This figure shows three Oracle CEP application scenarios. The single-server domain scenario shows one host with an Oracle CEP application running on it processing an input event stream and producing output events. The high availability scenario shows a multi-server domain composed of Host 1 and Host 2. Host 1 is the primary and Host 2 is the secondary. An Oracle CEP application is deployed to the the deployment group shared by Host 1 and Host 2. An event input arrives at both Host 1 and Host 2 but only Host 1 (the primary) outputs events. The high availability and scalability scenario shows a multi-server domain composed of Host 1, Host 2, Host 3, and Host 4. All hosts share the same deployment group. Host 1 and Host 2 are contained by one ActiveActiveGroupBean notification group and Host 3 and Host 4 are contained by a second ActiveActiveGroupBean notification group. The Host 1 and Host 2 notification group is the primary and the Host 3 and Host 4 notification group is the secondary. An event input arrives at all of Host 1, Host 2, Host 3, and Host 4 but only the hosts in the primary notification group (Host1 and Host 2) output events.