Monitoring two application servers behind a firewall

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http://serverfault.com – I want to monitor that our Tomcat application servers is up and running. The application is not hosted in-house, but at a managed hosting provider. I do not have direct access to the application servers, but I can access them through a login-server. What is the simplest way to send an HTTP request to see if the Tomcat application servers is up? I already have a monitor system in-house (sensu), but this system does not have direct access to the Tomcat servers either. It can only be accessed through the login-server. +---------------+ +------ (HowTos)