Building applications that stay online during failures is a critical skill for any cloud engineer. In this hands-on project from the AWS Academy Cloud Architecting programme, I redesigned a simple, single-instance setup into a fault-tolerant, highly available (HA) architecture running across multiple AWS Availability Zones.
This post breaks down the core components, how they work together, and what I learned along the way.
✅ What I Built
The goal was to transform a basic application into a multi-tier, multi-AZ architecture capable of surviving instance or Availability Zone failures.
The final environment included:
- VPC with public & private subnets
- Application Load Balancer (ALB) using two AZs
- Auto Scaling Group running EC2 instances across private subnets
- Amazon RDS (Multi-AZ) MySQL database
- NAT Gateways for secure outbound access
- Security Groups forming a strict 3-tier model
- CloudWatch for health checks and monitoring
This setup follows AWS best practices for reliability and security.
✅ Key Architecture Components
1. Application Load Balancer (ALB)
The ALB distributes traffic evenly across instances and performs continuous health checks.
If an instance becomes unhealthy, the ALB automatically routes traffic to healthy ones.
2. EC2 Auto Scaling Group
I created an AMI of the base web server and used it in a launch template.
The ASG maintains two instances at all times and replaces failed ones automatically — creating a self-healing system.
3. RDS Multi-AZ
Amazon RDS was upgraded to a Multi-AZ setup to provide automated failover.
If the primary database fails, traffic is redirected to a standby instance seamlessly.
4. Networking & Security
The architecture uses:
- Public subnets → Load Balancer
- Private subnets → EC2 application servers
- Private DB subnets → RDS instance
- NAT Gateways → Secure outbound traffic
Security groups enforce strict “layer-to-layer” communication:
- ALB → App layer
- App layer → DB layer
✅ Testing High Availability
The most exciting part was intentionally terminating one of the EC2 instances to simulate a failure.
Here’s what happened:
✔️ The ALB stopped routing traffic to the failed instance
✔️ The application stayed online with zero downtime
✔️ Auto Scaling launched a replacement automatically
This confirmed the architecture was functioning exactly as a real HA system should.
✅ What I Learned
- How to design for failure, resilience, and redundancy
- Importance of Multi-AZ deployments
- How Auto Scaling + ALB creates a self-healing system
- Building secure VPC environments with tiered security groups
- Using CloudWatch for monitoring and health checks
- Applying AWS Well-Architected Framework best practices
✅ Final Thoughts
This project showed me how enterprise-grade cloud systems are designed — not just to run, but to keep running even when things break.
I’m excited to keep building more AWS and DevOps projects that focus on reliability, automation, and scalability.
If you're also learning AWS or working on cloud architecture, I’d love to connect!
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