Closing thoughts on topologies

 

Regardless of which topology you decide to use, a best practice is to partition your production acceptance environment in exactly the same way as your production environment. This avoids surprises when deploying your application into production.

Another consideration, when practical for your application architecture, is to create a number of smaller appservers, rather than a single large one. This has at least two advantages:

  1. The plug-in configuration files can be smaller (less complexity of URIs), which leads to better startup performance and possibly to better execution performance.

  2. At least during the development phase, it takes less time to cycle a smaller appserver to pick up various configuration changes.

Of course, the benefits of creating multiple appservers in this manner must be carefully balanced against the increased complexity of doing so, and the potential increase in response time due to interprocess RMI/IIOP calls and network latency.

If, after looking at all the topologies, you are still wondering what would be the best possible topology, one possibility is illustrated in Figure 3-20.

Figure 3-20 One of the best possible topologies

This topology includes two of everything:

  1. Cells
  2. Database servers (two for each cell - you need to ensure data replication between these database servers)
  3. Application servers (two sets for each cluster)
  4. HTTP servers (two for each cell)
  5. HTTP dispatchers (WebSphere Load Balancer or a similar product)

Only the loss of an entire cell will normally be noticed by users. If this were to occur, the active HTTP sessions would be lost for half of the users, requiring that they log in again. Of course, performance would most likely be degraded in this case as well, but it would ensure continuous availability. In most cases, hardware or software upgrades would be handled on a cell-by-cell basis during non-peak hours. If customer satisfaction (performance, throughput, availability) is important for your Web site, then this would be the appropriate topology.

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