AWS Auto Scaling.

AWS Auto Scaling is a service that automatically increases or decreases EC2 instances based on traffic and load.
It makes your application scalable, cost-efficient, and highly available.

Think of Auto Scaling like:

Adding or removing servers automatically when users increase or decrease.

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Why Auto Scaling is used

Auto Scaling is used to:

• Handle traffic spikes

• Avoid server overload

• Save cost

• Improve availability

• Run applications without manual intervention

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Where Auto Scaling is used

Auto Scaling is used in:

• Web applications

• E-commerce websites

• APIs

• SaaS platforms

• Production systems

• Microservices

• Cloud applications

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When to use Auto Scaling

Use Auto Scaling when:

• Traffic is unpredictable

• You want zero downtime

• You want automatic scaling

• You want high availability

• You want to pay only for what you use

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Core Components of Auto Scaling

1. Launch Template

This defines:

• AMI

• Instance type

• Key pair

• Security groups

• User data

It tells AWS how to create new EC2 instances.

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2. Auto Scaling Group (ASG)

This is a group of EC2 instances that:

• Increases

• Decreases

• Replaces unhealthy instances

You set:

• Minimum

• Desired

• Maximum number of instances

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3. Scaling Policies

These decide:

• When to add or remove EC2

Types:

• Target tracking

• Step scaling

• Simple scaling

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4. CloudWatch Metrics

ASG uses:

• CPU utilization

• Network

• Requests count
  to decide scaling.

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How Auto Scaling works

Traffic increases → CPU goes high
CloudWatch sends alarm
ASG launches new EC2
ELB starts sending traffic to new EC2

Traffic decreases → ASG terminates extra EC2

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Auto Scaling with Load Balancer

ASG is mostly used with:

• Application Load Balancer

So traffic is evenly distributed.

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Health Checks

Auto Scaling checks:

• EC2 status

• ELB health

If an instance fails:

• ASG deletes it

• New one is launched automatically

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Availability Zones

ASG can launch EC2 in:

• Multiple AZs

So if one AZ fails, others still run.

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Cost benefit

You pay only for:

• Running instances

When traffic drops, instances are removed.

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Real world example

E-commerce site
Morning: 2 servers
Sale time: 20 servers
Night: back to 2

All automatic.

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DevOps usage

Auto Scaling is used for:

• High availability

• CI/CD environments

• Blue-green deployment

• Disaster recovery

• Cost optimization

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Auto Scaling vs Load Balancer

Both are used together.

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Interview points

• Works with CloudWatch

• Uses Launch Template

• Supports ELB

• Automatic healing

• Multi AZ support