The Linux Virtual Server (LVS) load balancers can send requests to predefined clusters and make parallel services of the cluster to appear as a virtual service on a single IP address. Scalability of the system is achieved by transparently adding or removing nodes in the cluster. High availability is provided by detecting node or daemon failures and reconfiguring the system appropriately.
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Keepalived is a routing software which is written in pure ANSI/ISO C.It provides simple and robust facilities to the Linux based system and infrastructure, for load balancing and high-availability. Keepalive consists of VRRP ( Virtual Router Redundancy Protocol ) implementations to manage virtual routers via virtual interfaces, and health check facility to determine whether a service is up and operational. If a service fails a significant number of health checks, the Keepalived will direct a virtual router over to a secondary node. Keepalived is very useful when combined with the Linux Virtual Server.
For more information on Keepalived, see the Keepalived user guide.
IPVS (Internet Protocol Virtual Server) implements transport-layer load balancing inside the Linux kernel's so called Layer-4 switching. IPVS runs as a load balancer at the front, of a cluster of real servers, and it directs requests from the TCP ( Transmission Control Protocol)/UDP (User Datagram Protocol) based services to the real servers. It also make services of the real server to appear as a virtual service on a single IP address.