AWS Architecture: Scenario-Based Questions
7. How would you design a highly available web application architecture on AWS?
High availability (HA) ensures that your application remains accessible even if individual components fail. On AWS, this is typically achieved through multi-AZ, autoscaling, and decoupled services.
🏗️ Recommended Architecture Components
- Route 53: DNS failover with health checks for routing traffic to healthy endpoints.
- Elastic Load Balancer (ALB): Distributes traffic across multiple EC2 instances or containers in different Availability Zones.
- EC2 Auto Scaling Group: Launches instances across multiple AZs with health check replacements and scaling policies.
- RDS Multi-AZ: Synchronous standby in another AZ for database high availability.
- S3 + CloudFront: For static content distribution with global edge caching.
- Elasticache or DynamoDB: For highly available caching or NoSQL database needs.
⚙️ Design Characteristics
- Stateless Application: Store session data in ElastiCache or DynamoDB, not on EC2.
- Multi-AZ Distribution: Deploy compute and database layers across at least two AZs.
- Health Checks: Use application-level health checks to trigger failovers.
- Auto Recovery: Enable EC2 recovery or use Lambda for custom recovery logic.
🧪 Testing and Validation
- Simulate AZ failure using manual instance termination or network ACL blocking.
- Use
chaos engineeringtools like AWS Fault Injection Simulator or Gremlin. - Track metrics using CloudWatch alarms and dashboards for SLA compliance.
✅ Best Practices
- Use Infrastructure as Code (IaC) to automate consistent HA deployments (Terraform, CloudFormation).
- Perform regular failover drills and backup testing.
- Configure budgets and cost alerts — HA architectures can incur higher costs.
🚫 Common Mistakes
- Only using a single AZ (e.g., one EC2 or RDS instance).
- Hardcoding IPs or AZ-specific configs in application logic.
- Ignoring regional service limits or throttling behavior under load.
📌 Real-World Insight
High availability is often tested during traffic spikes or outages. Teams that bake HA into their cloud architecture from day one see improved uptime, customer satisfaction, and operational resilience.