[yegle]

That only indicate the frontend of the service is up and potentially running. Being about to respond to ping and being able to serve HTTP request are two different things, and being able to serve HTTP request vs a fully functional website are two different things. Think about wrong SSL certification, wrong domain mapping between frontend/backend, broken JS/CSS etc.

[CloudNetworking]

This outage is a great example. I can ping Google Calendar servers and I get an HTTP response. SSL also works like a charm.

And yet everybody agrees it's down.