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AWS EC2 Auto Scaling: How to Build a Scalable Application Infrastructure

Learn how AWS EC2 Auto Scaling helps applications handle changing traffic by automatically adding or removing EC2 instances. This article explains the architecture, scaling process, and key AWS components in simple terms.

ISHWAR GOSAVI

Devops Enginner

AWS EC2 Auto Scaling: How to Build a Scalable Application Infrastructure

Modern applications can experience different levels of traffic throughout the day. If an application runs on only one EC2 instance, a sudden increase in traffic can cause high CPU usage, slow response times, or even application failure.
AWS provides EC2 Auto Scaling to solve this problem.

What is EC2 Auto Scaling?

Amazon EC2 Auto Scaling automatically adjusts the number of EC2 instances running your application based on demand.
For example:
  • Low traffic → fewer EC2 instances
  • High traffic → more EC2 instances
  • Traffic decreases → unnecessary instances are terminated
This helps maintain application performance while controlling infrastructure costs.

Basic Architecture

A typical architecture looks like this:
Internet
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v
Application Load Balancer
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+-------------------+
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v v
EC2 Instance EC2 Instance
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+---------+---------+
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v
Auto Scaling Group
The main components are:
  1. Application Load Balancer
  2. Auto Scaling Group
  3. Launch Template
  4. EC2 Instances
  5. CloudWatch

1. Launch Template

A Launch Template defines how new EC2 instances should be created.
It can contain:
  • AMI
  • Instance type
  • Security groups
  • Key pair
  • IAM role
  • User data
  • Storage configuration
When Auto Scaling needs another instance, it uses this template to launch it.

2. Auto Scaling Group

An Auto Scaling Group (ASG) manages the EC2 instances.
For example, we can configure:
  • Minimum instances: 2
  • Desired instances: 2
  • Maximum instances: 5
If traffic increases, the ASG can increase the number of instances from 2 to 5.
When traffic decreases, it can scale the instances back down.

3. Application Load Balancer

The Application Load Balancer distributes incoming requests across healthy EC2 instances.
For example:4. CloudWatch
Amazon CloudWatch can monitor metrics such as:
  • CPU utilization
  • Network traffic
  • Request count
  • Application performance
These metrics can be used to trigger scaling actions.
For example:
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CPU > 70%
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CloudWatch Alarm
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Auto Scaling Group
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Launch New EC2 Instance

Example Scaling Scenario

Suppose our application starts with two EC2 instances.
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Minimum = 2
Desired = 2
Maximum = 5
During normal traffic:
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Load Balancer
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EC2 EC2
Now suppose traffic suddenly increases.
CloudWatch detects high CPU utilization.
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CPU > 70%
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Scaling Policy
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New EC2 Instance
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Load Balancer distributes traffic
The infrastructure may now look like:
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Load Balancer
/ | \
v v v
EC2 EC2 EC2
If traffic increases further, Auto Scaling can launch additional instances up to the configured maximum.

Scale-In

Auto Scaling also works in the opposite direction.
When traffic decreases:
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5 EC2 Instances
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Lower traffic
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Auto Scaling
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3 EC2 Instances
This prevents us from paying for unnecessary EC2 instances.

Why Use Auto Scaling?

EC2 Auto Scaling provides several benefits:

High Availability

Running multiple instances reduces dependency on a single server.

Scalability

The infrastructure can automatically respond to changing traffic.

Cost Optimization

Instances can be removed when they are no longer required.

Fault Tolerance

If an instance fails, the Auto Scaling Group can replace it.

Example DevOps Architecture

For a DevOps-based application, EC2 Auto Scaling can be combined with other AWS and DevOps tools:
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Developer
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GitHub
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Jenkins
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Docker Image
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Amazon ECR
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EC2 Auto Scaling Group
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+-------------------+
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 EC2 Instance EC2 Instance
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+---------+---------+
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Application Load Balancer
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Users
Infrastructure can also be created using Terraform, allowing the AWS infrastructure to be managed as code.

Important Scaling Concepts

There are three important values in an Auto Scaling Group:

Minimum Capacity

The minimum number of instances that should always be running.

Desired Capacity

The number of instances the application normally starts with.

Maximum Capacity

The maximum number of instances that Auto Scaling can create.
For example:
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Minimum = 2
Desired = 2
Maximum = 5
This means the application will normally run with two instances but can automatically scale up to five.

Conclusion

AWS EC2 Auto Scaling is an important component for building reliable and scalable applications.
By combining:
  • EC2
  • Auto Scaling Groups
  • Application Load Balancer
  • CloudWatch
  • Launch Templates
we can build infrastructure that automatically responds to changing workloads.
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Users
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Application Load Balancer
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EC2 Instance EC2 Instance
# auto-scaling# aws-cloud9
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