Our API, web UI and monitoring agent postbacks are routed through different IPs depending on your location, internet traffic conditions and maintenance events. As such, we don't advertise a single IP.
If you need to whitelist for your firewall, we recommend whitelisting your account URL in the form of ACCOUNTNAME.agent.serverdensity.io which will always resolve to the correct IP. However, if you need a specific static IP then please contact us and we'll be able to provide you with the details.
Our remote monitoring locations for availability monitoring have separate IPs, which are detailed in another document.