MACROMEDIA COLDFUSION 4.5-ADMINISTRING COLDFUSION..., Руководство пользователя

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132 Administering ColdFusion Server
operating system to manage the additional processor and is not available to help scale
the application servers.
It is important to note that application servers can only hope to scale relative to
resources when the resource changes affect the constraining resources. For example,
adding processor resources to an application server that is constrained by network
bandwidth will provide, at best, minor performance improvements. When discussing
linear scalability relative to server resources, it is implied that it is relative to the
constraining server resources.
Understanding linear scalability in relation to your site’s performance is important
because it not only affects your application design and construction but also indirectly
related concerns, such as capital equipment budgets.
Load management
Load management refers to the method by which simultaneous user requests are
distributed and balanced among multiple servers (Web, CFS, DBMS, file, and search
servers). Effectively balancing load across your servers ensures that they do not
become overloaded and eventually unavailable.
There are several different methods that you can use to achieve load management:
•
hardware-based solutions
•
software-based solutions, including round-robin Internet DNS or third-party
clustering packages
•
hardware and software combinations
Each option has its own distinct merits.
Most load balancing solutions today manage traffic based on IP packet flow. This
approach effectively handles non-application-centric sites. However, to effectively
manage ColdFusion application traffic, it is important to implement a mechanism that
monitors and balances load based on specific ColdFusion application load.
ColdFusion relies on a leading software-based clustering technology, ClusterCATS, to
ensure that the ColdFusion Server (CFS), the Web server, and other servers on which
your ColdFusion application depends remain highly available.
ClusterCATS is an important run-time component of your ColdFusion applications.
Only ClusterCATS can manage Web server traffic based on ColdFusion application
load.
See “Techniques for Creating Scalable & Highly Available Sites” on page 149 to learn
more about different hardware and software load management solutions.
Issues Affecting Successful Scalability Implementations
Achieving scalable Web servers is not a trivial task. There are various solutions to pick
from, setup and configuration tasks to understand and perform, and many delicate