What is the 'X-Forwarded-For' header?
Updated Apr 28, 2026
Short answer
An HTTP header used to identify the originating IP address of a client connecting through an LB or proxy.
Deep explanation
Mid-level load balancing involves optimization and protocol handling. SSL Offloading is a huge win for application performance. However, architects must decide between SSL Termination (decrypt at LB) and SSL Passthrough (decrypt at server) based on security requirements.
Real-world example
An e-commerce site terminating SSL at a Cloud Load Balancer to perform URL-based routing to 'Checkout' vs 'Catalog' services.
Common mistakes
- Relying on DNS Round Robin for high availability without a low TTL, leading to 15-minute outages when a server dies.
Follow-up questions
- What is SNI (Server Name Indication)?