1. A high availability planning and scheduling system, comprising: a plurality of high availability (HA) systems coupled to one or more external systems using a message bus, each HA system including: an HA server operable to receive and queue requests received from the external systems; and an advanced planning and scheduling (APS) engine operable to: receive a request from the HA server; process the request using planning information stored in memory of the HA system; modify the planning information according to the processing of the request; and generate a response to the external system from which the request originated; and a message manager operable to direct each request received from an external system to an appropriate HA system using the message bus.