Problem Scenario:

In a big projects they may have multiple environments, in each environment they may want to host their own set of codes in their respective application server which is installed in different machines. So these environments are accessed locally with different local IP Address. 

Figure 1.1 Simple Architecture

The IP address that we assigned to the servers are private IP address. The idea behind private IP address concept is very simple – certain IP address range would be dedicated to use for hosts on private network. 

•Note : These addresses would be no longer valid on the public internet. 

•Solution: Organizations can use technologies such as NAT ( Network Address Translator ) or Proxy Servers to connect their private networks to the public Internet. When these technologies are used a single IP address is enough to connect entire organization to the Internet. 
 

So now what we are going to do?

•So now we are going to use the second technique, put one proxy server in front and delegate these request. 

Figure 1.2: NAT Process

Network Structure with Web Server in Front:

When the Apache Web Server put in front of the mutiple Oracle Weblogic Servers, the client requests would be delegated across environments.

Figure 1.3 : Web Server in front of App Server

Where this NAT Process will happen ?

•This NAT process may happen inside the DNS,NAT Router, NAT Firewall and etc . Here consider that this process is happening inside the DNS. So now all environment dns entries are pointed to the apache httpd web server.  Then the apache httpd web server pass on the request to the respective Oracle Weblogic application server. 

Figure 1.4 : Redefined Architecture With DNS Server

Complete Architecture with ISP Provider:

1] Personal Computers (assigned with Private IP Address) connected with the wired/wireless Router(assigned with Private IP Address).
2] Wired/Wireless Router is straight away connected with the Internet Service Provider(ISP). Each ISP(ex:Airtel,Tikona) provider one's one or more Public IP address.
3] This Internet Service Provider converts the private IP addresses to a Single Public IP address that they own atlast.
4]  Using this Public IP address finally your personal computer connected to  the Internet.



I hope that this would give a complete overview of how web server,ISP,NAT works from client's perspective.Please let us know if you have any doubts regarding this.