Patent Publication Number: US-7594230-B2

Title: Web server architecture

Description:
RELATED PATENT APPLICATIONS 
   This U.S. Patent Application is a Continuation-in-Part (CIP) application and claims the benefit of priority of U.S. patent application Ser. No. 09/878,950, filed Jun. 11, 2001, now issued as U.S. Pat. No. 7,430,738. 
   This U.S. patent application further claims the benefit of priority from, and hereby incorporates by reference the entire disclosure of, co-pending U.S. Provisional Application for Letters Patent Ser. No. 60/367,013, filed Mar. 22, 2002, and titled “Web Server Architecture Split Into Processes Based on Functionality”. 
   This U.S. Patent Application is related to U.S. application patent Ser. No. 10/377,148, filed Feb. 28, 2003, and titled “Ensuring the Health and Availability of Web Applications”, now U.S. Pat. No. 7,225,362. 
   This U.S. Patent Application is related to U.S. application patent Ser. No. 10/377,176, filed Feb. 28, 2003, and titled “Web Garden Application Pools Having a Plurality of User-Mode Web Applications”, now U.S. Pat. No. 7,228,551. 

   TECHNICAL FIELD 
   The present invention relates generally to computers and like devices, and more particularly to methods, apparatuses and systems for an improved web server architecture. 
   BACKGROUND 
   The popularity of the Internet, and in particular, the portion of the Internet known as the World Wide Web, continues to grow. The World Wide Web is basically a collection of computers that are operatively linked together through a plurality of communication networks. Typically, users access the World Wide Web through a personal computer or like device, which is connected to the Internet via a modem of some type. For example, many users of the World Wide Web connect to the Internet using a dial-up telephone networked modem configured to establish data communications through an Internet Services Provider (ISP). Other users connect to the Internet with a faster modem, e.g., a cable modem, digital subscriber line (DSL) modem, etc. 
   Regardless of how a user ultimately connects to the Internet/World Wide Web, once connected the user typically accesses information available therein by using a web browser or like application. A web browser is configured to access web pages that are provided through the Internet by other computers. For example, one or more web server computers may be connected to the Internet and configured with one or more web sites or other supporting web applications. A web site typically has one or more static web pages and/or is capable of supplying one or more dynamically generated web pages that the user may selectively download, view and possible interact with. 
   To identify a particular web site/page the user will typically select a hyper link to the desired web site/page or may choose to manually enter a unique name for the web site/page. The most common name used for identifying a web site/page is known as the uniform resource locator (URL). By entering a URL, the user will be connected to an appropriate web server which hosts the applicable web application(s), and the requested web page will be downloaded, in this case using a hypertext transfer protocol (HTTP), to the web browser. Within the Internet itself, the selected URL is associated with a specific Internet Protocol (IP) address. This IP address takes the form of a unique numerical identifier, which has been assigned to the targeted web server. Thus, a user may also directly enter an IP address in the web browser. However, the majority of users tend to favor the use of the more easily remembered and entered URL. 
   When a typical web server receives a request, e.g., an HTTP request, from a web browser, it needs to handle the request. Hence, a web server process may be configured to handle the request itself, or may need to pass the request on to another process, e.g., a worker process, that is configured to handle the request. Conventional web server processes tend to listen to a particular port (e.g., “port 80”) provided by a Transmission Control Protocol/Internet Protocol (TCP/IP) kernel-mode provided service. When a request is received, the web server process either handles the request or calls for a worker process to handle the request. To determine which worker process should handle the request, most conventional web server processes either map the request to a physical file or to a dynamic application of some sort, such as a DLL or CGI process. Mapping is typically based on the extension provided at the end of the URL. For example, an “.html” extension signifies that the desired web page is in a HyperText Markup Language format. This extension could then be found, for example, in a look-up table, and associated with a specific worker process, if needed. Conversely, the .html extension may identify that the web server process can handle the request itself. There exists a plurality of extensions that may be used to identify the applicable worker process. 
   Once a specific worker process has been identified, the worker process is started (as needed) and the request is forwarded to the worker process. Such decisions and subsequent routing of the request are conducted by user-mode processes. Note that the web server process is a user-mode process too. 
   Unfortunately, there is usually a delay associated with such user-mode, “process hops”. For web servers, which often receive thousands of requests each minute, the delays associated with process hops can diminish the efficiency of the web server. In certain configurations, the web server process may be required to share a common communication port with one or more worker processes. This too may further reduce the efficiency of the web server. Moreover, there can be a reduction in the robustness of the web server in certain situations, e.g., when a worker process fails to receive/complete the request, etc. 
   To further illustrate such problems, reference is made to  FIG. 2 , which depicts an exemplary conventional web server arrangement  200 . Here, requests are received from a client computer, e.g., over a network and applicable interfaces (not shown), by a kernel-mode TCP/IP service  202 . TCP/IP service  202  provides the request to a user-mode web server process  204  through a port. By way of example, web server process  204  may be an earlier generation IIS web server process as developed by Microsoft Corp. 
   As illustrated, web server process  204 , when needed, can initiate a process hop to one or more user-mode worker processes  206 , as represented by line  208 . Worker processes  208  may take the form of any of a variety of functions, and/or applications, which are configured to handle or otherwise support certain types of requests. To determine which of worker process  206  needs to handle a given request, web server process  204  can access a mapping function  210  (e.g., a table, list, etc.) and identify an appropriate worker process based on the extension-identifying portion of the URL in the request. Alternatively, web server  204  may require the assistance of a DLL  212  in making such a decision. Here, for example DLL  212  or a like capability would identify the appropriate worker process based on the extension-identifying portion of the URL in the request. 
