AggreGate IoT Platform was designed with an unlimited scalability in mind. While communication with a million devices definitely requires multiple servers to get joined into a distributed installation, even a single AggreGate Server based on a single CPU server hardware can demonstrate the impressive performance figures.
of these events get passed through the whole event processing workflow and routed to the operator workstations or external systems
The number of devices serviced by a single server is only limited by the available server resources, mostly CPU power and RAM size. It will greatly vary depending on the number of device metrics, their polling/update period and storage settings, as well as the devices' event generation rate. A detailed server hardware selection guide is available here.
OEMs, VARs and system integrators designing AggreGate-based solutions should consider the performance optimization hints provided independently for each type of an "active" server object. Check the system documentation for details.