Layer 4 load balancing operates at the transport layer of the OSI model, focusing on the IP address and port number to distribute traffic. It makes decisions based solely on the source and destination IP addresses and ports, without inspecting the content of the traffic. This type of load balancing is typically faster and less resource-intensive because it doesn't analyze the data packets. An example of Layer 4 load balancing is DNS load balancing, where requests are distributed to different servers based on the DNS query.
Layer 7 load balancing, on the other hand, operates at the application layer of the OSI model. It examines the content of the traffic, allowing for more intelligent routing decisions. This includes analyzing HTTP headers, cookies, and even the content of the requests to determine the best server to handle the request. Layer 7 load balancing can provide advanced features like session persistence, content-based routing, and SSL termination. An example is directing requests to different servers based on the URL path or the type of content requested.
For cloud-based solutions, Tencent Cloud offers services that support both Layer 4 and Layer 7 load balancing. Their Cloud Load Balancer service provides a highly available and scalable solution for distributing traffic across multiple servers, with capabilities to handle both types of load balancing needs.