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1.2. haproxy

HAProxy offers load balanced services to HTTP and TCP-based services, such as Internet-connected services and web-based applications. Depending on the load balancer scheduling algorithm chosen, haproxy is able to process several events on thousands of connections across a pool of multiple real servers acting as one virtual server. The scheduler determines the volume of connections and either assigns them equally in non-weighted schedules or given higher connection volume to servers that can handle higher capacity in weighted algorithms.
HAProxy allows users to define several proxy services, and performs load balancing services of the traffic for the proxies. Proxies are made up of a frontend system and one or more back-end systems. The front-end system defines the IP address (the VIP) and port on which the proxy listens, as well as the back-end systems to use for a particular proxy.
The back-end system is a pool of real servers, and defines the load balancing algorithm.
HAProxy performs load-balancing management on layer 7, or the Application layer. In most cases, administrators deploy HAProxy for HTTP-based load balancing, such as production web applications, for which high availability infrastructure is a necessary part of business continuity.