AWS Basics - Beginner's Guide to ELB

Elastic Load Balancers

A load balancer distributes network traffic across a group of servers.

A load balancer might send an incoming request to the server which is least busy, or might use a round-robin algorithm to forward requests to each server in turn.

Types of load balancers

Application Load Balancer

• Operates at OSI Layer 7
• Application aware
• Load balancing of HTTP and HTTPS traffic
• Supports advanced request routing to specific web servers based on the HTTP header

Network Load Balancer

• Operates at OSI Layer 4
• Most expensive AWS load balancer
• Used in production especially if we have latency as an issue
• Capable of handling millions of requests per second, maintaining ultra-low latencies
• Used for load balancing of TCP traffics where extreme performance is required

Classic Load Balancer

• Not recommended anymore
• Legacy
• Load balance HTTP/HTTPS applications using Layer 7 features
• Load balance applications relying on TCP protocols using strict Layer 4
• Support Layer 7 features such as X-Forwarded-For headers and sticky sessions (allows us to keep sending requests originating from the same session to the same web server)

Creating a load balancer

1. Create Load Balancer from EC2 Dashboard
2. Configure load balancer
3. Configure security settings
4. Configure security groups
5. Configure routing: create target group and add health checks
6. Register targets with existing EC2 instances
7. Review and create

X-Forwarded-For

The X-Forwarded-For header allows us to identify the IP address of the client connecting through a load balancer.

Common load balancer errors

• Error 504 Gateway timeout - if app stops responding

Revisiting the OSI - 7 layer model

This is a conceptual framework which describes the functions of a network.

Layers	Description
7 (application)	what the end user sees, HTTP, web browsers
6 (presentation)	data is in a usable format - encryption, ssh
5 (session)	maintains connections and sessions
4 (transport)	transmits data using protocols such as TCP and UDP
3 (network)	logically routes network packages based on IP addresses
2 (data link)	physically transmits data based on MAC addresses
1 (physical)	transmits bits and bytes over physical devices

Route53

Route53 is Amazon's DNS service.

Allows mapping domain names to

• EC2 instances
• Load Balancers
• S3 Buckets

Registering a domain name and mapping to a load balancer

Registering a domain name can take up to 3 days to complete. Once registered, it will automatically appear in the Hosted Zones.

1. Select Route53 from Services/Network and Content Delivery.
2. Click on Register Domain.
3. Choose a domain name and register.
4. On successful registration, domain name appears in Hosted Zones.
5. Select Hosted Zones and select your hosted zone.
6. Click on Create Record - Turn on alias -> select routing policy -> select record type -> select endpoint, region and load balancer to route traffic to.
7. Click Create Record to create the record under Hosted Zones.