> For the complete documentation index, see [llms.txt](https://huy312100.gitbook.io/software-development/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://huy312100.gitbook.io/software-development/cloud-service/aws/certificate/clf-c02/cloud-technology-and-services/elb-and-asg/elb.md).

# ELB

Elastic Load Balancing

### What is load balancing?

• Load balancers are servers that forward internet traffic to multiple servers (EC2 Instances) downstream.

<figure><img src="https://1722711354-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2FwNXdoUkfmcozr29fRrfb%2Fuploads%2F9CT0Dbchflt7bbDoW1Tu%2FScreenshot%202023-12-04%20at%2012.54.16.png?alt=media&amp;token=74f58529-ac97-4952-858d-327659fa8e06" alt=""><figcaption></figcaption></figure>

### Why use a load balancer?

• Spread load across multiple downstream instances

• Expose a single point of access (DNS) to your application

• Seamlessly handle failures of downstream instances

• Do regular health checks on your instances

• Provide SSL termination (HTTPS) for your websites

• High availability across zones

### Why use an Elastic Load Balancer?

• An ELB (Elastic Load Balancer) is a managed load balancer

* AWS guarantees that it will be working
* AWS takes care of upgrades, maintenance, and high availability
* AWS provides only a few configuration knobs

• It costs less to set your own load balancer but it will be a lot more effort on your end (maintenance, integrations)

• 4 kinds of load balancers offered by AWS:

* Application Load Balancer (HTTP / HTTPS only) – Layer 7
* Network Load Balancer (ultra-high performance, allows for TCP) – Layer 4
* Gateway Load Balancer – Layer 3
* Classic Load Balancer (retired in 2023) – Layers 4 & 7

<figure><img src="https://1722711354-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2FwNXdoUkfmcozr29fRrfb%2Fuploads%2FqsAWIceNbBz5vqPZCJmV%2FScreenshot%202023-12-04%20at%2012.56.00.png?alt=media&amp;token=d79faa69-ea84-483b-be35-475824d0cd90" alt=""><figcaption></figcaption></figure>