Hello,
Any tool that is used would require configuration in order to allow a Automatic Failover to happen, there is no application that will work "automatically". You would need the tool to monitor the HealthCheck Servlet, and then perform an action to trigger the FailoverServlet upon getting a "NOT OK" response from the HealthCheck. Nimsoft Snap can easily be configured to monitor the health, but I believe additional adjustment of Nimsoft Snap is required in order for it to trigger the failover task.
For whatever tool that is used it should trigger the Failover task on its own once configured, assuming the product being used as the ability to perform the action.