System Design
Load Balancing
Layer 4 vs Layer 7

Layer 4 vs Layer 7

Layer 4 Load Balancing (Transport Layer):

Characteristics:

  • Operates at the transport layer of the OSI model (TCP/UDP).
  • Balances traffic based on IP address and port.
  • Does not inspect the content of the traffic.
  • Faster and more efficient since it involves less processing.

Use Cases:

  • High Performance: When you need to handle a high volume of traffic with minimal latency and overhead.
  • Simple Traffic: Suitable for simple traffic routing needs where content inspection is not required.
  • Protocol Agnostic: Works well for any protocol that uses TCP/UDP, such as HTTP, HTTPS, SMTP, etc.

Example Scenarios:

  • Load balancing for internal services where security and complex routing rules are not a concern.
  • Situations where speed and efficiency are paramount, such as in real-time systems or high-frequency trading platforms.

Layer 7 Load Balancing (Application Layer):

Characteristics:

  • Operates at the application layer of the OSI model.
  • Balances traffic based on content, such as HTTP headers, URLs, cookies, etc.
  • Can perform advanced routing, SSL termination, compression, and other application-specific functions.
  • More resource-intensive due to deeper packet inspection and processing.

Use Cases:

  • Content-Based Routing: When routing decisions need to be made based on the content of the request, such as directing requests to different servers based on URL paths or HTTP headers.
  • Security and Authentication: Can handle SSL termination, authentication, and other security measures.
  • Complex Applications: Ideal for web applications, APIs, and microservices where requests need to be intelligently routed based on their content.

Example Scenarios:

  • Load balancing for web applications where different types of requests (e.g., static vs. dynamic content) need to be routed to different servers.
  • APIs where different versions or endpoints need to be directed to different backend services.
  • Microservices architectures where requests may need to be routed to specific services based on headers or request paths.
Load Balancing Algorithms