Concept understanding: cgi,fastcgi,php-cgi and PHP-FPM Common Gateway Interface Introduction

Cgi

The CGI name is a "public Gateway Interface" (Common Gateway Interface), a tool that the HTTP server "chats" with programs on your or other machines, and its programs must be run on a network server.

CGI can be written in any language, as long as the language has standard input, output, and environment variables. such as PHP,PERL,TCL and so on.

FastCGI

FastCGI is like a resident (long-live) CGI, which can be executed all the time, so long as it is activated, it will not take a moment to fork once (this is the most notorious fork-and-execute mode of CGI). It also supports distributed operations where the FastCGI program can execute and accept requests from other Web servers on hosts other than the Web server.

FastCGI is a language-independent, extensible architecture for CGI open extensions whose main behavior is to keep the CGI interpreter process in memory and thus achieve high performance. As we all know, the repeated loading of CGI interpreter is the main reason of poor CGI performance, if the CGI interpreter remains in memory and accepts the FASTCGI process manager scheduling, it can provide good performance, scalability, fail-over characteristics and so on.

FASTCGI Features

1. FastCGI is language agnostic.
2. FASTCGI applications in the process, run independently of the core Web server, provide a more secure environment than the API. APIs link the application's code with the core Web server, which means that an application in the wrong API can corrupt other applications or core servers. The application code of a malicious API can even steal a key from another application or core server.
3. FASTCGI technology currently supports languages such as C + +, Java, Perl, TCL, Python, SmallTalk, Ruby, and so on. Related modules are also available on popular servers such as Apache, ISS, lighttpd and more.
4. FastCGI does not depend on the internal architecture of any Web server, so fastcgi remains stable even if the server technology changes.

How the FastCGI works

1. Load fastcgi Process Manager (IIS ISAPI or Apache Module) when Web server starts
2. The FASTCGI process Manager itself initializes, starts multiple CGI interpreter processes (visible multiple php-cgi) and waits for a connection from the Web server.
3. When a client request arrives at the Web server, the FASTCGI process manager selects and connects to a CGI interpreter. WEB server sends CGI environment variables and standard input to the FASTCGI child process php-cgi.
4. The FASTCGI child process returns standard output and error information from the same connection to the Web Server after processing is complete. When the fastcgi child process closes the connection, the request is processed to completion. The fastcgi child process then waits and processes the next connection from the FASTCGI process Manager (running in Web server). In CGI mode, php-cgi exits here.

In the above scenario, you can imagine how slow CGI is usually. Every Web request PHP must re-parse php.ini, reload all extensions, and initialize all data structures. With fastcgi, all of this occurs only once when the process is started. An additional benefit is that the persistent database connection (persistent connection) can work.

FastCGI of the poor

Because it is multi-process, so consumes more server memory than CGI multithreading, php-cgi interpreter consumes 7 to 25 megabytes per process, multiplying this number by 50 or 100 is a large amount of memory.

Nginx 0.8.46+php 5.2.14 (FastCGI) server in 30,000 concurrent connection, open 10 Nginx process consumes 150M memory (15m*10=150m), open 64 php-cgi process consumes 1280M of memory (20m*64= 1280M), combined with the memory consumed by the system itself, consumes less than 2GB of memory. If the server memory is small, you can only open 25 php-cgi processes, so that the total amount of memory consumed by php-cgi is 500M.
The above data is from the Nginx 0.8.x + PHP 5.2.13 (FastCGI) build 10 times times more than Apache Web Server (6th edition)

php-cgi

PHP-CGI is the fastcgi manager that comes with PHP.

PHP-CGI deficiency:

1. php-cgi after changing the php.ini configuration, you need to restart the php-cgi for the new Php-ini to take effect, not to smooth the restart.
2. Directly kill the php-cgi process, PHP will not be able to run. (PHP-FPM and spawn-fcgi do not have this problem, the daemon will smooth the new child process from the newly generated.) ）

php-fpm

PHP-FPM is a PHP fastcgi manager that is only for PHP and can be downloaded in http://php-fpm.org/download.

PHP-FPM is actually a patch of PHP source code designed to integrate FASTCGI process management into a PHP package. It must be patch into your PHP source code and can be used after compiling and installing PHP.

Now we can download in the latest PHP 5.3.2 source tree to directly integrate the PHP-FPM branch, it is said that the next version will be fused into the main branch of PHP. Relative SPAWN-FCGI,PHP-FPM in the CPU and memory control are better, and the former is easy to crash, must be monitored with crontab, and PHP-FPM does not have this annoyance.

PHP5.3.3 has integrated php-fpm, no longer a third-party package. PHP-FPM provides a better way to manage the PHP process, can effectively control the memory and process, can be smooth overloaded PHP configuration, more than spawn-fcgi have a bit more, so by the official PHP included. The PHP-FPM can be turned on with the –ENABLE-FPM parameter when the./configure.

spawn-fcgi

SPAWN-FCGI is a general-purpose fastcgi Management Server, it is a part of LIGHTTPD, many people use lighttpd spawn-fcgi for fastcgi mode management work, but there are many shortcomings. And the php-fpm of how much to alleviate some of the problems, but PHP-FPM has a drawback is to recompile, which for some already running environment may have a small risk (refer), in PHP 5.3.3 can be directly used php-fpm.

SPAWN-FCGI has now become a single project, more stable, but also to many Web site configuration to facilitate. There are a number of sites to match it with Nginx to solve dynamic Web pages.

The newest lighttpd also does not contain this piece (Http://www.lighttpd.net/search?q=Spawn-FCGI), but it can be found in previous versions. Included in the lighttpd-1.4.15 version (http://www.lighttpd.net/download/lighttpd-1.4.15.tar.gz), the current spawn-fcgi is HTTP/// REDMINE.LIGHTTPD.NET/PROJECTS/SPAWN-FCGI, the latest version is http://www.lighttpd.net/download/spawn-fcgi-1.6.3.tar.gz.

Note: The latest spawn-fcgi can find the latest release address of the Lighttpd.net website by searching for "spawn-fcgi".

Comparison of PHP-FPM and spawn-cgi

The PHP-FPM is very convenient to use, the configuration is in the Php-fpm.ini file, and the start, restart can be done from the PHP/SBIN/PHP-FPM. More convenient is to modify the php.ini can be directly used php-fpm reload loading, without killing the process can be completed php.ini modified loading
The results show that using PHP-FPM can make PHP a little more performance-boosting. PHP-FPM controlled process CPU recovery is slow, memory allocation is very uniform.
SPAWN-FCGI-controlled processes CPU drops quickly, while memory allocations are not evenly spaced. There are many processes that do not seem to be allocated, while others occupy very high. This may be due to the uneven distribution of process tasks. This also leads to a decline in the overall response rate. The rational distribution of php-fpm leads to the reference of the overall response and the average of the task.

Concept understanding: cgi,fastcgi,php-cgi and PHP-FPM Common Gateway Interface Introduction