     FIG. 3  presents a flow chart depicting an exemplary conventional method  300  for handling requests received by web server arrangement  200 . In step  302 , the request is received by TCP/IP service  202  and passed on to web server process  204 . Next, in step  304 , web server  204  determines if there is a need to invoke a worker process  206 . Again this is typically determined based on the extension-identifying portion of the URL. The extension-identifying portion of the URL essentially identifies the type of data associated with the defined, and consequently may be used to redirect or route the request to an applicable user-mode process. The next step,  306 , is to pass or route the request to the applicable user-mode process for further handling. 
   As shown, in certain configurations, step  304  can be replaced or otherwise supported/enhanced by step  308 , which in this example routes the request to DLL  212  or other like user-mode process to help determine which user-mode worker process  206  would be appropriate to handle the request. As in step  304 , step  308  would also likely use the extension-identifying portion of the URL to help make such decisions. 
   As mentioned earlier, there are several drawbacks to web server arrangement  200  and associated method  300 . One of the major drawbacks is the inherent delay associated with each user-mode process hop (e.g., cross-process context switch). Another is the need to multiplex or otherwise share the use of one or more communication ports between user-mode processes. Yet another is often the lack of management over the worker processes, especially, for example, should one fail during the processing of a request. 
   As such, there is need for improved methods, apparatuses and systems that provide an improved web server environment/design. 
   SUMMARY 
   The above stated needs and others are met, for example, by a system in accordance with certain implementations of the present invention. The system in includes a user-mode web administrative service (WAS) and a kernel-mode HTTP listener (HTTP.sys) that is operatively coupled to the WAS and can be configured by the WAS to receive web requests and selectively store at least one web request in a request queue. The system further includes at least one user-mode worker process (WP) that is operatively coupled to the WAS and the HTTP.sys and configured to process the web request stored in the request queue. 
   In certain further implementations, the WAS has a configuration manager that is configured to identify at least one application pool to which the WP belongs. The application pool is associated with the request queue. A metabase coupled to the WAS allows the configuration manager to access configuration information needed to establish a corresponding configuration file that is used by the HTTP.sys. 
   The WAS may also include a process manager that is configured to control the various WPs that may be required to handle the queued web requests. Here, for example, the process manager may selectively start a WP and selectively stop the WP. The HTTP.sys will identify if certain WPs are in demand. 
   In certain further implementations, the HTTP.sys is configured to forward web request responses generated by the WPs to the original requesting client. The HTTP.sys may also be configured to cache selected web request responses and automatically forward them to subsequently requesting client. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A more complete understanding of the various methods, apparatuses and systems of the present invention may be had by reference to the following detailed description when taken in conjunction with the accompanying drawings wherein: 
       FIG. 1  is a block diagram that depicts an exemplary device, in the form of a computer, which is suitable for use with certain implementations of the present invention. 
       FIG. 2  is a block diagram depicting certain kernel-mode and user-mode processes associated with a conventional web server. 
       FIG. 3  is a flow chart depicting a conventional method for handling requests using the web server in  FIG. 2 . 
       FIG. 4  is a block diagram depicting certain kernel-mode and user-mode processes, including a kernel-mode universal listener (HTTP.sys) process, associated with an improved web server in accordance with certain exemplary implementations of the present invention. 
       FIG. 5  is a flow chart depicting a method for handling requests using an improved web server, for example, as in  FIG. 4 , in accordance with certain exemplary implementations of the present invention. 
       FIG. 6  is a block diagram depicting an improved web server arrangement that builds upon the web server arrangement in  FIG. 4 , in accordance with certain further implementations of the present invention. 
   

   DESCRIPTION 
   Overview 
   This description is divided into five sections, each of which builds upon one or more of the previous section(s). 
   The first section presents an exemplary computing environment. 
   The second section presents exemplary techniques for improving request handling in a web server. Here, for example, an improved web server design is introduced to handle requests, based on URLs or the like, within a kernel-mode universal listener process. Such techniques are the subject of the parent U.S. patent application Ser. No. 09/878,950, filed on Jun. 11, 2001, which is incorporated in its entirety herein by reference, now issued as U.S. Pat. No. 7,430,738. 
   The third section presents certain further exemplary techniques for use in the improved web server architecture. Here, for example, the kernel-mode universal listener process includes a request queuing capability and caching capabilities. The user-mode Web Administrative Service introduced in the first section is further configured with a process manager capability in addition to its configuration capability. 
   The fourth section describes exemplary techniques, further in accordance with certain aspects of the present invention, for ensuring the health/availability of web applications within such improved web server architectures and/or other like arrangements. Such techniques are the subject of U.S. patent application Ser. No. 10/377,148, filed Feb. 28, 2003, and titled “Ensuring the Health and Availability of Web Applications”, now U.S. Pat. No. 7,225,362, which is incorporated in its entirety herein by reference. 
   The fifth section describes exemplary techniques for creating and managing web gardens that include a plurality of instances of a user-mode web application. Such techniques are the subject of U.S. application patent Ser. No. 10/377,176, filed Feb. 28, 2003, and titled “Web Garden Application Pools Having a Plurality of User-Mode Web Applications”, now U.S. Pat. No. 7,228,551. 
