The request flows through several stages. First it hits
the load balancer:

+--------------------+
| Load Balancer|
+--------------------+

Then it gets routed to one of the app servers, which
processes the request and queries the database:

+--------------------+     +--------------------+
| App Server   |---->| Database     |
+--------------------+     +--------------------+

Finally the response is sent back to the client.