GT 4.0 WS MDS WebMDS: Developer's Guide

Table of Contents

1. Introduction
2. Before you begin
2.1. Feature summary
2.2. Tested platforms
2.3. Backward compatibility summary
2.4. Technology dependencies
2.5. Security considerations
3. Architecture and design overview
4. Public interface
5. Usage scenarios
5.1. Creating a new plugin
5.2. Changing format of output
6. Troubleshooting
7. Related Documentation

1. Introduction

WebMDS is a web-based interface for viewing formatted information about Grid resources. Information is collected via a plugin interface and then formatted using an XSLT transform.

2. Before you begin

2.1. Feature summary

Features new in release 4.0:

  • Extensible plugin interface to support various mechanisms to gather monitoring information and XSLT transforms.
  • Plugins to acquire monitoring information via resource property mechanisms.
  • Plugin to acquire XSLT transforms by reading from local files.

Other Supported Features

  • WebMDS is a new component, so all its features are "new in release 4.0".

Deprecated Features

  • None

2.2. Tested platforms

Tested Platforms for WebMDS:

  • The WebMDS server has only been tested with Tomcat version 5.0.28; it has been tested on RedHat Linux (i386) and, to a lesser extent, on Windows XP.
  • On the client side, WebMDS should be accessible from any web browser on any platform.

2.2.1. Installing WebMDS on Windows

Although the WebMDS server is not officially supported on non-Unix platforms, and no Windows installer exists for WebMDS, it is possible to run WebMDS on Windows. The following instructions describe how to install WebMDS on a Windows platform.

  1. Install Tomcat and set your CATALINA_HOME environment variable to the directory into which Tomcat was installed.
  2. Install the Globus Java WS-Core distribution from the Globus Toolkit download page. Set your GLOBUS_LOCATION environment variable to the directory into which you installed Globus Java WS-Core
  3. Check the ws-mds distribution out of the Globus CVS repository, using the globus_4_0_branch tag.

  4. Install the servicegroup package:

    cd c:\wherever\ws-mds\servicegroup\schema
ant deploy
cd ..\source
ant deploy

    where wherever is the directory into which you checked out the ws-mds sources.

  5. Install WebMDS:

    cd c:\wherever\ws-mds\webmds
ant deploy

  6. Create the webmds context file (this tells Tomcat where to find WebMDS): 

    %GLOBUS_LOCATION%\lib\webmds\bin\webmds-create-context-file %CATALINA_HOME%\conf\Catalina\localhost
  7. Restart Tomcat.

WebMDS can then be configured and used as described in the rest of the WebMDS documentation.

2.3. Backward compatibility summary

Protocol changes since GT version 3.2:

  • WebMDS did not exist in GT version 3.2.

API changes since GT version 3.2:

  • WebMDS did not exist in GT version 3.2.

Exception changes since GT version 3.2:

  • WebMDS did not exist in GT version 3.2.

Schema changes since GT version 3.2:

  • WebMDS did not exist in GT version 3.2.

2.4. Technology dependencies

WebMDS depends on the following GT components:

  • Java WS Core

WebMDS depends on the following 3rd party software:

2.5. Security considerations

By default, the WebMDS plugins distributed as part of the Toolkit do not use authentication credentials -- they retrieve information using anonymous SSL authentication or no authentication at all, and thus retrieve only publicly-available information.

The ResourcePropertyNodeSource and ResourcePropertyQueryNodeSource plugins can be configured either to allow users to specify what resources they want to query or to only allow users to query resources pre-configured by the web administrator. The standard WebMDS deployment allows users to specify the resources they want to query; to disallow this (for example, to ensure that people don't use your site's bandwidth to view information about some other site's services), remove the files $GLOBUS_LOCATION/lib/webmds/conf/openEndedRP and $GLOBUS_LOCATION/lib/webmds/conf/openEndedQuery.

3. Architecture and design overview

In a typical WebMDS transaction, a user uses a web browser to send an HTTP request, including some web form arguments, to a web server / servlet container. The web server invokes the WebMDS servlet, which uses the form arguments to determine what plugins to use to retrieve the requested XML data and the XSLT transform to apply to it. The WebMDS servlet passes arguments to the plugins, which then retrieve the appropriate data and XSLT transform. The WebMDS servlet applies the XSLT transformation to the XML data and returns the result to the web server, which sends it back to the client's web browser.

4. Public interface

The semantics and syntax of the APIs and WSDL for the component, along with descriptions of domain-specific structured interface data, can be found in the GT 4.0 Component Guide to Public Interfaces: WS MDS WebMDS.

5. Usage scenarios

There is no "client" programmatic interface to WebMDS; clients communicate using HTTP requests. The web form arguments recognized by WebMDS are documented in GT 4.0 WS MDS WebMDS: User's Guide.

5.1. Creating a new plugin

To create a new plugin to collect raw XML data, write a Java class that implements the WebmdsXmlSource or WebmdsNodeSource interface. These are documented in Section 1, “Semantics and syntax of APIs”. The FileXmlSource and NodeXmlSource classes distributed with WebMDS are examples of classes that implement WebmdsXmlSource; the ResourcePropertyNodeSource and ResourcePropertyQueryNodeSource classes distributed with WebMDS are examples of classes that implement the WebmdsNodeSource interface.

5.2. Changing format of output

To change the appearance of the output of WebMDS, create a new XSLT transform; see the W3C XSLT Documentation for more information.

6. Troubleshooting

Log information from WebMDS and any WebMDS plugins will be logged by the servlet container into which WebMDS has been deployed. In a vanilla Tomcat 5.0.28 distribution, this information will show up in the file $CATALINA_HOME/logs/catalina.out

7. Related Documentation

None available at this time.