8.1 The Abilities

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What is meant by the three 'abilities' addressed by Microsoft Application Center Server? These are scalability, manageability, and availability.

8.1.1 Scalability

This is covered in more detail in Chapter 10, but in summary, scalability is the capacity for an application or Web site to cope with increasing numbers of, typically, concurrent users. Within applications, bottlenecks will often appear, as more users are added and the servers or components start to stress and choke due to the demand for data or resources. This will manifest itself in a Web site as slow response or generally poor performance. For the Web site administrator, this will manifest itself as a phone call from his or her boss!

There is an important difference between scalability and performance. Many applications are deemed to be high-performance (e.g., processing many transactions per second), but as soon as you add extra users the application will slow. I have has seen cases of applications where increasing the users from 5 to 10 would destroy any level of performance. Although 10 users does not seem to be many, when users are selecting or updating large amounts of data the volume of database locks can increase dramatically, as can the requirement to serve up the all important session state information, often stored in the database as well.

8.1.2 Manageability

One 'ability' that Microsoft generally excels at is manageability. It has done a good job of bringing toolsets that make complex server-based products easier to use than in the past. The strangely named 'wizards' in many Microsoft products make setting up server applications a case of pointing and clicking, so many of the previously difficult or time-consuming tasks are now semiautomatic. That said, there are many cases when a wizard will run out of steam and only the intervention of an experienced administrator can save the day. Application Center uses the notion of a snap-in management tool with a set of wizards to manage and set up clusters and deploy content. In addition, it has a set of tools that support remote browser-based administration and, for the real diehards, a command line interface. An Application Center application is actually the content that a cluster will serve to site clients, and it will have all of the components and configuration settings needed to serve the content. A significant benefit of Application Center is that it keeps all of the disparate components of a Web site together in a single logical unit, which makes the deployment and subsequent management of a site much easier, including deployment across additional servers in the cluster. All of the associated logs of member servers in a cluster are automatically rolled into a single view of a cluster, making the process of clusterwide administration even easier.

8.1.3 Availability

This represents the last of our 'abilities.' There is little point in having a scalable, well-managed site if it is off-line and unavailable to users. To ensure the site is available, Application Center uses clusters of servers to remove any single point of failure. If any server member of a cluster should fail, the remaining members will pick up the workload and continue to make the site available. Monitoring tools within Application Center will detect failures and then trigger a range of responses as determined by the site administrator.

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