Keepalived

Keepalived solves two problems that go together in production Linux infrastructure: spreading traffic across servers and surviving the loss of one of them. For the first it drives the kernel's IPVS module to do Layer 4 load balancing; for the second it speaks VRRP, so a floating virtual IP moves to a standby node the instant the active one fails.

The two halves reinforce each other. Health checkers pull dead backends out of the IPVS pool automatically, while BFD detects link failure fast enough to trigger failover before clients notice. You can run the load-balancing and high-availability frameworks separately or wire them together, and hooks into the VRRP state machine let you react to transitions.

Written in C and maintained by Alexandre Cassen, Keepalived builds from source and runs locally on Linux with no hosted dependencies. GPL-2.0 licensed, with an OpenSSL Toolkit exception.