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<HTML> <HEAD> <TITLE> FastCGI </TITLE> <META NAME="GENERATOR" CONTENT="Internet Assistant for Microsoft Word 2.0z"><STYLE TYPE="text/css"> div.c5 {font-family: Arial Narrow; font-size: 80%; text-align: center} span.c4 {font-family: Courier} tt.c3 {font-family: Courier} div.c2 {text-align: center} div.c1 {color: #FFFFFF; font-family: Impact; font-size: 120%; text-align: center}</STYLE> </HEAD> <!--Copyright (c) 1996 Open Market, Inc. --> <!--See the file "LICENSE.TERMS" for information on usage and redistribution--> <!--of this file, and for a DISCLAIMER OF ALL WARRANTIES. --> <!-- $Id: fastcgi.htm,v 1.4 2002/02/25 00:45:06 robs Exp $ --> <BODY> <P> Open Market, Inc. </P> <P> </P> <DIV CLASS="c1"> Technical White Paper<BR> </DIV> <H1> FastCGI:<BR> A High-Performance Web Server Interface </H1> <P> April 1996<!--Please send comments to:--> </P> <HR> <!-- payne@openmarket.com--> <H2> 1. Introduction </H2> <P> The surge in the use of the Web by business has created a tremendous need for server extension applications that create dynamic content. These are the applications that will allow businesses to deliver products, services, and messages whose shape and content are in part determined by the interaction with, and knowledge of, the customers to which they are delivered. </P> <P> This important movement away from static Web content is pushing the limits and exposing the weaknesses of the environment in which these applications are currently bound: CGI (Common Gateway Interface). Most importantly it does not offer the performance these applications require. A new communication infrastructure is needed to connect Web servers with these new applications. This is what led Open Market to develop FastCGI. </P> <P> FastCGI is a fast, open, and secure Web server interface that solves the performance problems inherent in CGI, without introducing the overhead and complexity of proprietary APIs (Application Programming Interfaces). </P> <P> This paper assumes that the reader has basic familiarity with Web technology and developing Web applications. </P> <H3> Common Gateway Interface </H3> <P> The de facto standard interface for Web server applications is CGI, which was first implemented in the NCSA server. CGI has many benefits: </P> <UL> <LI> <B>Simplicity.</B> <SPAN>It is easy to understand.</SPAN> </LI> <LI> <B>Language independence.</B> CGI applications can be written in nearly any language. </LI> <LI> <B>Process isolation.</B> Since applications run in separate processes, buggy applications cannot crash the Web server or access the server's private internal state. </LI> <LI> <B>Open standard.</B> Some form of CGI has been implemented on every Web server. </LI> <LI> <B>Architecture independence.</B> CGI is not tied to any particular server architecture (single threaded, multi-threaded, etc.). </LI> </UL> <P> CGI also has some significant drawbacks. The leading problem is performance: Since a new process is created for each request and thrown away when the request is done, efficiency is poor. </P> <P> CGI also has limited functionality: It only supports a simple "responder" role, where the application generates the response that is returned to the client. CGI programs can't link into other stages of Web server request processing, such as authorization and logging. </P> <H3> Server APIs </H3> <P> In response to the performance problems for CGI, several vendors have developed APIs for their servers. The two most notable are NSAPI from Netscape and ISAPI from Microsoft. The freely available Apache server also has an API. </P> <P> Applications linked into the server API may be significantly faster than CGI programs. The CGI startup/initialization problem is improved, because the application runs in the server process and is persistent across requests. Web server APIs also offer more functionality than CGI: you can write extensions that perform access control, get access to the server's log file, and link in to other stages in the server's request processing. </P> <P> However, APIs sacrifice all of CGI's benefits. Vendor APIs have the following problems: </P> <UL> <LI> <B>Complexity.</B> Vendor APIs introduce a steep learning curve, with increased implementation and maintenance costs. </LI> <LI> <B>Language dependence.</B> Applications have to be written in a language supported by the vendor API (usually C/C++). Perl, the most popular language for CGI programs, can't be used with any existing vendor API. </LI> <LI> <B>No process isolation.</B> <SPAN>Since the applications run in the server's address space, buggy applications can corrupt the core server (or each other). A malicious or buggy application can compromise server security, and bugs in the core server can corrupt applications.</SPAN> </LI> <LI> <B>Proprietary.</B> Coding your application to a particular API locks you into a particular vendor's server. </LI> <LI> <B>Tie-in to server architecture.</B> API applications have to share the same architecture as the server: If the Web server is multi-threaded, the application has to be thread-safe. If the Web server has single-threaded processes, multi-threaded applications don't gain any performance advantage. Also, when the vendor changes the server's architecture, the API will usually have to change, and applications will have to be adapted or rewritten. </LI> </UL> <H3> FastCGI </H3> <P> The FastCGI interface combines the best aspects of CGI and vendor APIs. Like CGI, FastCGI applications run in separate, isolated processes. FastCGI's advantages include: </P> <UL> <LI> <B>Performance.