Project 2 - A CDN

Due Thursday, April 10, 2008

For this project, you will develop a content delivery network (CDN) to deliver books on behalf of your booksite. Your server will maintain a list of all registered mirror sites and will redirect users to an appropriate mirror for download. The CDN will be responsible for replicating new content at all mirror sites. New mirrors may join at any time, and existing mirrors may leave at any time. Your program will build a tree of nodes and deliver content appropriately.

Functionality

The Main Site

The main server will provide all of the functionality described in Project 1, with the following additions:

Links to download content will refer to an appropriate mirror site, if one exists. You may use a simple round robin algorithm for distributing load among the mirrors.
The server will maintain a database of all mirror sites and the content that each has acknowledged receiving.
The server will serve as the source or root of the content delivery tree. When new content is added to the database, the server will POST the content to all of its children, attaching a timestamp (or sequence number) to each update.

Mirror Sites

The mirror sites are responsible for the following:

Mirrors serve txt and zip files as described in Project 1.
When a mirror comes online, it first registers itself with the main server and then recursively traverses the delivery tree to find an appropriate place to join.
Mirrors are responsible for ensuring that their parent remains live. If a parent fails to respond to a refresh message, a mirror must rejoin the tree.
A mirror must unregister its parent if it discovers that the parent has failed.
If a mirror receives a content POST from its parent, it is responsible for POSTing the given content to its children.
A mirror must send an acknowledgement to the server when new content is received. If a mirror receives content with a sequence number (timestamp) higher than expected, the mirror must request the missing content from its parent, or from the main server. Content should be added to the local mirror database in order of timestamp. If content is received out of order, it should be buffered until all previous updates are received.

This functionality is achieved by implementing the following interface. Your mirrors should all implement the same interface and should be able to interoperate.

Supported By	URI	Method	Response	Description
Main	/admin/register?ip={addr}&port={port}	GET	204 No Content/409 Conflict	Register a new mirror site with IP address addr listening at port port. The server must maintain a database of all mirror sites. Status 204 is returned if the register was successful. Status 409 is returned if the client cannot be registered (e.g., it is already registered).
Main	/admin/unregister?ip={addr}&port={port}	GET	204 No Content/409 Conflict	Unregister an existing mirror site with IP address addr listening at port port. Note that a mirror may unregister a mirror other than itself, for example if it discovers that its parent mirror has failed. Status 204 is returned if the unregister was successful. Status 409 is returned if the client cannot be unregistered (e.g., if it is not registered).
Main and Mirror	/admin/children	GET	200 OK <ResultList> <Child ip="addr" port="port"/> <Child ip="addr" port="port"/> </ResultList>	Retrieve a list of all a node's children.
Main and Mirror	/admin/refresh	GET	204 No Content	A response to a refresh request indicates to the requester that the responder has not failed. Status 204 is returned if the server receives the message.
Main and Mirror	/admin/join?ip={addr}&port={port}	GET	204 No Content/409 Conflict	Join as new child of the server with IP address addr listening at port port. Status 204 is returned if the join was successful. Status 409 is returned if the new child cannot be added (e.g., the child list of the server is already full).
Main	/admin/content?timestamp={num}	GET	200 OK Content of zip file	Retrieve the content with timestamp num. The main server is responsible for maintaining all back content and serving it to clients when requested.
Mirror	/admin/content?timestamp={num}	POST	204 No Content/409 Conflict.	Send content with timestamp num to child server.
Main	/admin/ack?ip={addr}&port={port}&timestamp={num}	GET	204 No Content/409 Conflict	An acknowledgement that the client with IP addr listening at port port has received message with timestamp num.

Other Tips

The number of children allowed will be a configurable parameter.

Due 5:30PM - Thursday, April 10, 2008

Complete and submit your working code. Place a copy of your source code and a readme in the submit directory /home/submit/cs682-s08/username.

Note: No portion of your code may be copied from any other source including another text book, a web page, or another student (current or former). You must provide citations for any sources you have used in designing and implementing your program.

Sami Rollins