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System Architecture

High Availability Cloud Architecture

Overview

This FinTech platform is designed for 99.99% uptime with automatic failover and disaster recovery capabilities.

Architecture Components

1. Load Balancing Layer

Purpose: Distribute traffic across multiple application servers

Implementation Options:

  • AWS: Application Load Balancer (ALB) with multi-AZ
  • Azure: Application Gateway with Availability Zones
  • GCP: Cloud Load Balancing

Features:

  • Health checks for automatic failover
  • SSL/TLS termination
  • Session affinity (sticky sessions)
  • Geographic routing

2. Application Layer (Multi-AZ)

Deployment Strategy:

Region: us-east-1 (Primary)
├── Availability Zone 1 (us-east-1a)
│   └── App Server Pool (Auto-scaling: 2-10 instances)
├── Availability Zone 2 (us-east-1b)
│   └── App Server Pool (Auto-scaling: 2-10 instances)
└── Availability Zone 3 (us-east-1c)
    └── App Server Pool (Auto-scaling: 2-10 instances)

Auto-Scaling Configuration:

  • Min Instances: 2 per AZ (6 total minimum)
  • Max Instances: 10 per AZ (30 total maximum)
  • Scaling Triggers:
    • CPU utilization > 70%
    • Memory utilization > 80%
    • Request count > 1000/min per instance
    • Response time > 500ms

3. Database Layer (High Availability)

Primary Database Setup:

  • Primary DB: Multi-AZ deployment (automatic failover)
  • Read Replicas: 2 replicas in different AZs
  • Backup: Automated daily backups with 30-day retention

Database Replication:

Primary DB (us-east-1a)
├── Read Replica 1 (us-east-1b) - Synchronous
├── Read Replica 2 (us-east-1c) - Synchronous
└── Backup Replica (us-west-2) - Asynchronous (DR)

Failover Strategy:

  • RPO (Recovery Point Objective): < 5 minutes
  • RTO (Recovery Time Objective): < 2 minutes
  • Automatic failover with zero data loss

4. Caching Layer

Redis Cluster:

  • Multi-AZ Redis cluster for session management
  • Cache for frequently accessed data
  • Rate limiting and throttling

5. Security Layer

Components:

  • WAF (Web Application Firewall): Protection against common attacks
  • DDoS Protection: Cloud-native DDoS mitigation
  • API Gateway: Rate limiting, authentication, request validation

Disaster Recovery (DR)

Multi-Region Setup

Primary Region: us-east-1 (N. Virginia) DR Region: us-west-2 (Oregon)

DR Strategy:

  1. Continuous Replication: Database replication to DR region
  2. Automated Backups: Hourly snapshots to DR region
  3. Infrastructure as Code: Terraform/CloudFormation for quick DR region deployment
  4. Failover Process: Automated DNS failover (Route 53)

DR Metrics:

  • RPO: 1 hour (maximum data loss)
  • RTO: 15 minutes (time to restore service)

Network Architecture

VPC Design

VPC: 10.0.0.0/16
├── Public Subnet 1 (10.0.1.0/24) - AZ-1 (Load Balancer)
├── Public Subnet 2 (10.0.2.0/24) - AZ-2 (Load Balancer)
├── Private Subnet 1 (10.0.11.0/24) - AZ-1 (App Servers)
├── Private Subnet 2 (10.0.12.0/24) - AZ-2 (App Servers)
├── Private Subnet 3 (10.0.13.0/24) - AZ-3 (App Servers)
└── Database Subnet Group
    ├── DB Subnet 1 (10.0.21.0/24) - AZ-1
    ├── DB Subnet 2 (10.0.22.0/24) - AZ-2
    └── DB Subnet 3 (10.0.23.0/24) - AZ-3

Security Groups

  • Load Balancer SG: Allow HTTPS (443) from internet
  • App Server SG: Allow HTTP (80) from Load Balancer SG only
  • Database SG: Allow PostgreSQL (5432) from App Server SG only

Monitoring & Observability

CloudWatch / Azure Monitor / GCP Monitoring

Key Metrics:

  • Application performance (response time, error rate)
  • Infrastructure metrics (CPU, memory, disk, network)
  • Database performance (connections, query time, replication lag)
  • Business metrics (transactions per second, user activity)

Logging

  • Application Logs: Centralized logging (CloudWatch Logs / Log Analytics)
  • Access Logs: All API requests logged with user context
  • Audit Logs: All data access and modifications (POPIA requirement)
  • Security Logs: Authentication attempts, authorization failures

Alerting

  • Critical Alerts: PagerDuty integration for 24/7 on-call
  • Warning Alerts: Email/Slack notifications
  • Alert Conditions:
    • High error rate (> 1%)
    • High latency (> 1 second p95)
    • Database replication lag (> 30 seconds)
    • Disk space < 20%
    • Failed health checks

Cost Optimization

  • Reserved Instances: For baseline capacity (1-2 year terms)
  • Spot Instances: For non-critical workloads
  • Auto-Scaling: Scale down during low-traffic periods
  • S3 Lifecycle Policies: Move old logs to Glacier after 90 days

Infrastructure as Code

  • Terraform: Infrastructure provisioning
  • Ansible: Configuration management
  • GitOps: Infrastructure changes via Git