L4 and L7 Load Balancer

OSI Layer

1. Application
2. Presentation
3. Session
   • Above 3 layers can be grouped as one. Emits data such as HTTP, etc
   • PDU (Protocol data unit): Data
4. Transport
   • PDU: Segment
   • Contains Port Addresses to route to services and application (port 4500, etc)
   • TCP/UDP
5. Network
   • PDU: Packet
   • IP (IPv4 / IPv6)
   • Contains addresses in terms of IP Addresses
6. Data link
   • PDU: Frame
   • Physical network card. Has MAC addresses
7. Physical
   • Layer where data flows (optical, etc)

TCP/IP

• Application layer
• Transport layer
• Inter-network layer
• Network Access

Types of load balancer

1. Application load balancer (L7) Working with the application layer protocols such as HTTP. Routes HTTP requests based on path, http method, headers, cookies, etc. Example: Nginx (reverse proxy), AWS ALB
2. Network load balancer (L4) Works at network layer, routes TCP/UDP packets. Routes based on IP addresses. Example: AWS NLB