   Exemplary Computing Environment 
   Turning to the drawings, wherein like reference numerals refer to like elements, the invention is illustrated as being implemented in a suitable computing environment. Although not required, the invention will be described in the general context of computer-executable instructions, such as program modules, being executed by a server computer, which may take the form of a personal computer, a workstation, a dedicated server, a plurality of processors, a mainframe computer, etc. Generally, program modules include routines, programs, objects, components, data structures, etc. that perform particular tasks or implement particular abstract data types. The invention may also be practiced in distributed computing environments where tasks are performed by remote processing devices that are linked through a communications network. In a distributed computing environment, program modules may be located in both local and remote memory storage devices. 
     FIG. 1  illustrates an example of a suitable computing environment  120  on which the subsequently described methods and arrangements may be implemented. 
   Exemplary computing environment  120  is only one example of a suitable computing environment and is not intended to suggest any limitation as to the scope of use or functionality of the improved methods and arrangements described herein. Neither should computing environment  120  be interpreted as having any dependency or requirement relating to any one or combination of components illustrated in computing environment  120 . 
   The improved methods and arrangements herein are operational with numerous other general purpose or special purpose computing system environments or configurations. 
   As shown in  FIG. 1 , computing environment  120  includes a general-purpose computing device in the form of a computer  130 . The components of computer  130  may include one or more processors or processing units  132 , a system memory  134 , and a bus  136  that couples various system components including system memory  134  to processor  132 . 
   Bus  136  represents one or more of any of several types of bus structures, including a memory bus or memory controller, a peripheral bus, an accelerated graphics port, and a processor or local bus using any of a variety of bus architectures. By way of example, and not limitation, such architectures include Industry Standard Architecture (ISA) bus, Micro Channel Architecture (MCA) bus, Enhanced ISA (EISA) bus, Video Electronics Standards Association (VESA) local bus, and Peripheral Component Interconnects (PCI) bus also known as Mezzanine bus. 
   Computer  130  typically includes a variety of computer readable media. Such media may be any available media that is accessible by computer  130 , and it includes both volatile and non-volatile media, removable and non-removable media. 
   In  FIG. 1 , system memory  134  includes computer readable media in the form of volatile memory, such as random access memory (RAM)  140 , and/or non-volatile memory, such as read only memory (ROM)  138 . A basic input/output system (BIOS)  142 , containing the basic routines that help to transfer information between elements within computer  130 , such as during start-up, is stored in ROM  138 . RAM  140  typically contains data and/or program modules that are immediately accessible to and/or presently being operated on by processor  132 . 
   Computer  130  may further include other removable/non-removable, volatile/non-volatile computer storage media. For example,  FIG. 1  illustrates a hard disk drive  144  for reading from and writing to a non-removable, non-volatile magnetic media (not shown and typically called a “hard drive”), a magnetic disk drive  146  for reading from and writing to a removable, non-volatile magnetic disk  148  (e.g., a “floppy disk”), and an optical disk drive  150  for reading from or writing to a removable, non-volatile optical disk  152  such as a CD-ROM, CD-R, CD-RW, DVD-ROM, DVD-RAM or other optical media. Hard disk drive  144 , magnetic disk drive  146  and optical disk drive  150  are each connected to bus  136  by one or more interfaces  154 . 
   The drives and associated computer-readable media provide nonvolatile storage of computer readable instructions, data structures, program modules, and other data for computer  130 . Although the exemplary environment described herein employs a hard disk, a removable magnetic disk  148  and a removable optical disk  152 , it should be appreciated by those skilled in the art that other types of computer readable media which can store data that is accessible by a computer, such as magnetic cassettes, flash memory cards, digital video disks, random access memories (RAMs), read only memories (ROM), and the like, may also be used in the exemplary operating environment. 
   A number of program modules may be stored on the hard disk, magnetic disk  148 , optical disk  152 , ROM  138 , or RAM  140 , including, e.g., an operating system  158 , one or more application programs  160 , other program modules  162 , and program data  164 . 
   The improved methods and arrangements described herein may be implemented within operating system  158 , one or more application programs  160 , other program modules  162 , and/or program data  164 . 
   A user may provide commands and information into computer  130  through input devices such as keyboard  166  and pointing device  168  (such as a “mouse”). Other input devices (not shown) may include a microphone, joystick, game pad, satellite dish, serial port, scanner, camera, etc. These and other input devices are connected to the processing unit  132  through a user input interface  170  that is coupled to bus  136 , but may be connected by other interface and bus structures, such as a parallel port, game port, or a universal serial bus (USB). 
   A monitor  172  or other type of display device is also connected to bus  136  via an interface, such as a video adapter  174 . In addition to monitor  172 , personal computers typically include other peripheral output devices (not shown), such as speakers and printers, which may be connected through output peripheral interface  175 . 
   Computer  130  may operate in a networked environment using logical connections to one or more remote computers, such as a remote computer  182 . Remote computer  182  may include many or all of the elements and features described herein relative to computer  130 . 
   Logical connections shown in  FIG. 1  are a local area network (LAN)  177  and a general wide area network (WAN)  179 . Such networking environments are commonplace in offices, enterprise-wide computer networks, intranets, and the Internet. 
   When used in a LAN networking environment, computer  130  is connected to LAN  177  via network interface or adapter  186 . When used in a WAN networking environment, the computer typically includes a modem  178  or other means for establishing communications over WAN  179 . Modem  178 , which may be internal or external, may be connected to system bus  136  via the user input interface  170  or other appropriate mechanism. 
