mod_cluster boasts the following advantages over other httpd-based load balancers:
- Dynamic configuration of httpd workers:
Traditional httpd-based load balancers require explicit configuration of the workers available to a proxy. In mod_cluster, the bulk of the proxy’s configuration resides on the application servers. The set of proxies to which an application server will communicate is determined either by a static list or using dynamic discovery via the advertise mechanism. The application server relays lifecycle events (e.g. server startup/shutdown) to the proxies allowing them to effectively auto-configure themselves. Notably, the graceful shutdown of a server will not result in a fail over response by a proxy, as is the case with traditional httpd-based load balancers.
- Server-side load balance factor calculation
In contrast with traditional httpd-based load balancers, mod_cluster uses load balance factors calculated and provided by the application servers, rather than computing these in the proxy. Consequently, mod_cluster offers a more robust and accurate set of load metrics than is available from the proxy.
- Fine grained web-app lifecycle control
Traditional httpd-based load balancers do not handle web application undeployments particularly well. From the proxy’s perspective requests to an undeployed web application are indistinguishable from a request for an non-existent resource, and will result in 404 errors.… Read the rest