Previewing Windows .NET Servers
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Internet Information Services 6.0
Moving now to the application layer of the operating system, one component that underwent considerable changes with this release is the Internet Information Service (IIS), which is now available as IIS 6.0. As a security precaution, IIS, as well as other components of the server that were installed by default with Windows 2000, is now available as an optional component that can be installed during server configuration after the core installation process has completed. The majority of the changes focus on improving the performance and reliability of the server. In this article, we will only focus on the architectural changes and not the operational changes.
In IIS 5, there were two isolation options for Web applications running on the server. An
application could run as a process, thereby creating one process for each application
running on the system, or all of the applications could run as part of a separate process, conserving the amount of resources consumed by the Web server. This mode of operation is still available with IIS 6, but is not the default mode and needs to be set explicitly at the server level through the IIS MMC plug-in. Figure 2 shows the process structure of IIS running in IIS 5 isolation mode. In the example shown, one application is running as part of the main Web service process, using no isolation at all, and another one is set up to run as part of the single-pooled process called
Figure 2. Process structure of IIS when the server is configured to run in IIS 5 isolation mode.
IIS 6 introduces the concept of a worker process and a new isolation mode. A worker process is similar to a unique instance of
dllhost.exe that is used to host one or more applications or sites. Since more than one application can be assigned to run on a given worker process, IIS 6 uses the term "application pool" to refer to them. The main
inetinfo.exe process is now a separate, totally isolated process, with no applications running within its memory space. This increases the reliability of the Web server itself. In addition, the administrator can now control
how many worker processes are spawned and the assignment of applications to those
worker processes. This makes the configuration very flexible, in that the administrator can decide how to trade off isolation and reliability in exchange for the amount of system resources consumed by the Web applications. Figure 3 shows the process structure of IIS running in the new default isolation mode. The example shows that there are two worker processes configured, one running a single application and the second one running multiple applications.
Figure 3. Process structure of IIS when the server is configured to run in the new isolation mode.
You've probably noticed a third block in the figure, called a Web garden. When we introduced the term "worker process" earlier in this section, the explanation indicated that a single worker process forms an application pool to which Web applications and sites are assigned, but that is not always the case. When constructing an application pool, the administrator has the option to decide how many worker processes to assign to the pool. When two or more worker processes are configured as part of an application pool they form what is referred to as a Web garden. A Web garden allows an application to achieve higher scalability, since multiple processes are used to process requests on its behalf. A Web garden is like a Web farm (in that it aims to achieve higher scalability), but within the confines of a single server.
Figure 4 shows the new look of the MMC plug-in for
IIS. The tree control has a list of Web sites as before, but now it also includes a list of application pools. The example shown in the figure has four application pools configured, with the pool named "Default Application Pool" selected and expanded. Three applications have been assigned to the Default Application Pool, and the panel on the right shows the path associated with each of the applications assigned to this pool. Although we don't show this in the figure, while configuring an
application pool the administrator is given a number of choices that affect the lifecycle of the worker processes. The administrator can choose how often the worker processes should be refreshed, to ensure that they are not negatively impacted by the application (for example, they may be growing in
size due to memory leaks in the applications hosted within them); can decide how long a worker process should be idle before it is removed from the system; and can also configure the monitoring of the worker processes by the main
inetinfo.exe process, to ensure that they are restarted if there is a crash due
to an application error.
Figure 4. Illustrates the new look of the MMC plug-in for IIS.
Before we close the section on IIS, we must bring up another architectural change that was made to IIS 6 that should result in a considerable performance boost. If you pay close attention to figures 2 and 3, you will notice that IIS now communicates with a component that runs within the kernel. That component is called
http.sys, and as its name implies, it is responsible for handling and dispatching requests to the
Web server coming off of the network. By having this component be part of the kernel, if a request arrives for static content and that content is already cached in memory, the Web server can respond immediately to the request without having to make a context switch to user mode.
In addition to this important performance benefit, moving this component to the kernel totally isolates this basic Web server functionality from any application code running in user mode that could cause the Web server to crash. Each application pool created by the administrator has an associated queue in kernel mode. As requests enter the system, if they cannot be serviced immediately by the
they are dispatched to the appropriate kernel queue from where they are picked up for processing by one of the worker processes associated with that application pool.
Command Line Utilities
Another improvement in Windows .NET Server is the release of a large number of command line utilities for assisting with system management tasks. We are not going to discuss every single one of them here, but we'll review some of the more interesting ones.
logman utility allows you to manage, from the command line, a performance counter collection task. By passing options, you can specify whether a new collection is started or whether an existing one is stopped or deleted. For
example, the command:
Logman create counter daily_perf_log -b 7/27/2000 13:00:00 -e 7/27/2000 15:00:00 -r -v mmddhhmm -c "\Processor(_Total)\% Processor Time" "\Memory\Available bytes" -si 00:15 -o "c:\perflogs\daily_log"
will cause the system monitor to collect the two specified metrics starting and ending at the given times with a sampling interval of 15 seconds, and store the output in the file
daily_log. The example shown above comes straight
from the page for the
logman utility from the much-enhanced help facility. The
relog utility can be used to resample existing log files and save selected metrics to a new log file. The
typeperf utility allows you to periodically print on the console the value of certain performance metrics.
DiskPart utility is a text-mode command interpreter that allows you to manage disks, partitions, or volumes. Then there are
driverquery for looking at installed drivers and their configuration properties,
for managing printer jobs,
prncnfg for managing printers and their configurations, and
prnqctl for starting, stopping and pausing printers. The
sc utility comes with a huge number of options that together
provide a complete solution for managing services on a server from the command line. You can do anything from installing and starting a service to changing its textual description. Finally, the
will appeal to the Unix fans in that they allow you to look at the list of running proceses and kill unwanted ones all from the command line.
In this article, we tried to cover some of the more interesting features of this new line of server operating systems from Microsoft. Comparing this transition to that from Windows NT to Windows 2000, it seems like more of an incremental release than a major new release, despite what you might guess by the complete change in the naming scheme. The focus of this new release is on improving the reliability, performance, and security of the server. The enhancements to the boot process are clearly noticeable, and the new release of IIS offers lots of new features that are intended to bring out the best of the built-in .NET Framework that you've been hearing so much about.
Odysseas Pentakalos has been an independent consultant for 10 years in performance modeling and tuning of computer systems and in object-oriented design and development.
O'Reilly & Associates recently released (December 2001) Windows 2000 Performance Guide.
Sample Chapter 5 Multiprocessing, is available free online.
For more information, or to order the book, click here.