As the J2EE platform has matured, it has opened up the opportunity to deploy commodity servers in networked cluster configurations for scaling of Web services and Web applications at the Web tier. These commodity servers, interconnected through commodity LAN hardware, can provide cost-effective clustering solutions. The last piece of the clustering puzzle is in the software. In this seriesSing Li examines three open source software substrates that can enable high-impact Web tier clustering, beginning with JavaGroups.