mod_perl High speed dynamic content

Definitions Apache – OpenSource httpd server Perl – OpenSource interpreted programming language mod_perl – OpenSource interface between Apache and Perl

Scenario Unix hosted web-site using CGI Perl scripts to create web pages with dynamic content. As the site becomes larger and more popular, the speed slows The web servers are not resource constrained How can we speed the delivery of content?

Topics covered Why use mod_perl? How mod_perl works Installation highlights Commonly encountered problems when porting from CGI to mod_perl

Take home messages use strict; Use the PerlTaintCheck directive mod_perl enabled scripts are fast Possibly faster than C code… Effective use of mod_perl is not trivial

Why use mod_perl? CGI scripts written in Perl and served from Apache can be slow Generally the more dynamic the content, the slower the page return As sites grow, their content usually becomes more dynamic Sites ported to mod_perl show request return rates 200% to 2000% higher!!!

Evolution of a web-site

Why is CGI slow? For each CGI script called: Apache must load the Perl interpreter Perl must load the the CGI script including all used Modules The CGI script must initialize itself on each load Database initialization is a common slow-down

Dynamic content options

The embedded interpreter There are increasingly sophisticated solutions: Only load the Perl interpreter once (PerlRun) Only load the CGI scripts and modules once (PerlRegistry) Only do initializations once (Code re-factoring)

The mod_perl version Each Apache instance loads the Perl interpreter when it initializes (PerlRun) mod_perl loads CGI scripts the first time they are executed (PerlRegistry) We can move CGI initialization code into a separate script that is executed when each Apache instance starts (Code re-factoring)

How does mod_perl work? Its invoked by Apache so… How does Apache work? Its running Perl code so… How does Perl work? The mod_perl handler

How does Perl work? Interpreted language To run a Perl program The Perl interpreter is loaded The Program is compiled by the Perl interpreter The Program is executed

array Analogous to the LD_LIBRARY_PATH environment variable This array contains the paths that Perl will search when loading libraries or modules With mod_perl this is set during Apaches initialization phase and cannot be change later

Perls %INC hash After Perl has compiled a program, it is added to %INC as a key with the fully qualified filename and compile time as a values Before loading a program, Perl searches %INC for a match. If it finds one, it uses the %INC entry and does not re-load the program

How does Apache work? Apache serves documents requested via HTTP A sample request:

The Apache request cycle

The mode _perl handlers You can interact with the Apache request cycle at any point with a handler A handler is a program that is defined for a Directory, Location, Files or FilesMatch directive in Apaches configuration files

The Apache handler API Apache calls the handler, passes information about the current transaction and server state and expects an integer status code in return If the handler returns an error, Apache short- circuits to the logging phase

The PerlHandler: part 1 Called prior to serving the requested document Two default handlers PerlRun PerlRegistry

The PerlHandler: part 2 Unless you are using a custom handler, your CGI programs are executed as subroutines inside the handler subroutine (nested subroutines) Since Apache never exits, the CGI programs are never reaped by Perls garbage collection

A handler subroutine sub handler { my $request = my $status = &do_something($request); return $status; }

Installation highlights Install Apache and mod_perl together Configure Apache to use mod_perl Port your CGI scripts

Installation: part 1 (The following is for Unix, Win32 installs are more difficult) Download Apache current version is Download mod_perl current version is 1.24 Check perl version (mod_perl 1.24 or earlier works best with Perl not 5.6.0)

Installation: part 2 By default building mod_perl will also build Apache > perl Makefile.PL APACHE_SRC=../apache \ DO_HTTPD=1 USE_APACI=1 EVERYTHING=1 > make;make test;make install > cd../apache ; make install

Configuration Configure Apache to use mod_perl: modify httpd.conf Include conf/perl.conf

perl.conf: part 1 PerlSetEnv PERL5LIB /my/perl/lib PerlRequire conf/startup.pl Alias /cgi-bin /my/cgi/dir PerlTaintCheck On

perl.conf: part 2 SetHandlerperl-script PerlHandlerApache::Registry OptionsExecCGI

perl.conf: part 3 A good initial check of mod_perl SetHandlerperl-script PerlHandlerApache::Status

startup.pl Loads commonly used modules Initializes database = qw( $dbh ); use lib qw( /home/matt/perl/Modules /opt/apps/lib ); my $dbh = DBI->connect($db,$user,$passwd);

Porting CGI scripts to mod_perl use strict; during porting use diagnostics; And check the error.log Run the Apache server single threaded Add the following to perl.conf PerlInitHandlerApacheStatINC

Common porting problems: part 1 As someone pointed out during the presentation, all of these problems could be solved by using re-entrant coding techniques If you used them when you wrote the CGI scripts, porting will be easy That being said, most CGI scripts are not written by people familiar with such techniques…

Common porting problems Run-time attempts to add paths Implicit variable passing Assigning anonymous sub to $SIG{__DIE__} Compiled regular expressions No closure of file or dbm handles

Adding paths This will not work is fixed after the initialization of Apache Use startup.pl to add paths BEGIN blocks only get executed at compile time

Implicit variable passing The value of the variable in subroutines will not be updated after the first call Perl considers the two variables to be separate Solutions Fully qualify the variable in the subroutine Pass by value or reference Make the variable global

$SIG{__DIE__} problems $SIG{__DIE__} is global Your anonymous subroutine will be called by any die statement Solutions Write your own exception method Error.pm (try, throw, catch)

Compiled regular expressions Only compiled for the first pattern used Solution Add an eval block eval q{ foreach { &mysub($_) if ( /$pattern/o ); }

No closure of file or dbm handles Common to use close on exit fh management Now the script does not exit…. Solution Close your file and dbm handles

Conclusions mod_perl will speed up CGI scripts by 200% to 2000% use strict; Use the PerlTaintCheck directive Effective use of mod_perl is not trivial, plan accordingly

Further Reading Writing Apache Modules with Perl and C Lincoln Stein and Doug MacEachern mod_perl Guide Stas Bekman FAQ Frank Cringle

Apache %INC hash detail The handler subroutine changes the name of the nested subroutines to the fully qualified filename plus the prefix Apache::ROOT Apache::ROOT::My::Dir::script_2epl This reduces the likelihood of namespace collisions, but frustrates tampering