</B> FastCGI processes are persistent-they are reused to handle multiple requests. This solves the CGI performance problem of creating new processes for each request. </LI> <LI> <B>Simplicity, with easy migration from CGI.</B> The FastCGI application library (described on page 9) simplifies the migration of existing CGI applications. Applications built with the application library can also run as CGI programs, for backward compatibility with old Web servers. </LI> <LI> <B>Language independence.</B> Like CGI, FastCGI applications can be written in any language, not just languages supported by the vendor API. </LI> <LI> <B>Process isolation.</B> A buggy FastCGI application cannot crash or corrupt the core server or other applications. A malicious FastCGI application cannot steal any secrets (such as session keys for encryption) from the Web server. </LI> <LI> <B>Non-proprietary.</B> FastCGI is supported in all of Open Market's server products, and support is under development for other Web servers, including the freely available Apache and NCSA servers, as well as commercial servers from Microsoft and Netscape. </LI> <LI> <B>Architecture independence.</B> The FastCGI interface is not tied to a particular server architecture. Any Web server can implement the FastCGI interface. Also, FastCGI does not impose any architecture on the application: applications can be single or multi-threaded, regardless of the threading architecture of the Web server. </LI> <LI> <B>Support for distributed computing.</B> FastCGI provides the ability to run applications remotely, which is useful for distributing load and managing external Web sites. </LI> </UL> <P> The following sections describe the FastCGI interface, protocol, application library, and support in Open Market's WebServer products. </P> <H2> 2. FastCGI Interface </H2> <P> The functionality provided by the FastCGI interface is very similar to that provided by CGI. To best understand the FastCGI protocol, we review the CGI interface here. Basic CGI request processing proceeds as follows: </P> <OL> <LI> For each request, the server creates a new process and the process initializes itself. </LI> <LI> The Web server passes the request information (such as remote host, username, HTTP headers, etc.) to the CGI program in environment variables. </LI> <LI> The Web server sends any client input (such as user-entered field values from an HTML form) to the CGI program's standard input. </LI> <LI> The CGI program writes any output to be returned to the client on standard output. Error information written to standard error is logged by the Web server. </LI> <LI> When the CGI process exits, the request is complete. </LI> </OL> <P> FastCGI is conceptually very similar to CGI, with two major differences: </P> <UL> <LI> FastCGI processes are persistent: after finishing a request, they wait for a new request instead of exiting. </LI> <LI> Instead of using operating system environment variables and pipes, the FastCGI protocol multiplexes the environment information, standard input, output and error over a single full-duplex connection. This allows FastCGI programs to run on remote machines, using TCP connections between the Web server and the FastCGI application. </LI> </UL> <P> Request processing in a single-threaded FastCGI application proceeds as follows: </P> <OL> <LI> The Web server creates FastCGI application processes to handle requests. The processes may be created at startup, or created on demand. </LI> <LI> The FastCGI program initializes itself, and waits for a new connection from the Web server. </LI> <LI> When a client request comes in, the Web server opens a connection to the FastCGI process. The server sends the CGI environment variable information and standard input over the connection. </LI> <LI> The FastCGI process sends the standard output and error information back to the server over the same connection. </LI> <LI> When the FastCGI process closes the connection, the request is complete. The FastCGI process then waits for another connection from the Web server. </LI> </OL> <P> FastCGI applications can run locally (on the same machine as the Web server) or remotely. For local applications, the server uses a full-duplex pipe to connect to the FastCGI application process. For remote applications, the server uses a TCP connection. </P> <P> FastCGI applications can be single-threaded or multi-threaded. For single threaded applications, the Web server maintains a pool of processes (if the application is running locally) to handle client requests. The size of the pool is user configurable. Multi-threaded FastCGI applications may accept multiple connections from the Web server and handle them simultaneously in a single process. (For example, Java's built-in multi-threading, garbage collection, synchronization primitives, and platform independence make it a natural implementation language for multi-threaded FastCGI applications.) </P> <H3> Remote FastCGI </H3> <P> FastCGI's ability to run applications remotely (over a TCP connection) provides some major benefits. These benefits are described in this section, along with some of the security issues that affect remote FastCGI applications. </P> <H4> FastCGI with Firewalls </H4> <P> Applications that run on organizational (external) Web servers and depend on internal databases can be a challenge to administer. Figure 1 shows a typical organization, with an external Web server, a firewall⌨️ 快捷键说明
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