System Architecture

The architecture of the Web Application Hosting architecture according to the flow of the numbers indicated respectively in the Figure 4.

1. Domain Name Server (DNS) – A user agent (or user) sends a request to a specified URL. The domain portion of the URL is resolved into an IP address via the Domain Name Service (DNS). This IP address may actually be the IP address of a CDN server, load-balancer, firewall, or proxy service in-front of the actual web application server that will satisfy the request.

2. The CDN server determines if any of the requested content is in the CDN storage network. If the CDN server cannot satisfy the request then the request is sent to the firewall.

3. If the CDN server is able to satisfy the request leveraging content in closest proximity to the user, then the CDN responds to the request by returning that content. The user’s browser retrieves and displays the returned content.

4. Firewall - The firewall evaluates the packets that form the request and allows those packets to continue forward to the load balancer if they meet the rules of the firewall. Typical rules might only pass incoming HTTP and HTTPS packets destined for ports 80 and 443. Firewalls often have two sets of rules, one for traffic from outside the firewall and one for traffic within the firewall. Generally, DNS resolution for internal requests is typically done using a private DNS Server rather than a public DNS server.

5. Load Balancers – The load balancer sends the request to a specific Web application server in a pool of web application servers. The decision is made using a random or ‘round robin’ algorithm, or some other method. For example, it might pick the server currently doing the least amount of work (least load). If the packet is associated with a web-session, the load-balancer may direct the message to the server that most recently handled a request in the same session (stickiness). Load balancers can direct requests by processing sophisticated rules, using systems and business policies, current and historic performance, as well as resource usage and availability in the underlying VMs or systems.

6. Web Application Servers – The web application server returns a resource (normally some form of web content) based on the user’s request. Based on the request the web server retrieves the static content by accessing the file system or invokes a program or service to generate dynamic requested content

7. Before any processing is done, the web application server may invoke the User Directory to authenticate the user and validate permission rights to perform the request. Typically this is done as a part of a login process, which establishes a session used for a series of requests.

8. The Web application server determines if the request can be satisfied by a local cache and file repository. If so the appropriate content and associated data is returned to the user through the firewall (see 10). If application logic must be invoked (by the application server) then retrieval of data from files, databases (see 9), web-services, sensors, and other sources of data as well as programmatic generation of new data or information may be required.

9. Databases –the web application server may need to access a database to query some data in order to generate the requested response.

10. When the web application server completes its tasks, the resulting content is delivered back through the firewall which passes the content to the user’s browser.