acassen/keepalived

Keepalived is a Linux system tool that addresses two related problems in server infrastructure: distributing incoming network traffic across multiple servers (load balancing), and making sure services stay available even when individual servers fail (high availability). For load balancing, it works with a Linux kernel feature called IPVS, which operates at the network layer to route incoming connections to one of several backend servers. Keepalived monitors those servers' health and automatically removes any that stop responding from the pool, then adds them back once they recover. For high availability, it uses a protocol called VRRP, which stands for Virtual Router Redundancy Protocol. The short version: multiple machines can share a single virtual IP address. If the machine currently holding that address fails, another machine in the group takes over the address within seconds, so external systems connecting to that IP see no interruption. This is commonly used to prevent a single machine from being a point of failure for a network. Keepalived also implements a protocol called BFD (Bidirectional Forwarding Detection) to detect network path failures faster than standard keepalive timers would allow. This speeds up the transition when a failover event needs to happen. The three components, load balancing, VRRP failover, and BFD detection, can each be used independently or together depending on the need. The project is written in C and is free software. Building from source requires autoconf, automake, and a few libraries, the repository includes an INSTALL file with details. An OpenSSL linking exception is included in the license to allow distribution with the OpenSSL Toolkit.