Keepalived

Keepalived is an open-source software project that provides high availability for network services by coordinating virtual IP addresses and load balancing on Linux systems. It works with Linux Virtual Server (LVS) to enable failover of VIPs and automated management of real servers, helping to minimize downtime in front-end services.

The core of keepalived is a daemon that reads a configuration file (keepalived.conf) to define VRRP instances, virtual IPs, and LVS real servers. It supports VRRP versions 2 and 3, both IPv4 and IPv6, and provides health checks through built-in simple tests, external scripts, or other monitoring mechanisms. When a health check or state change occurs, keepalived can trigger notify scripts to adjust system behavior or update LVS rules accordingly.

Operationally, keepalived is often deployed in conjunction with LVS to provide a highly available frontend VIP. In a typical setup, multiple nodes share a virtual IP via VRRP; one node acts as the master and holds the VIP, while others are backups. Node priority determines the master; if the master fails, a backup node takes over the VIP, and LVS rules are updated to restore service availability. The system uses VRRP heartbeat and kept-alives to coordinate failover with minimal disruption.

Use cases include providing HA for web front ends, API services, or other front-facing components that require a stable VIP and a scalable load-balancing layer. Keepalived is used in data centers and cloud environments to improve resiliency and automate failover processes. It is licensed under the GPL and actively maintained by the open-source community.