TechEazy Consulting

Posted on Oct 3

Scaling Spring Boot with Auto Scaling Group (ASG) + Elastic Load Balancer (ELB)

#aws #asg #elb #ai

Deploying a Spring Boot app on multiple EC2 instances with an Application Load Balancer (ALB) works great ✅
But what happens when traffic spikes? Or if one EC2 instance crashes?

👉 That’s where Auto Scaling Groups (ASG) step in.

By the end of this guide, you’ll know how to:

Create an AMI of your Spring Boot app
Build a Launch Template
Configure an Auto Scaling Group (ASG)
Integrate it with your Application Load Balancer (ALB)
Auto-scale your application 🚀

👉 Flow: Browser → ELB → ASG → EC2 Instances running Spring Boot

🔑 Pre-requisite

From the previous blog, you should already have:

✅ 2 EC2 instances with Spring Boot JAR deployed on port 8080

✅ Application Load Balancer (ALB) setup with a Target Group

📦 Step 1: Create an AMI (Golden Image)

We’ll use one existing EC2 as a base image (AMI).

Go to EC2 Dashboard → Instances
Select an EC2 instance where your Spring Boot app is running
From Actions → Image and Templates → Create Image
Name it: springboot-ami
Click Create AMI

⏳ Wait 8–10 minutes. This AMI will be the blueprint for new EC2s in the ASG.

📝 Step 2: Create a Launch Template

Launch Template = Recipe to spin up new EC2s.

Go to EC2 → Auto Scaling Groups → Create Auto Scaling Group
Under Launch Template, click Create new launch template
Fill details:

Name: springboot-template
AMI: Select My AMIs → springboot-ami
Instance type: t3.micro
Key Pair: Same as before
Security Group: Must allow 22 (SSH), 80 (HTTP), 8080 (Spring Boot)

Add User Data (to auto-start the app):

#!/bin/bash
cd /home/ubuntu
sudo nohup java -jar app.jar > app.log 2>&1 &

Click Create Launch Template ✅

⚙️ Step 3: Create Auto Scaling Group (ASG)

Back to Auto Scaling Group creation
Name: springboot-asg
Select the Launch Template you just created
Click Next

🌐 Step 4: Configure Network Settings

VPC → Default VPC
Subnets → Select available ones (where ALB exists)
Leave defaults → Next

🔗 Step 5: Integrate with Load Balancer

On Load Balancer settings:

Attach to existing Load Balancer
Select your Spring Boot Target Group (8080)
Enable ALB health checks for reliability

Click Next

📊 Step 6: Set Group Size & Scaling Policy

Define scaling behavior:

Desired capacity → 2 (start with 2 instances)
Minimum capacity → 1
Maximum capacity → 3

Add a scaling policy:

Policy type → Target tracking
Metric → ALB Request Count per Target
Target Group → springboot-tg
Target Value → 50 (scale out if >50 requests per instance)

✅ Step 7: Review & Create

Double-check everything
Click Create Auto Scaling Group

Your ASG is now active 🎉

🔍 Step 8: Verify Setup

Go to EC2 → Instances → You’ll see new instances launched by ASG
Open ELB → Target Group → Targets → Should show healthy instances
Try terminating one instance manually → ASG will auto-recreate it!

🧪 Step 9: Load Test Your Setup

To simulate traffic for 5 mins:

ab -n 1000 -c 50 http://<ALB_DNS_NAME>/api/adapt/welcome

(Using ApacheBench or any load testing tool)

🎯 ASG will launch new EC2s automatically if traffic increases.

🎯 Final Result

You’ve successfully:

✅ Created an AMI for your Spring Boot app

✅ Configured a Launch Template

✅ Built an Auto Scaling Group (ASG)

✅ Integrated ASG with your Load Balancer

✅ Enabled self-healing + scaling 🚀

Now your app can handle failures and traffic surges without manual effort 💪

✅ Next Steps 🚀

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