SharePoint 2010 Web front end and application server request execution path

I have a question about how the SharePoint 2010 handle a user request when the environment have for example one web front end and one application server.

Does the web front e开发者_Go百科nd just route the request to the application server and the application sever do the entire job then send the response back, or the web front end process the request locally and just ask the application server about specific service like excel for example.

And if the first answer is true does that mean that if my application server goes down and I have many web front end, all the system goes down (single point of failure). I will appreciate your response.

No, the second answer is true. The regular request are taken care of by the WFE, the app server handles backend calculations for the services. But if you have a page that requires data from the app server in real time (Excel Services WP maybe), these web parts will give out an error