Radware AppDirector – Dispatch Methods
When creating a farm within AppDirector, one of the decisions you must make is choosing with dispatch method your farm will use. According to Radware’s official documentation, the dispatch methods are the load balancing algorithms that determine how client requests are distributed among servers within the farm. In other words, it’s how the AppDirector decides on which server to send the traffic to. Different types of applications will require different types of dispatch methods to properly balance traffic across your servers.
A recent discovery showed that our AppDirectors were sending an abundance of traffic to our first web server. At the same time, our other servers weren’t receiving as much traffic, sometimes less than 1/4 the traffic web server 1 was seeing. With close to 40 applications configured like this, you can see how resources for web server 1 were being exhausted while the other web servers sat mostly idle. Utilizing Excel and information from the Application Server statistics (Performance –> Servers –> Application Server Statistics) we could graphically see that traffic was abundant on web server 1 but quickly tapering off for all the other web servers in the farm. This farm was set up with a dispatch method of “Least Amount of Traffic”.
Once I had this statistical information saved I proceeded to change the dispatch method to “Fewest Number of Users” as this farm was part of a larger webfarm servicing end users. After running the application for a month on the new dispatch method, I recorded the same Application Server statistics for this particular webfarm. As show below in the graph, the results were exactly what you’d want to see on a load balanced farm – even distribution across all servers.
As shown above, the dispatch method alone can make a considerable difference in the way AppDirector distributes traffic to back-end servers. The dispatch method “Least Amount of Traffic” would be better suited for a farm containing FTP servers as traffic is more important for this farm. A dispatch method of “Fewest Amount of Users” will be better suited for a webfarm where the number of users is the more important factor. Radware offers a number of different dispatch methods from basic Cyclic and Weighted Cyclic to more advanced options including SNMP based and Private Parameters, or in other words “load balancing by any parameter that your want” method.
Last but not least, research each method and choose the one that best matches your farm’s requirements. Use the Application Server statistics page to monitor activity and modify configurations to get the best performance and load balancing for each application.