Distributing traffic.
WHAT IT DOES
Distributes requests across several servers, and stops sending to unhealthy ones.
WHAT LAYER FOUR BALANCING IS
Distribution based on addresses and ports, without inspecting content.
What it provides: very high throughput and protocol independence.
WHAT LAYER SEVEN BALANCING IS
Distribution based on request content: path, hostname, headers.
What it provides: routing decisions, and manipulation of requests.
WHAT ALGORITHMS EXIST
Round robin Least connections Weighted variants Hashing, for consistency
WHAT LEAST CONNECTIONS SUITS
Backends where request duration varies.
WHAT HEALTH CHECKING DOES
Removes failing backends from rotation.
WHAT MAKES A GOOD HEALTH CHECK
It exercises the dependencies the service needs, not merely that the process is listening.
WHY
A server accepting connections while its database is unreachable is not healthy.
WHAT TO BE CAREFUL WITH
Health checks so heavy they cause load Checks so shallow they detect nothing All backends failing checks simultaneously
WHAT TO CONFIGURE
Graceful removal, allowing existing requests to complete.
WHAT TO MONITOR
Backend health, distribution, and response times per backend.
