Cloud Architecture

Design scalable, resilient, cost-effective cloud architectures using AWS, Azure, or GCP and cloud-native patterns.

When to Use This Skill

• Cloud migration planning
• New cloud application design
• Multi-cloud strategy
• Cost optimization
• Scalability requirements
• High availability needs
• Disaster recovery planning
• Cloud-native modernization

Core Concepts

1. AWS Well-Architected Framework

## 6 Pillars

**1. Operational Excellence**
- Infrastructure as Code (Terraform, CloudFormation)
- CI/CD automation
- Monitoring and logging
- Incident response

**2. Security**
- IAM with least privilege
- Encryption (at rest, in transit)
- Network security (Security Groups, NACLs)
- Compliance and auditing

**3. Reliability**
- Multi-AZ deployment
- Auto-scaling
- Backup and recovery
- Fault isolation

**4. Performance Efficiency**
- Right-sizing instances
- Auto-scaling policies
- Caching (CloudFront, ElastiCache)
- Database optimization

**5. Cost Optimization**
- Reserved Instances / Savings Plans
- Spot Instances
- S3 lifecycle policies
- Cost monitoring and alerts

**6. Sustainability**
- Efficient resource utilization
- Managed services
- Serverless adoption
- Region selection

2. Reference Architecture - 3-Tier Web App (AWS)

## AWS 3-Tier Architecture

**Tier 1: Presentation**
- Route 53 (DNS)
- CloudFront (CDN)
- S3 (static hosting)
- WAF (Web Application Firewall)

**Tier 2: Application**
- Application Load Balancer
- Auto Scaling Group (EC2 or ECS)
- Multiple Availability Zones
- Security Groups

**Tier 3: Data**
- RDS Multi-AZ (PostgreSQL)
- ElastiCache (Redis)
- S3 (file storage)

**Supporting Services:**
- VPC (network isolation)
- CloudWatch (monitoring)
- Systems Manager (configuration)
- Secrets Manager (credentials)
- SNS/SQS (messaging)

**Diagram:**

Internet ↓ Route 53 → CloudFront ↓ Application Load Balancer ↓ +---+---+---+ | EC2 | EC2 | EC2 | (Auto Scaling Group) +---+---+---+ ↓ ↓ RDS ElastiCache (Multi-AZ)

3. Cloud Migration Strategies (6 R's)

**1. Rehost ("Lift and Shift"):**
- Move as-is to cloud
- Fast migration
- No code changes
- Example: VM to EC2

**2. Replatform ("Lift, Tinker, and Shift"):**
- Minor optimizations
- Use managed services
- Example: Self-managed DB → RDS

**3. Refactor / Re-architect:**
- Redesign for cloud-native
- Microservices, serverless
- Highest benefit, most effort

**4. Repurchase:**
- Move to SaaS
- Example: Email server → Office 365

**5. Retain:**
- Keep on-premises (for now)
- Not ready for migration

**6. Retire:**
- Decommission unused applications

**Migration Plan:**

Phase 1 (Month 1-2): Low-risk apps (Rehost) Phase 2 (Month 3-4): Databases (Replatform to RDS) Phase 3 (Month 5-8): Core apps (Refactor gradually) Phase 4 (Month 9-12): Legacy apps (Evaluate retain/retire)

4. Multi-Cloud Strategy

## Multi-Cloud Architecture Patterns

**Best-of-Breed:**
- AWS: Compute (ECS/EKS)
- GCP: Data analytics (BigQuery)
- Azure: Enterprise integration (AD)

**Geographic Redundancy:**
- Primary: AWS us-east-1
- DR: Azure West Europe

**Vendor Diversification:**
- Avoid lock-in
- Negotiate better pricing
- Skills distribution

**Challenges:**
- Increased complexity
- Multiple billing systems
- Different tooling
- Network connectivity
- Cost tracking

**Tools:**
- Terraform (multi-cloud IaC)
- Kubernetes (portable orchestration)
- Prometheus (monitoring)
- Vault (secrets management)

Best Practices

1. Well-Architected Reviews - Regular assessments
2. Infrastructure as Code - Terraform, CloudFormation
3. Managed services first - Reduce operational overhead
4. Multi-AZ deployment - High availability
5. Auto-scaling - Handle traffic variations
6. Cost monitoring - Set budgets and alerts
7. Security by design - IAM, encryption, network security
8. Disaster recovery plan - Backup, failover, testing

Resources

• AWS Well-Architected: https://aws.amazon.com/architecture/well-architected
• Azure Well-Architected: https://docs.microsoft.com/azure/architecture/framework
• GCP Architecture Center: https://cloud.google.com/architecture
• Cloud Architecture Patterns: https://docs.microsoft.com/azure/architecture/patterns