   Depicted in  FIG. 1 , is a specific implementation of a WAN via the Internet. Here, computer  130  employs modem  178  to establish communications with at least one remote computer  182  via the Internet  180 . 
   In a networked environment, program modules depicted relative to computer  130 , or portions thereof, may be stored in a remote memory storage device. Thus, e.g., as depicted in  FIG. 1 , remote application programs  189  may reside on a memory device of remote computer  182 . It will be appreciated that the network connections shown and described are exemplary and other means of establishing a communications link between the computers may be used. 
   Improved Request Handling Techniques 
   Attention is drawn to the exemplary improved web server arrangement  400  that is depicted in  FIG. 4 . Here, as shown and described below, certain functions have been determined and designed to be handled by either kernel-mode processes or user-mode processes. In the past, web servers tended to be strictly user-mode processes. 
   With this in mind, improved web server arrangement  400  includes a kernel-mode universal listener (HTTP.sys) service  402 , which is provided on top of TCP/IP service  202 . HTTP.sys service  402  includes or otherwise is configured to access a configuration file  404 . For purposes of simplicity, in this example configuration file  404  is illustrated as being logically within the representative block of HTTP.sys service  402 . 
   Configuration file  404  is configured to support a decision process that determines which, if any, user-mode process should handle a request as received via TCP/IP service  202 . Rather than examining the extension-identifying portion of the URL in the received request to make such a determination, HTTP.sys service  402  and configuration file  404  are configured to examine the hierarchical formatted information in the URL. The resulting decision will then cause HTTP.sys service  402  to either deny the request or provide the request to a most-appropriate user-mode process. In certain implementations, HTTP.sys service  402  stores the configuration information as a tree of URL&#39;s in memory, rather than as a file. 
   For example, as shown, worker process  410  may pull or otherwise retrieve/receive the request from HTTP.sys service  402  for further handling. Doing so essentially eliminates user-mode process hops and associated processing delays because the request goes straight to the appropriate user-mode process instead of going through an intermediate user-mode process. Further, each of the user-mode processes can be supported by a private (non-shared) interface with kernel-mode HTTP.sys service  402 . Additionally, HTTP.sys service  402  may be advantageously configured to provide improved management over such interfaces and/or the various user-mode processes. 
   In accordance with certain implementations, configuration file  404  is updated or otherwise managed via a user-mode Web Administration Service (WAS) process  412 . As depicted, WAS process  412  is operatively associated with a configuration store  414 . Configuration store  414  provides the necessary information about the structure/configuration of web server arrangement  400  to allow for certain associations to be made between at least a portion of the available web accessible sites/pages/services provided therein and the supporting user-mode processes. For example, configuration store  414  may define a plurality of application pools  416 , each having associated with it one or more user-mode process identifiers  418 . 
   WAS process  412  maintains configuration file  404  using the associated information in configuration store  414 . Thus, for example, configuration file  404  may include a listing or similar tree-like arrangement that can be quickly examined upon receiving a request based on the hierarchical portion of the URL. A plurality of data may be associated together in configuration groups such that HTTP.sys service  402  can begin to systematically “walk through” the hierarchical portion of the requested URL to find the best matching configuration group and once found identify the most-appropriate application pool. 
   Those skilled in the art will recognize that configuration store  414 , and configuration file  404 , and/or sub-portions thereof may be arranged/configured using a variety of different data handling/processing techniques. A tree-like structure is therefore just one exemplary type data association technique. Preferably, the selected technique will support quick searching in order to find the best matching configuration group, etc., based on the requested URL. 
   Configuration file  404  may also provide guidance or define logical rules with regard to the selection of a user-mode process in a given application pool  416 . Thus, for example, a possible rule may prioritize the use of user-mode processes according to some scheme. One such exemplary scheme may cause HTTP.sys service  402  to look for already running user-mode processes, rather than start a new user-mode process. Rules may also be provided to better manage the private interfaces and the running/halting/closing of user-mode processes. 
   WAS process  412  is configured to provide user administration capabilities in configuring, maintaining, or otherwise modifying all or part of configuration store  414 . Thus, for example, a web server administrator may add/delete data, or otherwise modify existing data in configuration store  414 , as needed. In certain configurations, the administrator may be able to define one or more rules or parameters that operatively affect the operation of HTTP.sys service  402 . In other exemplary implementations, one or more automated or semi-automated user-mode processes/applications may be used to gather and/or otherwise provide data for use in configuration store  414 . 
   Reference is now made to  FIG. 5 , which is a flow chart depicting an improved process  500  for use in handling requests in a web server arrangement. In act  502 , WAS process  412  updates or otherwise establishes/maintains the configuration group(s) in configuration file  404  associated with kernel-mode HTTP.sys service  402 , based on information in configuration store  414 . Next, in act  504 , a request is received from a client device by HTTP.sys process  402 , e.g., via TCP/IP service  202  and interconnecting network services/arrangements. The request includes a URL. 
   In act  506 , HTTP.sys service  402  examines the URL in the received request and searches or in some other manner attempts to identify a most appropriate user-mode application pool  416  associated with a best matching configuration group. For example, the best matching configuration group might be the configuration group defined in configuration file  404  that best matches the URL. 
