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1. The Web Grid Manager presents a Web interface that shows information of the whole Grid and present simple buttons to operate the Tomcat instances.
   
2. The managing logic must be clearly separated from the Web interface logic, since later on, a Command-Line Grid Manager will be included, and will use the same managing logic.
   
3. The available commands for each instance are:
   • status: retrieves the status of a Tomcat instance through the corresponding Grid Agent
   • trigger-start: sends a start request to the Tomcat instance using the corresponding Grid Agent
   • trigger-stop: sends a stop request to the Tomcat instance using the corresponding Grid Agent
   • trigger-kill: sends a kill request to the Tomcat instance using the corresponding Grid Agent
     

4. Wiki Markup
   A simple configuration file lists all the machines and their instances so the Grid knows where each instance resides. \[This configuration file is probably in XML format\] \\

5. Grid Agents are installed on each machine and manage all instances in that machine pertaining to the Grid. Grid Agents receive commands from any manager and act accordingly. To manage the instances the Agents use:
   • Shell calls: start an instance, kill an instance.
   • JMX calls to retrieve instance live information.
   • JMX calls to change instance live values, and to request instance shutdown.
   • OS calls for any OS related need.
     
6. It's assumed that a port will be accessible from each Grid Manager to each machine where the Grid Agents are serving. The firewall, if present must allow active server-type sockets on that port.
   
7. Multiple Grids (and Grid Agents) can be running on the same set (or subset) of machines. If that's the case, Tomcat instances, and Grid Agents run on different ports for each grid. When multiple grids use the same machines they don't interfere with each other and can be operated simultaneously.
   
8. The status command shows the following information for each instance:
   • Machine
   • Service (a unique grid-wide name for each instance)
   • State
     
9. The state of an instance can be:

   • Wiki Markup
     *Active*: the instance OS process exists, the instance is serving requests, and it looks healthy \[enough\]. \\

   • Wiki Markup
     *Zoetic* \[for lack of a better word\]: the instance OS process exists, but the instance is unresponsive and it doesn't respond to requests for state. It's probably not serving any HTTP requests, does not look healthy, it may be starting, it may be shutting down, it may be overwhelmed. Who knows. \\

   • Stopped: the instance OS process does not exist, and therefore the instance is not operating at all.
     
   • Not Available: This is a pseudo state that the manager applications (web and cli) show when a Grid Agent does not respond to requests for status in a timely manner.
     
   • If possible it would be great to discern different sub cases of the Zoetic state, so to help the user to determine what's going on and tackle the case accordingly:
     • Starting: The Tomcat instance process exists, and the instance is starting. It's not yet serving HTTP requests.
       
     • Stopping: The Tomcat instance process exists, and the instance is stopping. It's no longer serving HTTP requests.
       
     • Unresponsive: The Tomcat instance process exists, but the instance health isn't good, it's not responding to HTTP requests, or it's overwhelmed. It's not even responding to requests for status.
       
     • On second thoughts, these extra states can actually be discerned today with the current version of Tomcat, since the Grid Agents know all the trigger commands each local instance has received and can deduce (or make up) the sub case. If the Grid Agent is restarted, some kind of persistence of its state might be needed to "remember" what was going on before the Grid Agent was shut down, so to make an educated guess.
       
10. Grid Agents communicate over unsecured TCP sockets, and assume communication security is enforced by the network architecture (segregated segments/VLans).
    
11. The "trigger"-type commands just deliver the corresponding signal to the instance's Grid Agent and returns right away, without waiting for the full operation to complete. It's kind of "fire and forget". The web user can keep on refreshing the the web interface to find out about the progress of the status of the Tomcat instances.
    

12. Wiki Markup
    Simple user name/password authentication is implemented to secure the Web interface. \[Maybe we'll need to provide more options\] \\

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