AWS/aws-scalable-webapp-alb/AWS-SCALABLE-WEBAPP-ALB-README.md

🚀 AWS Scalable Web Application — ALB + ASG

A production-grade, self-healing web application deployed on AWS using an Application Load Balancer, Auto Scaling Group, and EC2 across multiple Availability Zones. Mimics how platforms like Heroku / Railway manage scalable deployments automatically.

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📸 Screenshots

All build screenshots are available in the /images folder, numbered 1 through 81 in chronological build order.

Key screenshots inline:

App Running via ALB DNS

App served through the Application Load Balancer DNS — no direct EC2 IP

Target Group — Both Instances Healthy in different AZ's

Both EC2 instances passing health checks across two Availability Zones

Auto Scaling Group — Instance Management after deleting

ASG maintaining desired capacity across ap-south-1a and ap-south-1b after terminating an ec2 machine to check for auto healing

AWS Notification -Subscription email

Confirmed notification subscription

CloudWatch Monitoring Dashboard

Real-time metrics — CPU, request count, response time, instance count

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🏗️ Architecture

Internet
    │
    ▼
Internet Gateway (scalable-webapp-igw)
    │
    ▼
┌─────────────────────────────────────────────────────────┐
│  VPC: scalable-webapp-vpc (10.0.0.0/16)                 │
│                                                         │
│  ┌──────────────────┐     ┌──────────────────┐          │
│  │ public-subnet-1a │     │ public-subnet-1b │          │
│  │  10.0.1.0/24     │     │  10.0.2.0/24     │          │
│  └──────────────────┘     └──────────────────┘          │
│            │                        │                   │
│            ▼                        ▼                   │
│   Application Load Balancer (webapp-alb)                │
│            │  HTTP :80 Listener                         │
│            ▼                                            │
│   Target Group (webapp-target-group)                    │
│    ├──▶ EC2 t3.micro — ap-south-1a  ✓ healthy           │
│    └──▶ EC2 t3.micro — ap-south-1b  ✓ healthy           │
│              ▲                                          │
│    Auto Scaling Group (webapp-asg)                      │
│    min: 1 │ desired: 2 │ max: 4                         │
│    CPU > 50% → scale out                                │
│    CPU < 30% → scale in                                 │
│              │                                          │
│    Launch Template (webapp-launch-template)             │
│    Amazon Linux 2023 + nginx                            │
└─────────────────────────────────────────────────────────┘

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⚙️ AWS Services Used

Service	Purpose
VPC	Isolated network with public subnets across 2 AZs
EC2	Compute — runs nginx web server
Application Load Balancer	Distributes traffic, health checks, single DNS entry
Auto Scaling Group	Automatically adds/removes instances based on CPU
Launch Template	Blueprint for identical EC2 instances
IAM Role	EC2 permissions for S3 and CloudWatch
CloudWatch	Metrics dashboard + CPU alarm via SNS email
Security Groups	Layered firewall — ALB faces internet, EC2 accepts ALB only

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🔐 Security Design

Internet → alb-sg (HTTP 0.0.0.0/0)
                ↓
           ec2-sg (HTTP from alb-sg ONLY)

EC2 instances are not directly reachable from the internet. All public traffic flows through the ALB only. This is a standard production security pattern.

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📦 Infrastructure Summary

VPC & Networking

Resource	Value
VPC CIDR	10.0.0.0/16
Public Subnet 1	10.0.1.0/24 — ap-south-1a
Public Subnet 2	10.0.2.0/24 — ap-south-1b
Internet Gateway	Attached to VPC
Route Table	0.0.0.0/0 → IGW

Compute

Resource	Value
AMI	Amazon Linux 2023
Instance Type	t3.micro
Web Server	nginx
Deployment	User data script on launch

Auto Scaling

Setting	Value
Minimum	1
Desired	2
Maximum	4
Scale-out trigger	CPU > 50%
Scale-in trigger	CPU < 30%

Monitoring

Resource	Value
Dashboard	webapp-monitoring
Alarm	webapp-high-cpu — triggers at 70%
Notification	SNS email alert

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🛠️ Build Phases

Phase	What was built
1 — Networking	VPC, subnets, IGW, route table, security groups
2 — Compute	Launch template, IAM role, test EC2, nginx + web app
3 — Auto Scaling	ASG with target tracking scaling policy
4 — Load Balancer	ALB, target group, listener, ASG integration
5 — Monitoring	CloudWatch dashboard, CPU alarm, SNS notification

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💡 Key Cloud Concepts Demonstrated

• High Availability — workload spread across 2 Availability Zones
• Horizontal Scaling — ASG adds instances under load, removes them when idle
• Self-healing Infrastructure — failed instances are automatically replaced by ASG
• Security Layering — EC2 not exposed directly, traffic flows ALB → EC2 only
• Infrastructure as a Blueprint — Launch Templates ensure every instance is identical
• Observability — CloudWatch dashboard + proactive alerting via SNS

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🧹 Cleanup

To avoid AWS charges after testing:

1. Delete Auto Scaling Group (this terminates all EC2 instances)
2. Delete Application Load Balancer
3. Delete Target Group
4. Delete Launch Template
5. Delete CloudWatch Alarms and Dashboard
6. Delete VPC (also removes subnets, IGW, route tables, security groups)
7. Delete IAM Role ec2-webapp-role
8. Delete SNS Topic webapp-cpu-alert

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📁 Repository Structure

aws-scalable-webapp-alb/
├── index.html          # Web app deployed on EC2 via nginx
├── README.md           # This file
└── images/             # All build screenshots (1–70, in chronological order)

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Learning Journey

Built as part of a hands-on AWS Cloud & DevOps learning journey.