   Next, in act  508 , the most appropriate user-mode process identified in the application pool is started (if needed) and/or otherwise communicated with by HTTP.sys service  402  and provided with the request for further handling. In certain instances, there may be a need to have the request handled by more than one user-mode process. 
   Further Improved Web Server Architecture 
   Some of the goals satisfied in creating the improved web server architecture included providing a web server arrangement that was more reliable, stable, secure, and performed better than conventional web server arrangements. Web server arrangement  400  (described in the section above) sought to separate certain functions and handle some of them in kernel-mode processes and others in user-mode processes. These techniques and ideas are expanded upon in this section, in accordance with certain exemplary implementations of the present invention. 
   Attention is drawn to  FIG. 6 . Here, a web server arrangement  400 ′ continues to be divided into key portions based on functionality. Request reception and routing are handled by a HTTP.sys service  402 ′ in the kernel, a WAS process  412 ′ is provided as a separate user-mode process that may fail (crash) without necessarily affecting kernel-mode HTTP.sys service  402 ′. In this example, WAS process  412 ′ includes a configuration manager  604  and a process manager  606 . The actual web application processing is done within separate users mode processes (e.g., worker processes  410   a ,  410   b  and  410   n , and in-process applications  608   a ,  608   b  and  608   n ) that may also crash without affecting kernel-mode HTTP.sys service  402 ′, WAS process  412 ′, or other user-mode web application processes. In this way, software failures should be effectively isolated to only the host process, thereby allowing the web server to continue operating as if nothing happened. 
   Also depicted in  FIG. 6  is a metabase  600  that can be accessed by web server  602 , and more particularly by WAS process  412 ′ therein. Metabase  600  may include, for example, configuration store  414 , as previously described. HTTP.sys service  402 ′ includes a configuration file  404  and also includes a response cache  610  and request queues  612   a ,  612   b  and  612   n . Several application pools  608   a ,  608   b  and  608   n  are shown in the user-mode side of the architecture, as are worker processes  410   a ,  410   b  and  410   n.    
   In this exemplary implementation, HTTP.sys service  402 ′ is configured to receive and manage connection requests, parse incoming requests as they are received, and manage the size and routing of requests to the request queues. HTTP.sys service  402 ′ may also be configured to provide or otherwise support logging, such as, for example, text-based request hit logging. 
   Configuration manager  604  is responsible for configuring HTTP.sys service  402 ′ based on metabase  600 , and for periodically/continually updating HTTP.sys service  402 ′ with changes in web server configuration. Process manager  606  is responsible for managing the starting, stopping, and monitoring of the multiple web application processes, which serve the various application pools  608 . 
   The web application processes or worker processes  410  are the user-mode processes which are responsible for taking requests from the appropriate request queue  612 , loading and executing web application code (if applicable to the web request), and generating the response to be sent back to the client. Each worker process  410  serves just one application pool  608 . Thus, for example, as depicted worker process  410   a  serves application pool  608   a  and worker process  410   b  serves application pool  608   b . There can be multiple worker processes running at any given time. Application pool  608   n  illustrates that a plurality of worker processes  410   n  may be provided within one application pool. Application pools  608  are, as is previously described, basically named identifiers that are used to identify specific worker processes or “pools” of worker processes to which requests are routed. They also correspond to request queues within the HTTP.sys ( 612   a ,  612   b ,  612   n ). When web server  602  is started, WAS process  412 ′ will begin by reading the specific web site and application configuration from a configuration store in metabase  600  and proceed to configure HTTP.sys service  402 ′. Thus, for example, WAS process  412 ′ is configured to create a request queue  612  for each application pool  608 , configure HTTP.sys service  402 ′ as to which sites to listen to (e.g., sockets to open), and configure HTTP.sys service  402 ′ as to which request queue  612  to route various requests to. WAS process  412 ′ may also configure bandwidth and connection limits within HTTP.sys service  402 ′. 
   HTTP.sys service  402 ′ then opens communication sockets as configured by WAS process  412 ′ and begins listening for TCP/IP connection requests. Beyond accepting incoming requests, routing them to the appropriate user-mode worker process  410 , and sending the responses back to the clients, the Kernel-mode HTTP.sys service  402 ′ typically does no other request processing. Hence, HTTP.sys service  402 ′ receives requests, routes the requests, and forwards responses to the client (e.g., through TCP/IP  202  and/or the like). HTTP.sys service  402 ′ is not, however, responsible for loading and executing application code to generate the response. 
   One slight exception is that for certain requests, cache  610  in HTTP.sys service  402 ′ may include a previously generated and stored response that has been flagged or otherwise identified as being the correct response for any subsequent identical requests, or error conditions that HTTP.sys handles (such as connection limits). Thus, for example, worker process  410   b  may handle an initial request by generating a response, which is provided to HTTP.sys service  402 ′ for forwarding to the requesting client. Worker process  410   b  may also identify to HTTP.sys service  402 ′ that if such a request from this and/or from other clients is received, then the same response should be forwarded to the requesting clients. Thus, HTTP.sys service  402 ′ stores the response in cache  610 . In certain implementations, such cache-based responses may be limited to a specific period of time, a certain number of requests, and/or the continued health and availability of the worker process that initially generated the response. In some implementations, the worker process that initially generated the response may inform HTTP.sys service  402 ′ to clear certain cached responses. 
   Beyond managing the configuration of HTTP.sys service  402 ′, WAS process  412 ′ and more particularly process manager  606  is also responsible for managing the lifetime of the various worker processes  410 . For example, process manager  606  is responsible for starting up new worker processes, shutting down old/problematic processes, and ensuring that these processes are able to continue to accept requests from HTTP.sys service  402 ′. 
