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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