Elastic Load Balancer

Types of ELB

Application Load Balancer (Layer 7)
- Allows you to route to multiple instances in a Target Group (aka Backend Pool in Azure)
- Supports HTTP/2 and websocket
- Route based on the path in the URL, hostname, query strings, and headers
- Extra headers added by ALB
  - x-forwarded-for
  - x-forwarded-proto
  - x-forwarded-port
- ALB has a WAF capability that can be enabled
Network Load Balancer (Layer 4)
- High performance, millions of requests per second, and less latency ~100 ms
- NLB has one static IP address per AZ, and supports assigning an Elastic IP
- Not compatibly with the free tier
Gateway Load Balancer (Layer 3)
- Use cases: Send all traffic to a firewall, IDS, IPS, etc.
- Supports the GENEVE protocol on port udp/6081

Same client is forwarded to the same instance, rather than spreading traffic amongst all instances
Supported by the ALB and NLB
Cookie is set on the client with has an expiration date you control
- Cookies:
  - Two types of cookie are supported:
    - Application Based Cookie:
      - Custom cookie:
        
        Generated by the target
        
        Can include any custom attributes required by the application
        
        The cookie name must be specified individually per target group
        
        You cannot use AWSALB, AWSALBAPP, or AWSALBTG. These are all reserved by AWS
      - Application Cookie:
        
        Generated by the LB itself
        
        Cookie will be AWSALBAPP
    - Duration-based Cookie
      - Cookie is generated by the load balancer itself
      - Cookie name is AWSALB for ALB

Each load balancer instance distributes traffic evenly across all registered instances in all AZ
For the ALB, cross-zone load balancing can be enabled/disabled at the target group level. It is enabled by default and there are no additional charges
Can be enabled for NLB and GLB, but additional charges will apply. It is disabled by default.