   Worker processes  410  are typically where third-party customer code is run and general web application processing is accomplished. When a worker process  410  is started by WAS process  412 ′ (process manager  606 ), it is informed as to which application pool  608  it serves. In accordance with certain exemplary implementations, a worker process  410  is configured to use an application pool ID when it communicates with HTTP.sys service  402 ′ to obtain new requests from within the kernel (e.g., from a request queue  612 ). 
   After obtaining a request from a request queue  612 , the worker process  410  will proceed to process that request, loading and executing whatever code (save CGI&#39;s or the like, which are executed out of process) is necessary and configured for that web application request. For example, worker process  410   a  may use in-process application  608   a . Worker process  410   a  eventually generates the response for the request and sends that response to HTTP.sys service  402 ′ for forwarding to the requesting client. 
   If the web application code or something else causes a worker process  410  to fail, for whatever reason, the termination of the worker process will not affect other worker processes that are servicing different request queues  612 . Likewise, clients generating requests for the failed worker process&#39; application pool will not be rejected simply because of the failure. HTTP.sys service  402 ′ and WAS process  412 ′ are not affected by this failure, because WAS process  412 ′ is running in separate process and HTTP.sys is part of the operating system kernel. HTTP.sys service  402 ′ will continue to accept requests and route them accordingly while process manager  606  starts a new worker process  410  to replace the failed worker process. 
   This arrangement also allows for increased performance while also providing increased reliability through process isolation. Each worker process will only serve the URL&#39;s that are routed to its application pool&#39;s request queue and will contact the kernel mode HTTP.sys service  402 ′ to get requests directly instead of having them routed through another user-mode processes. 
   As described in greater detail in the next section of this description, this architecture also enables health monitoring. As mentioned before, WAS process  412 ′ is also responsible for managing the individual web application worker processes. As part of this management role, process manager  606  can be configured to maintain some form of communication with each worker process  410 . This allows process manager  606  to periodically determine the health/availability of each worker process. 
   Techniques for Ensuring the Health/Availability of Web Applications 
   In accordance with certain further exemplary implementations, a series of related features are presented that are designed to allow improved web server arrangement  400 ′ to proactively and/or reactively recover from availability problems caused, for example, by worker process failures. 
   These features can be are divided into different categories. One category includes techniques that are essentially proactive ways to ensure the health of worker processes. By way of example, in some cases the health of a worker process  410  may be better ensured by periodically recycling it. 
   In accordance with certain implementations, if an Internet Server Application Programming Interface (ISAPI) extension that is able to report itself as unhealthy (for whatever reason), does so then an applicable worker process may be recycled to better ensure its health. 
   In other examples, if a worker process is idle for a certain amount of time, then it may be shut down to possibly free up resources for other processes. The health of some worker processes may be best ensured by only starting up the worker process when there is demand for it, e.g., a request is received. This has the added benefit that any shared resources would be available to other worker processes, such as, more frequently requested web applications. 
   Another category of features includes techniques that are essentially reactive ways to better ensure the health/availability of worker processes. One exemplary technique is to periodically ping worker processes, for example, to determine if there is at least one thread available to accept new work (requests). A worker process can be restarted if the ping fails. Alternatively, a debugging or other like process may be initiated and run on a ping-dead worker process. 
   Another technique includes, detecting when a worker process crashes unexpectedly and automatically restarting a new version of the worker process, for example, if there is a continuing demand for it. Yet another exemplary technique includes protecting the server itself from a repeated series of worker process failures by stopping the web applications assigned to the host process. 
   All or part of these exemplary collective methods can be employed to allow improved web server arrangement  400 ′ to ensure web application availability in light of faulty third party code, for example, which would otherwise cause the web server (and web applications) to possibly become unavailable for some period of time. 
   Such techniques and others like them can be operatively configured within WAS process  412 ′, and more particularly within process manager  606 . Some exemplary techniques are described in more detail in the following paragraphs. 
   Periodic Worker Process Recycling 
   By way of further example, process manager  606  can be configured to periodically refresh worker processes. The determination as to when to recycle or refresh a worker process  410  can be based on a variety of factors. For example, such factors may include the amount of time (e.g., number of minutes) that a worker process has been running, a scheduled time of day, the number of requests processed by the worker process, an amount of (private and/or virtual) memory associated with the worker process, and/or a demand from some process, such as, e.g., an administrative API. 
   Recycling is basically a technique that includes causing the old worker process to shutdown and starting a new worker process in its place. Recycling can be performed in a few different ways. One way to perform a recycle is what is referred to herein as an overlapping recycle. Another way is referred to as a non-overlapping recycle. Basically, in an overlapping recycle, process manager  606  will first start a new worker process while the old worker process is still running. Once the new worker process is ready to start handling requests then the old worker process is shutdown. Conversely, a non-overlapping recycle basically starts the new worker process after shutting down the old worker process. 
   By way of further example, in an overlapping recycle process manager  606  determines when to recycle a worker process, e.g., based on one or more of the factors described above. In certain other implementations, a WP determines when to recycle itself and does so by requesting that process manager  606  recycle it. In such implementations, process manager  606  may be configured to recycle a WP based on configuration changes, application pool identity changes, on demand, etc. 
