Besides a proper monitoring tool, every application should have application developed health check to verify the environment is up and for troubleshooting.
Really should have these in order of importance.
Application Up - Basic test to ensure application is working not going through the web server.
Load Balancer Health Check - Note here the sample code (to be provided) which minimizes load to the system.
Code Version - Version of code deployed. Actually for trouble-shooting with End Users suggest PC Financial at one point put a unique code at bottom footer.
Java Version - Obfuscated.
Server Name - Obfuscated.
Database Connectivity - Basic test to ensure connection works. Make sure to keep this very limited.
Key Services - Verifies key services are working.
Key Integration Points - Good example is verifying an external web service.