The following figure shows an example of how you can implement an application over multiple WebSphere Application Server deployment manager cells.
The example application runs simultaneously in two cells, each hosted on a different physical machine (Machines A and B). Load Balancer (known as Network Dispatcher in earlier releases) is used to distribute incoming HTTP requests between the two cells, presenting a single image of the application to clients. A backup Load Balancer node provides failover support.
Installing enterprise applications on the cluster in each deployment manager node ensures that identical versions of the application run in each cluster member. However, you administer each cell independently. Each cell has its own set of XML configuration files.
You can also run a different version of the application in each cell cluster. Because the cells are isolated from one another, you can also run different versions of the WebSphere Application Server software in each cell. For example, you can have a Version 5 cell and a Version 4 domain interoperating in your network.
Typical use
Topologies that incorporate more than one cell have the following advantages:
You can bring the new application or revision online in one cell, and test it in a live situation while other cells continue to handle client requests with the production version of the application.
You can bring the new version into production, and test it in a live situation without interrupting service.
You can take each cell offline to upgrade it, without interrupting the application.
If an unforeseen problem occurs with the new software, using multiple cells can prevent an outage to an entire site. You can also rollback to a previous software version more quickly. You can handle hardware and software upgrades on a cell-by-cell basis during off-peak hours.
Using multiple cells has several drawbacks: