NAME

mod_perl 2.0 Server Configuration

Description

This chapter provides an indepth mod_perl 2.0 configuration details.

mod_perl configuration directives

Similar to mod_perl 1.0, in order to use mod_perl 2.0 a few configuration settings should be added to httpd.conf. They are quite similar to 1.0 settings but some directives were renamed and new directives were added.

Enabling mod_perl

To enable mod_perl built as DSO add to httpd.conf:

LoadModule perl_module modules/mod_perl.so

This setting specifies the location of the mod_perl module relative to the ServerRoot setting, therefore you should put it somewhere after ServerRoot is specified.

If mod_perl has been statically linked it's automatically enabled.

Perl's Command Line Switches

Now you can pass any Perl's command line switches in httpd.conf using the PerlSwitches directive. For example to enable warnings and Taint checking add:

PerlSwitches -wT

As an alternative to using use lib in startup.pl to adjust @INC, now you can use the command line switch -I to do that:

PerlSwitches -I/home/stas/modperl

You could also use -Mlib=/home/stas/modperl which is the exact equivalent as use lib, but it's broken on certain platforms/version (e.g. Darwin/5.6.0). use lib is removing duplicated entries, whereas -I does not.

PerlOptions Directive

The directive PerlOptions provides fine-grained configuration for what were compile-time only options in the first mod_perl generation. It also provides control over what class of PerlInterpreter is used for a <VirtualHost> or location configured with <Location>, <Directory>, etc.

Options are enabled by prepending + and disabled with -. The options include:

`Enable`

On by default, can be used to disable mod_perl for a given VirtualHost. For example:

<VirtualHost ...>
    PerlOptions -Enable
</VirtualHost>

`Clone`

Share the parent Perl interpreter, but give the VirtualHost its own interpreter pool. For example should you wish to fine tune interpreter pools for a given virtual host:

<VirtualHost ...>
    PerlOptions +Clone
    PerlInterpStart 2
    PerlInterpMax 2
</VirtualHost>

This might be worthwhile in the case where certain hosts have their own sets of large-ish modules, used only in each host. By tuning each host to have its own pool, that host will continue to reuse the Perl allocations in their specific modules.

When cloning a Perl interpreter, to inherit base Perl interpreter's PerlSwitches use:

<VirtualHost ...>
    ...
    PerlSwitches +inherit
</VirtualHost>

`Parent`

Create a new parent Perl interpreter for the given VirtualHost and give it its own interpreter pool (implies the Clone option).

A common problem with mod_perl 1.0 was the shared namespace between all code within the process. Consider two developers using the same server and each wants to run a different version of a module with the same name. This example will create two parent Perl interpreters, one for each <VirtualHost>, each with its own namespace and pointing to a different paths in @INC:

<VirtualHost ...>
    ServerName dev1
    PerlOptions +Parent
    PerlSwitches -Mblib=/home/dev1/lib/perl
</VirtualHost>

<VirtualHost ...>
    ServerName dev2
    PerlOptions +Parent
    PerlSwitches -Mblib=/home/dev2/lib/perl
</VirtualHost>

Or even for a given location, for something like "dirty" cgi scripts:

<Location /cgi-bin>
    PerlOptions +Parent
    PerlInterpMaxRequests 1
    PerlInterpStart 1
    PerlInterpMax 1
    PerlResponseHandler ModPerl::Registry
</Location>

will use a fresh interpreter with its own namespace to handle each request.

`Perl*Handler`

Disable Perl*Handlers, all compiled-in handlers are enabled by default. The option name is derived from the Perl*Handler name, by stripping the Perl and Handler parts of the word. So PerlLogHandler becomes Log which can be used to disable PerlLogHandler:

PerlOptions -Log

Suppose one of the hosts does not want to allow users to configure PerlAuthenHandler, PerlAuthzHandler, PerlAccessHandler and <Perl> sections:

<VirtualHost ...>
    PerlOptions -Authen -Authz -Access -Sections
</VirtualHost>

Or maybe everything but the response handler:

<VirtualHost ...>
    PerlOptions None +Response
</VirtualHost>

`AutoLoad`

Resolve Perl*Handlers at startup time, which includes loading the modules from disk if not already loaded.

In mod_perl 1.0, configured Perl*Handlers which are not a fully qualified subroutine names are resolved at request time, loading the handler module from disk if needed. In mod_perl 2.0, configured Perl*Handlers are resolved at startup time. By default, modules are not auto-loaded during startup-time resolution. It is possible to enable this feature with:

PerlOptions +Autoload

Consider this configuration:

PerlResponseHandler Apache::Magick

In this case, Apache::Magick is the package name, and the subroutine name will default to handler. If the Apache::Magick module is not already loaded, PerlOptions +Autoload will attempt to pull it in at startup time. With this option enabled you don't have to explicitly load the handler modules. For example you don't need to add:

PerlModule Apache::Magick

in our example.

