Purpose

 The main puropse of TULIP Central Reflector is to proxy the TULIP queries to PlanetLab's Scriptroute Service. It may also be extended to issue all queries.  This decision will be related to speed of execution and security among other things. The PlanetLab Scriptroute service provides a cookie which works for a single IP address only. So in this way all the requests will be issued from the Central reflector and the responses will be sent back to the TULIP JNLP Client.

Implementation 

 The TULIP Central reflector will be a CGI Script (reflector.cgi) deployed at SLAC. The TULIP client will issue a single request and the Reflector will go ahead and probe all the landmarks in that region*\[1\] and return the results to the TULIP Client. Probing the target site from more vantage points may give us a better estimate of its location.

Requirements

• Should fetch sites.txt or have a local copy of sites.txt, what changes should be made to sites.txt ?
  • A new parameter should be added to sites.txt to include teir0 or teir1. Also the region of tier1 sites needs to be specified in sites.txt
• A separate thread should be used for each landmark and Semaphores should be used for locking, so that data from different threads should not inter-mix.
• There should be a limit on the number of threads that can be launched at a time (say 10).
• Should there be extra logging on the reflector or can we rely on the standard web logs which will log each query including time stamp, the client name.  What else it logs depends on whether the rewuest is Get or a Post.
• Where are the results parsed, could be in the reflector or in the Java client. In the client distributes the parsing load, reduces the load on the reflector, simplifies the CGI script.
• What should happen if a landmark responds with a bad data. ( Should it process the error or send the raw data back?). Since there will be some anomalies I suspect the reflector will need to return the full response and anyhow needs to inform the user, so I suspect initially the clinet will process the response and spot errors etc.) Also if the client parses the result it will probably be easily able to spot problems.
• Special consideration for security as the script ultimately has to be deployed at SLAC ( Perl taint option, warning oprion, special open method etc)
• Need to agree on a common format for the exchange of data.
•  

 After discussing with Yee and Booker it was seen that forks may be too complicated. The version of Perl at SLAC did not support threading. Also the security people will not allow forks running inside a CGI-script. So I had to come up with an alternative. The solution to this problem was to use Asyncronous IO.  A buch of requests could be send to the landmarks without waiting for he response.  The  LWP::Parallel library provides all this functionality.  It supports asyncronous IO. Currently it is not installed  so I am using a local version  in my home directory.  Ultimately this module has to be installed on the production server.

  I have implemented most of the functionality. The script is running fine. Now I will have to take measures to make the script more secure so that it could not be used as a platform to launch DDOS attacks. Also I need to incorporate some error messges in the script.
 

Sample Scripts

traceroute.pl: This script has been written with special security considerations so it will help in implementing reflector.cgi

topology.pm: This is a multi-threaded script written by Yee so this will help understand the threading issues in perl which are a bit complex.