DFP Agent for WebSphere is an implementation of Cisco's Dynamic Feedback Protocol for WebSphere. It adds a DFP agent to the WebSphere runtime to allow it to report status information to a load balancer supporting that protocol. The code currently only supports reporting two discrete weights:

• 0 if the application server is not fully started or is stopping (i.e. if the HTTP port is not yet open or going to close).
• 1 if the application server is in state STARTED (i.e. if the HTTP port is open).

In a setup where a Cisco load balancer is put directly in front of a WebSphere cluster (without an IBM HTTP Server or other reverse proxy between them), this makes it possible to restart a WebSphere instance without loosing requests. This works because the load balancer is immediately aware that the WebSphere instance is going to stop.

The code could easily be extended to calculate weights dynamically, based on parameters such as the CPU load or the usage of the Web container thread pool.

The code was developed as a proof of concept and has been tested successfully. However, it has never been used in production. The design of the code is very clean and easily extensible (Actually it is somewhat over-engineered because it was originally expected that more than two DFP message types would need to be supported).

Feel free to clone the project and/or to contact the author if you think the code may be useful to you or you need additional information.

The code is licensed under the GNU Public License, version 2.

The project is an Eclipse plug-In project. Before importing it into Eclipse, create a target platform definition from the WebSphere runtime (Note that the project was developed using WAS 7.0, but it may be buildable using a more recent version) and select it as default. After importing the project, use "Export > Deployable plug-ins and fragments" to build the plug-in JAR.

To install the agent into WebSphere, drop the plug-in JAR into the plugins folder of the WebSphere installation. Then use the osgiCfgInit tool to refresh the OSGi caches (otherwise WebSphere may fail to load the plug-in). To enable the DFP agent, define a new port with name DFP_AGENT_ADDRESS and a suitable port number in the configuration(s) of the WebSphere application server(s) where the agent should run.

Note that each DFP agent instance will report the status of the local application server only. Therefore, a DFP agent needs to be configured on each application server to which the CSS directs HTTP traffic.

On the load balancer, use the dfp command to add each DFP agent configured on WebSphere. Choose a suitable timeout: this will determine how much time it will take the load balancer to detect that a server has crashed without properly closing the connection.

Then set the static weight of the services to zero. This is very important because the DFP agent is restarted together with the WebSphere instance and the load balancer will use the static weight if the DFP agent is not available. However, we want the effective weight to be non zero only if the WebSphere server is running and the HTTP port is open.

The DFP Agent developed by this project implements the subset of the Dynamic Feedback Protocol that is used by Cisco Content Service Switches (CSS). This includes the following message types:

• DFP Parameters (inbound)
• Preference Information (outbound)

The agent doesn't support the following message types:

• Server State: unfortunately CSS never sends Server State messages
• BindID Request, BindID Report and BindID Change Notify: CSS doesn't seem to make use of the Bind-ID concept

In addition, security is currently not supported.