`GlobalRequest`

Setup the global request_rec for use with Apache->request. This setting is needed for example if you use CGI.pm to process the incoming request.

This setting is enabled by default for sections configured as:

<Location ...>
    SetHandler perl-script
    ...
</Location>

And can be disabled with:

<Location ...>
    SetHandler perl-script
    PerlOptions -GlobalRequest
    ...
</Location>

`ParseHeaders`

Scan output for HTTP headers, same functionality as mod_perl 1.0's PerlSendHeaders, but more robust. This option is usually needs to be enabled for registry scripts which send the HTTP header with:

print "Content-type: text/html\n\n";

`MergeHandlers`

Turn on merging of Perl*Handler arrays. For example with a setting:

PerlFixupHandler Apache::FixupA

<Location /inside>
    PerlFixupHandler Apache::FixupB
</Location>

a request for /inside only runs Apache::FixupB (mod_perl 1.0 behavior). But with this configuration:

PerlFixupHandler Apache::FixupA

<Location /inside>
    PerlOptions +MergeHandlers
    PerlFixupHandler Apache::FixupB
</Location>

a request for /inside will run both Apache::FixupA and Apache::FixupB handlers.

`SetupEnv`

Set up enviroment variables for each request ala mod_cgi.

When this option is enabled, mod_perl fiddles with the environment to make it appear as if the code is called under the mod_cgi handler. For example, the $ENV{QUERY_STRING} environment variable is initialized with the contents of Apache::args(), and the value returned by Apache::server_hostname() is put into $ENV{SERVER_NAME}.

But %ENV population is expensive. Those who have moved to the Perl Apache API no longer need this extra %ENV population, and can gain by disabling it. A code using the CGI.pm module require PerlOptions +SetupEnv because that module relies on a properly populated CGI environment table.

This option is enabled by default for sections configured as:

<Location ...>
    SetHandler perl-script
    ...
</Location>

Since this option adds an overhead to each request, if you don't need this functionality you can turn it off for a certain section:

<Location ...>
    SetHandler perl-script
    PerlOptions -SetupEnv
    ...
</Location>

or globally:

PerlOptions -SetupEnv
<Location ...>
    ...
</Location>

and then it'll affect the whole server. It can still be enabled for sections that need this functionality.

When this option is disabled you can still read environment variables set by you. For example when you use the following configuration:

PerlOptions -SetupEnv
PerlModule Modperl::Registry
<Location /perl>
  PerlSetEnv TEST hi
  SetHandler perl-script
  PerlHandler ModPerl::Registry
  Options +ExecCGI
</Location>

and you issue a request for this script:

setupenvoff.pl
--------------
use Data::Dumper;
my $r = Apache->request();
$r->send_http_header('text/plain');
print Dumper(\%ENV);

you should see something like this:

$VAR1 = {
          'GATEWAY_INTERFACE' => 'CGI-Perl/1.1',
          'MOD_PERL' => 'mod_perl/2.0.1',
          'PATH' => 'bin:/usr/bin',
          'TEST' => 'hi'
        };

Notice that we have got the value of the environment variable TEST.

Handlers Directives

META: need to add descriptions

PerlChildInitHandler

PerlOpenLogsHandler

PerlPostConfigHandler

PerlPreConnectionHandler

PerlProcessConnectionHandler

PerlHeaderParserHandler

PerlAccessHandler

PerlAuthenHandler

PerlAuthzHandler

PerlTypeHandler

PerlFixupHandler

PerlResponseHandler

PerlLogHandler

PerlPostReadRequestHandler

PerlInitHandler

PerlTransHandler

PerlOutputFilterHandler

The mod_perl 2.0 interface to the Apache filtering API is much simpler than the C API, hiding most of the details underneath. Perl filters are configured using the PerlOutputFilterHandler directive. For example:

PerlOutputFilterHandler Apache::ReverseFilter

This simply registers the filter, which can then be turned on using the core AddOutputFilter directive:

<Location /filterme>
    AddOutputFilter Apache::ReverseFilter
</Location>

The Apache::ReverseFilter handler will now be called for anything accessed in the /filterme URL space. The AddOutputFilter directive takes any number of filters. For example, the configuration:

AddOutputFilter INCLUDE Apache::ReverseFilter

will first send the output to mod_include, which will in turn pass its output down to Apache::ReverseFilter.

Threads Mode Specific Directives

These directives are enabled only in a threaded mod_perl+Apache combo:

`PerlInterpStart`

The number of intepreters to clone at startup time.

`PerlInterpMax`

If all running interpreters are in use, mod_perl will clone new interpreters to handle the request, up until this number of interpreters is reached. when PerlInterpMax is reached, mod_perl will block (via COND_WAIT()) until one becomes available (signaled via COND_SIGNAL()).

