A large real-estate brokerage is exploring the option of adding a cost-effective __cpLocation based alert to their existing mobile application. The application ...

A large real-estate brokerage is exploring the option of adding a cost-effective __cpLocation based alert to their existing mobile application. The application backend infrastructure currently runs on AWS. Users who opt in to this service will receive alerts on their mobile device regarding real-estate otters in proximity to their __cpLocation. For the alerts to be relevant delivery time needs to be in the low minute count the existing mobile app has 5 million users across the US.
Which one of the following architectural suggestions would you make to the customer?