Cloud Architecture: Scenario-Based Questions

High Availability (HA) ensures your system can operate continuously without failure for a long time. In cloud environments, HA relies on redundancy, fault tolerance, and smart distribution of resources.

🧱 Core Principles

• Redundancy: Duplicate critical components (e.g., multiple web servers, DB replicas).
• Failover: Automatic switching to backup systems during failure (e.g., multi-AZ DB failover).
• Load Balancing: Distribute requests evenly to avoid overloading any node.
• Health Checks: Continuously monitor component status and remove unhealthy ones.

🏗️ Cloud Design Patterns

• Deploy across multiple Availability Zones (AZs) within a region.
• Use managed services with built-in HA (e.g., RDS Multi-AZ, DynamoDB, Cloud Spanner).
• Design stateless services behind autoscaling groups and ALBs.
• Use regional or global load balancers (e.g., AWS ALB/ELB, GCP Load Balancer).

📦 Example Architecture

• Frontend in AWS behind an ALB with EC2 or Fargate instances in 2+ AZs.
• RDS or Aurora with Multi-AZ failover and read replicas.
• Redis or Memcached with replication and failover nodes.
• CI/CD to roll out updates gradually and avoid downtime.

🧰 Supporting Tools

• Route 53 / GCP Cloud DNS: For DNS-based failover across regions.
• Terraform: Codify HA setups with reusable modules.
• Monitoring: Use CloudWatch, Stackdriver, or Datadog to detect and alert on downtime.

✅ Best Practices

• Test failover regularly using chaos testing or blue/green deployments.
• Keep services loosely coupled and resilient to downstream outages.
• Use SLA-backed managed services where HA is mission-critical.

🚫 Common Pitfalls

• Single AZ deployments — vulnerable to outages or data center failures.
• Hard dependencies on stateful services that don’t replicate well.
• No clear RTO/RPO definitions — leading to surprise during failure.

📌 Real-World Insight

High availability is not just about “uptime.” It’s about designing failure into your architecture — assuming components will break, and preparing your system to recover automatically and gracefully.