keepalived

keepalived has been primarily developed as a means to provide high availability for LVS. It does this via health checks of protocols and services, and informs the kernel in case of failure (or if it becomes available again), and it uses a version of the VRRP to handle failover for the LVS director. (VRRP is an open standard based on Cisco's HSRP)

-It runs as a user-space program

-It checks multiple layers of the TCP stack (i.e., based on the OSI 7 layer model). It does checks at the IP level, tcp level, transport dialogue layer (5), and application layer.


"Keepalived implements a framework based on three family checks : Layer3, Layer4 & Layer5/7. This framework gives the daemon the ability of checking a LVS server pool states. When one of the server of the LVS server pool is down, keepalived informs the linux kernel via a setsockopt call to remove this server entry from the LVS topology. In addition keepalived implements an independent VRRPv2 stack to handle director failover. So in short keepalived is a userspace daemon for LVS cluster nodes healthchecks and LVS directors failover."