In this case I believe @Chad_Wachs solution is likely the best course of action for right now.
As @simon mentioned, the Sonar instance never really touches the portal directly. The customer portal basically acts as a front-end GUI that just requests data from the Sonar instance using the API to retrieve customer account information and update account details.
If we were to update the customer portal code to have some type of polling functionality, if the customer portal server ever went down, there would be no way for it to poll or alert us that something was wrong since it’s down.
The only way this would work would be adding a new feature to Sonar v1 for the instance to talk with the portal server (our development team is focusing all efforts at the moment on getting V2 ready for everyone).
With all that being said, using something like the Uptime Robot is going to be the best solution in the meantime to achieve this desired functionality.