   Next, process manager  606  starts a, new worker process while the old worker process continues to handle requests. The new worker process initializes and informs process manager  606  that it is ready to handle requests. The new worker process also hooks up to HTTP.sys service  402  and begins handling requests for the request queue (application pool) it is assigned to. Process manager  606  instructs the old worker process to revoke any outstanding instructions to HTTP.sys service  402  seeking a new request to handle. Process manager  606 , however, allows the old worker process to complete a request that has already been provided to it by HTTP.sys service  402 ′, after that the old worker process is shutdown. 
   In an exemplary non-overlapping recycle, process manager  606  again determines when to recycle a worker process, e.g., based on one or more of the factors described above. In other implementations, as mentioned above, the WP may determine when it needs to be recycled. 
   Process manager  606  then instructs the old worker process to revoke any outstanding instructions to HTTP.sys service  402 ′ seeking a new request to handle, but allows the old worker process to complete a request that has already been provided to it by HTTP.sys service  402 ′, after that the old worker process is shutdown. Process manager  606  may then start a new worker process automatically. In some circumstances process manager  606  may decide to wait until certain resources are available before starting the new worker process, or to wait for HTTP.sys service  402 ′ to request that a new worker process be started to meet client request demand. 
   In certain implementations, it may also be desirable to recycle all of the worker processes in an application pool  608 . 
   It should be understood that process manager  606  and/or a worker process  410  may be configured to log or otherwise output various information regarding the recycle process, or any other process or problem. 
   ISAPI Extensions Being Able to Report Themselves as Unhealthy 
   Web server  602  may also be configured to allow ISAPI extensions to call into the host process and report themselves as unhealthy and provide a string reason as to why. This string is then used, for example, to publish an event to an event log (not shown) and/or notify the system administrator that the ISAPI extension reported itself as unhealthy for the reason provided in the string. If worker process pinging is enabled, then the worker process may request a recycle immediately after responding to the health detecting ping message. By way of example, this would allows application environments, such as ASP and ASP.NET, to request a host process recycle if it gets into a bad state for whatever reason. 
   Idle Timeout of Web Application Host Processes 
   HTTP.sys service  402 ′ may also be configured to automatically time out idle worker processes and shut them down. Doing so may prevent idle worker processes from consuming resources that active applications may need, such as memory. Here, for example, HTTP.sys service  402 ′ may have a programmable timer or other like mechanism that essentially keeps track of how long it has been since a worker process has processed a request, and if a programmable threshold has been reached, then HTTP.sys service  402 ′ will request that process manager  606  shutdown the applicable worker process. 
   Demand Start of Web Application Host Processes 
   HTTP.sys service  402 ′ and process manager  606  can be configured to only start worker applications if there is demand for them (i.e., at least one request from a client has been received). Here, for example, process manager  606  will inform HTTP.sys service  402 ′ that it may request startup of a worker process  410  for a given request queue  612  should there be a demand for it. Thus, when a request from a client arrives, HTTP.sys service  402 ′ will check to see if there are any worker processes currently serving the applicable request queue and if not, HTTP.sys service  402 ′ will request that process manager  606  startup a new worker process to service the request queue. 
   Periodic Pinging of Web Application Host Processes 
   As mentioned above, process manager  606  can be configured to selectively/periodically ping each worker process  410 . The goal of this ping is to determine if there is at least one thread available to do work on requests. In accordance with certain exemplary implementations, such pings take the form of a health detection message that is sent over a named pipe that connects the WAS process  412 ′ and worker process  410 . The worker process then has a configured time limit in which to respond to the health detection message. If the worker process fails to respond to the health detection message within the configured time limit, then process manager  606  determines that the worker process is unhealthy and therefore terminates the worker process and starts a new one in its place. This activity is typically logged. 
   In certain implementations, if the worker process is determined to be unhealthy for failing to respond to the health detection message then instead of automatically terminating the worker process a debugging or orphan action can be taken. This may include, for example, taking a process dump of the offending/blocked worker process before terminating it 
   Crash Detection 
   Web server  602  may determine when a worker application  410  crashes since WAS process  412 ′ creates each of the processes and monitors them via Pinging or just being signaled on a process handle. Here, for example, process manager  606  maintains a process handle for each of the worker processes it has started and will be signaled on that handle by the operating system kernel if the worker process exits. This capability allows process manager  606  to then start a new worker process in the place of the failed worker process, if there should be demand for it. 
   Automatic Disabling of a Request Queue on Repeated Failures 
   Otherwise known as Rapid Fail Protection, this capability allows WAS process  412 ′ to prevent repeated worker process  410  creation and abnormal termination costs by keeping track of the number of times a worker process serving a particular request queue  612  has been restarted due to abnormal conditions. Basically, it allows WAS process  412 ′ to not put the server into a thrashing state due to a process crashing and restarting. 
   Instead, for example, process manager  606  can be configured to track the number of times a process has terminated abnormally (including health detection message failures and/or detected crashes) over a given period of time. If a preprogrammed abnormal restart threshold value is exceeded, then process manager  606  will inform HTTP.sys service  402 ′ to stop accepting new requests for the request queue associated with the suspect worker process. This may also lead to an application pool  608  being essentially shutdown. The application pool may, for example, be marked by process manager  606  as disabled in metabase  600  and in HTTP.sys also. HTTP.sys will not queue requests for an application pool that has been shutdown. 
