How Keepalived Ensures High Availability in Web Server Clusters
This article explains how Keepalived automatically monitors web servers at the IP, TCP, and application layers, removes unhealthy nodes, and reintegrates them once recovered, thereby maintaining high availability and reducing manual maintenance in complex server clusters.
As system architectures evolve, the number and complexity of servers increase, making monitoring essential for maintaining high availability.
Keepalived provides automatic high‑availability protection by continuously checking server health and removing or reintegrating nodes without manual intervention.
How Keepalived Works
When monitoring web servers, Keepalived evaluates the status at three levels:
IP layer : It pings the target server; if the IP is unresponsive, the server is marked as failed and removed from the pool.
TCP layer : It checks the service port (e.g., port 80 for HTTP); if the port is closed, the server is considered failed.
Application layer : It runs user‑defined checks on the application process; if the process does not meet the expected criteria, the server is excluded.
Once a previously failed server recovers, Keepalived automatically adds it back to the cluster, ensuring continuous service availability.
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