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= How to use execute an application on the nodes =

=== Prerequisite ===

This feature is only available in NodeHandler v4 and above.

Before going through this tutorial, you should know the basics of writing and running an experiment script (see [wiki:Tutorial/HelloWorld here] and [wiki:Tutorial/HowtoWriteScripts here]).

You should also have installed a disk image with Node Agent v4 on the nodes of the testbed you are using (e.g. "baseline-7.11.ndz"). See [wiki:Tutorial/HowToImage "How to install a disk image"].

=== Goal ===

In this tutorial, you will learn a simple way to execute an application on the nodes of a testbed.
  
=== The tutorial experiment ===

This experiment is given in the attached script [attachment:tut_app_1.rb tut_app_1.rb]. 

This file contains extensive comments that should help you understand the different steps involved in running an application on the nodes of a testbed.

To run this example script, use the following command:

 {{{
  nodehandler tut_app_1
 }}}

(This assumes that you previously logged in to a testbed with its nodes having a disk image such as "baseline-7.11.ndz").

=== The Results ===

The experiment screen output should then look like [attachment:sb1_2007_11_19_23_19_08-Output.txt this]. And the experiment log file should look like  [attachment:sb1_2007_11_19_23_19_08.log this].

NOTE: tcpdump outputs its user message on STDERR and not STDOUT, thus when running this tutorial script, please ignore false error messages such as: "ERROR nodeApp: tcpdump: listening on ath0, link-type EN10MB (Ethernet), capture size 96 bytes"

=== More... ===

If you would like to use the same application but with different parameters (or with parameters that you would like to dynamically change during the course of the experiment), then you should consider using a "prototype" around your application, as explained in [wiki:HowTo/LaunchApp this other tutorial].