The point is that according to your information different non-routable network addresses (loopback address 127.0.0.1, 192.168.x.x and 10.0.2.15) are used. Normally, those non-routable network addresses can't talk to an other (non-routable) network, other than with an addition to the routing table on every device that hosts an application (described nicely in the picture as 'virtual router'). In order for this to work, you need to know exactly where which application resides before or after a firewall on each required device.