Elastic Load Balancer

Elastic Load Balancers (ELB) are AWS managed load balancers
AWS will take care of upgrades, maintenance and high availability of the load balancers
It is integrated with many AWS offerings such as:
- EC2, ASGs, Amazon ECS
- AWS Certificate Manager (ACM)
- CloudWatch
- Route 53
- AWS WAF, AWS Global Accelerator

Types of Load Balancers on AWS

AWS offers 4 kinds of load balancers:
- Classic Load Balancers (v1 - old generation) - CLB: supports HTTP, HTTPS, TCP, SSL (secure TCP)
- Application Load Balancers (v2 - new generation) - ALB: supports HTTP, HTTPS, WebSockets
- Network Load Balancer (v2 - new generation) - NLB : supports TCP, TLS, UDP
- Gateway Load Balancers - GWLB: operates at layer 3 (Network Layer) - IP Protocol

Rules on ALB are processed in order (default rule is going to be processed last)
Each rule has a supported action: forward, redirect, fixed-response
Rules can have conditions based on:
- host-header
- http-request-method
- path-pattern
- source-ip
- http-header
- query-string
Target Group Weighting:
- We can specify a weight for each Target Group on a single rule
- Allows us to control the distribution of the traffic to our application

Allows clients to communicate with the ELB using both IPv4 and IPv6 (dualstack URL)
Supported by both ALB and NLB
ALB and NLB can have mixed IPv4 and IPv6 targets, but only separate target groups
ELB dualstack ensures compatibility between clients and target IP versions:
- IPv4 clients will communicate with IPv4 targets
- IPv6 clients will communicate with IPv6 targets
- In case there are only IPv4 targets, the ELB automatically converts requests from IPv6 to IPv4