In my previous post, I explained how to create and use an Amazon EC2 instance to run applications in the AWS cloud. While EC2 gives you control over your servers, it requires manual effort to handle changes in traffic and workload.
As applications grow and traffic becomes unpredictable, managing capacity manually can be inefficient and costly. AWS Auto Scaling solves this by automatically adjusting the number of EC2 instances based on demand.
In the next section, we’ll walk through a step-by-step guide on how to set up AWS Auto Scaling from scratch.
What Is AWS Auto Scaling?
AWS Auto Scaling automatically adjusts the number of EC2 instances running in your application based on demand. When traffic increases, Auto Scaling adds more instances. When traffic decreases, it removes extra instances.
AWS Auto Scaling automatically increases or decreases the number of EC2 servers running your application based on traffic or usage.
More users → more servers added
Fewer users → extra servers removed
This keeps your application available while controlling costs.
Think of Auto Scaling like a security team at an event:
- When more people arrive, more guards are added
- When people leave, extra guards go home
- The event runs smoothly without waste
Moving forward, in a previous post, we created an Amazon EC2 instance to run an application. As we progress, we will build on that setup and extend it by configuring AWS Auto Scaling.
Setting Up AWS Auto Scaling (Step by Step)
Step 1: Confirm Your EC2 Instance Is Running
Before setting up Auto Scaling:
- Go to EC2 → Instances
- Ensure your EC2 instance created earlier is running
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Confirm it has:
- A working application
- A security group allowing required traffic (for example, HTTP on port 80)
This EC2 instance will be used as the base for Auto Scaling.
Step 2: Create an Auto Scaling Group
- Click Auto Scaling Groups
- Click Create Auto Scaling group
- Enter a name
- Select the launch template
- Click Next
Step 3: Choose Network Settings
- Select your VPC
- Choose at least two subnets
- Click Next
This improves availability.
Step 4 Attach a Load Balancer (Recommended)
- Choose Attach to a new load balancer
- Select Application Load Balancer
- Enable Health checks
This ensures traffic is shared and unhealthy instances are replaced.
Step 5: Set Capacity Limits
Define how many servers can run:
- Desired capacity: 1
- Minimum capacity: 1
- Maximum capacity: 3
Click Next.
Step 6: Configure Scaling Policy
This tells AWS when to scale.
- Choose Target tracking scaling
- Metric: Average CPU utilization
- Target value: 50%
AWS will now scale automatically.
Step 7: Review and Create
- Review your settings
- Click Create Auto Scaling group
Your EC2-based application is now fully scalable.
What Just Happened?
- You started with one EC2 instance
- Auto Scaling now launches identical EC2 instances when needed
- Extra instances are removed when traffic drops
User traffic reaches the Load Balancer → traffic is shared across EC2 instances → Auto Scaling monitors CPU usage → new instances are added when demand increases → unused instances are removed when demand drops.
When Should You Use Auto Scaling?
Use Auto Scaling when:
- Traffic is unpredictable
- You want high availability
- You want to reduce costs
- You don’t want to manage servers manually
Final Thoughts
AWS Auto Scaling helps your application stay online, responsive, and cost-efficient without manual effort. It works perfectly with EC2, Load Balancers, and Elastic Beanstalk, making it a core AWS service every beginner should understand.
Without Auto Scaling, a single EC2 instance can become overwhelmed or fail. By extending your EC2 setup with Auto Scaling, you ensure better performance, availability, and cost control.
Auto Scaling does not replace EC2—it builds on it to make your application scalable and reliable.
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