# ELB

## ELB (Elastic Load Balancer)

Evenly distributes incoming web traffic across multiple EC2 instances in multiple availability zones.

* This increases fault tolerance of apps
* ELB detects unhealthy instances and routes traffic only to healthy instances.

![](/files/-MAPypKHr3mN5AjrRWUn)

### [Pricing](https://aws.amazon.com/elasticloadbalancing/pricing/)

**Free tier is NOT** available for ELB.

* How are you charged for using ELB
  * each hour or partial hour the load balancer is running
  * for each GB of data transferred through the load balancer

## Auto Scaling

A tool that can automate scale-in and scale-out of EC2 instances based on traffic demands.

* scaling **in and out** => adds and removes instances
* scaling **up and down** => adds additional resources like memory/disk to existing instances

#### Autoscaling groups

![](/files/-MAQ3imzLHNIERmdDb0x)

![](/files/-MAQ3ZPZNaUov2gFgBzI)

Auto scaling happens based on thresholds.

![](/files/-MAQ46MSFGVZRNVG3Exp)

#### Autoscaling components

* Launch configuration
  * EC2 template used when auto scaling needs to add an additional server to auto scaling group
* Auto scaling group
  * all the rules and settings that govern when EC2 server is automatically added or removed

### Pricing

Auto scaling is free to use.But you will be charged for resources that Auto Scaling provision (e.g. EC2 instances that go beyond Free Tier allotment)

#### How to create

* create launch configuration
* create auto scaling group using launch configuration


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