quarterly

Self-Healing: EKS pod restarts, ALB health checks, Lambda automatic retries, Aurora automatic failover, auto-scaling based on health metrics

Performance Efficiency

Right-Sizing: Graviton2 instances (r6g, c6g) for 20% better price-performance; right-sized databases based on CloudWatch metrics; Lambda memory optimization for cost/performance balance

Caching Strategy: Multi-tier caching (CloudFront edge, ElastiCache L2, DynamoDB DAX L3); cache hit ratio >85%; appropriate TTLs per data freshness requirements

CDN Usage: CloudFront with 450+ edge locations; origin shield reduces origin load; static asset optimization (Gzip, Brotli compression); image optimization (WebP format, lazy loading)

Database Optimization: Read replicas for read-heavy workloads; connection pooling (PgBouncer) to handle 10K+ connections; query optimization with EXPLAIN ANALYZE; database indexes on frequently queried columns

Asynchronous Processing: Event-driven architecture with Kafka/EventBridge; SQS for decoupling; Lambda for background jobs; batch processing for reports

Cost Optimization

**Resourc