   This shutdown feature allows web server  602  to use resources for other applications pools/worker processes rather than a web application group that&#39;s functioning poorly. This also adds additional security to the web server in the event to a denial of service attack or other like unsavory client activity. 
   Creating and Maintaining Web Gardens 
   In this section the concept of a “web garden” is introduced for use in the above improved web server arrangements. Here, the basic idea to provide the ability for process manager  606  to open a plurality of instances of a worker process and techniques for use in HTTP.sys service  402 ′ in routing web requests to the plurality of request queues associated with plurality of instances of the worker process. 
   With this in mind, as shown in  FIG. 6 , HTTP.sys service  402 ′ further includes web garden logic  620 . Application pool  608   n  is an example of a web garden since it has a plurality of instances of worker process  410   n . Associated with the plurality of instances of worker process  410   n  are an equal number of request queues  612   n.    
   An exemplary technique for creating this type of web garden includes deciding how large the web garden will be. For example, a maximum number of instances of a worker process can be defined in metabase  600 . This maximum number limits the size of the web garden. The web garden may, however, have fewer instances of worker processes. Although not necessary, in some implementations a corresponding minimum number of instances of a worker process may also be defined in metabase  600 . The default minimum number in this example is one. 
   Within these bounds, the web garden will be allowed to grow and shrink depending on the demand (e.g., web requests received) for the worker process  410   n . Thus, in accordance with certain implementations of the present invention, when configuration manager  604  creates and/or otherwise updates configuration file  404  the web garden boundaries are set. Assuming that there is only an upper bound, i.e., a maximum number of instances, in certain implementations that parameter defines the number of worker process  410   n  starts that HTTP.sys service  402 ′ may demand of process manager  606 . 
   In some exemplary implementations, a ticket-like configuration may be implemented to define how many of these demand starts are available at a given time. Thus, for example, configuration manager  604  may initially grant an applicable number of demand start tickets for worker process  410   n  to HTTP.sys service  402 ′, and more particularly to web garden logic  620 . These demand start tickets may be submitted or otherwise provided to process manager  606 , as needed. Upon receipt of a demand start ticket, process manager  606  would then start a new instance of worker process  410   n . If, for some reason, an instance of worker process  410   n  was stopped or terminated, then process manager could provide a new demand start ticket to web garden logic  620 . When web garden logic  620  is out of demand start tickets, then it cannot request any more instances of worker process  410   n.    
   With this exemplary ticket scheme or other similar schemes, web garden logic  620  can be configured to act in a variety of ways. One exemplary way in which web garden logic  620  may be configured to act is to always use an available demand start ticket when a new web request is received, until such time as all of the demand start tickets have been used. This tends to maximize the number of instances of worker process  410   n , which may provide better performance from the standpoint of requesting clients. There is, however, an increased processing burden on the web server itself. 
   In certain implementations, when web garden logic  620  submits a demand start ticket to process manager  606  it will not make the web request wait for the new instance of worker process  410   n  to complete initialization so long as other instances are already running. In this situation, web garden logic  620  will place the web request in an appropriate existing request queue  612   n  and another instance will eventually handle the web request. 
   In certain further exemplary implementations, web garden logic  620  is configured to spread received TCP/IP connections among the available request queues. One technique that can be implemented is a round-robin distribution. In certain implementations, all web requests received over a connection are placed in the same request queue and eventually go to the same worker process. 
   Those skilled in the art will recognize that other distribution techniques may also be employed to meet certain requirements. Furthermore, such techniques may be optimized for use in computers having multiple processors, wherein selected processors are configured to handle certain worker processes  410   n.    
   Since an application pool can be a web garden, all of the previous techniques provided in this description may be applied to manage the worker processes  410   n.    
   In accordance with certain further implementations of the present invention, various techniques can be employed to selectively recycle the worker processes within a web garden. Rather than simply recycling all of the worker processes within a web garden at one time, in certain exemplary implementations a staggered recycling process is employed. For example, using staggered recycling one or more of the worker processes within a web garden are recycled while the other worker processes within the web garden remain active. 
   With this in mind, for example, certain staggered recycling techniques include determining when to recycle each worker process based on the maximum number of worker processes within a web garden and the number of requests received/handled. 
   Thus, for example, if a web garden is configured to have a maximum of four worker processes, then a recycle parameter can be set or otherwise determined to stagger the recycling of the worker processes such that each worker process recycles after a certain number of requests have been received and/or handled. Assuming that first, second, third, and fourth worker processes have been started in the web garden as a result of having received four requests, with the first worker process being the oldest and the fourth worker process being the newest, then a staggered recycling technique can be configured to cause the first worker process to recycle after fifth request is received. The second worker process would subsequently recycle after the tenth request is received, the third worker process after the fifteenth request is received, and the fourth worker process after the twentieth request is received. Thereafter, the oldest worker process would then be recycled after every twentieth request is received. 
   This is just one example as to how a staggered recycle may be implemented. Those skilled in the art will recognize that other staggered recycling techniques may be employed, for example, based on the number of received/handled requests, the number of worker processes, the maximum number of worker processes in the web garden, the age in time of the worker process, the health of a worker process, and/or other like factors that may help to identify when to recycle one or more worker processes. The staggered recycling technique may also be selectively applied, for example, based on time, based on demand, based on process health status, based on traffic loads, etc. However, implemented, one important concept of staggering the recycling of worker processes within a web garden is to hopefully recycle often enough to promote computationally-good running worker applications without significantly degrading the capability of the web garden and/or the server.