`PerlInterpMinSpare`

The minimum number of available interpreters this parameter will clone interpreters up to PerlInterpMax, before a request comes in.

`PerlInterpMaxSpare`

mod_perl will throttle down the number of interpreters to this number as those in use become available.

`PerlInterpMaxRequests`

The maximum number of requests an interpreter should serve, the interpreter is destroyed when the number is reached and replaced with a fresh clone.

`PerlInterpScope`

As mentioned, when a request in a threaded mpm is handled by mod_perl, an interpreter must be pulled from the interpreter pool. The interpreter is then only available to the thread that selected it, until it is released back into the interpreter pool. By default, an interpreter will be held for the lifetime of the request, equivalent to this configuration:

PerlInterpScope request

For example, if a PerlAccessHandler is configured, an interpreter will be selected before it is run and not released until after the logging phase.

Intepreters will be shared across subrequests by default, however, it is possible to configure the intepreter scope to be per-subrequest on a per-directory basis:

PerlInterpScope subrequest

With this configuration, an autoindex generated page, for example, would select an interpreter for each item in the listing that is configured with a Perl*Handler.

It is also possible to configure the scope to be per-handler:

PerlInterpScope handler

With this configuration, an interpreter will be selected before PerlAccessHandlers are run, and putback immediately afterwards, before Apache moves onto the authentication phase. If a PerlFixupHandler is configured further down the chain, another interpreter will be selected and again putback afterwards, before PerlResponseHandler is run.

For protocol handlers, the interpreter is held for the lifetime of the connection. However, a C protocol module might hook into mod_perl (e.g. mod_ftp) and provide a request_rec record. In this case, the default scope is that of the request. Should a mod_perl handler want to maintain state for the lifetime of an ftp connection, it is possible to do so on a per-virtualhost basis:

PerlInterpScope connection

mod_perl Directives Argument Types and Allowed Location

The following table shows where in the configuration files mod_perl configuration directives are allowed to appear, what kind of and how many arguments they expect:

General directives:

  Directive                 Arguments     SRV   DIR
---------------------------------------------------
PerlSwitches                 ITERATE       V
PerlRequire                  ITERATE       V
PerlModule                   ITERATE       V
PerlOptions                  ITERATE       V     V
PerlSetVar                   TAKE2         V     V
PerlAddVar                   ITERATE2      V     V
PerlSetEnv                   TAKE2         V     V
PerlPassEnv                  TAKE1         V
<Perl> Sections              RAW_ARGS      V
PerlTrace                    TAKE1         V

Handler assignment directives:

  Directive                 Arguments  TYPE     SRV   DIR
---------------------------------------------------------
PerlOpenLogsHandler          ITERATE  RUN_ALL    V
PerlPostConfigHandler        ITERATE  RUN_ALL    V
PerlChildInitHandler         ITERATE  VOID       V

PerlPreConnectionHandler     ITERATE  RUN_ALL    V
PerlProcessConnectionHandler ITERATE  RUN_FIRST  V

PerlPostReadRequestHandler   ITERATE  RUN_ALL    V
PerlTransHandler             ITERATE  RUN_FIRST  V
PerlInitHandler              ITERATE  RUN_ALL    V     V
PerlHeaderParserHandler      ITERATE  RUN_ALL    V     V
PerlAccessHandler            ITERATE  RUN_ALL    V     V
PerlAuthenHandler            ITERATE  RUN_FIRST  V     V
PerlAuthzHandler             ITERATE  RUN_FIRST  V     V
PerlTypeHandler              ITERATE  RUN_FIRST  V     V
PerlFixupHandler             ITERATE  RUN_ALL    V     V
PerlResponseHandler          ITERATE  RUN_FIRST  V     V
PerlLogHandler               ITERATE  RUN_ALL    V     V
PerlCleanupHandler           ITERATE  XXX        V     V

PerlInputFilterHandler       ITERATE  VOID       V     V
PerlOutputFilterHandler      ITERATE  VOID       V     V

Perl Interpreter management directives:

  Directive                 Arguments     SRV   DIR
---------------------------------------------------
PerlInterpStart              TAKE1         V
PerlInterpMax                TAKE1         V
PerlInterpMinSpare           TAKE1         V
PerlInterpMaxSpare           TAKE1         V
PerlInterpMaxRequests        TAKE1         V
PerlInterpScope              TAKE1         V     V

mod_perl 1.0 back compatibility directives:

  Directive                 Arguments     SRV   DIR
---------------------------------------------------
PerlHandler                   ITERATE      V     V
PerlSendHeader                FLAG         V     V
PerlSetupEnv                  FLAG         V     V
PerlTaintCheck                FLAG         V
PerlWarn                      FLAG         V

The Arguments column represents the type of arguments directives accepts, where:

ITERATE: Expects a list of arguments.
ITERATE2: Expects one argument, followed by at least one or more arguments.
TAKE1: Expects one argument only.
TAKE2: Expects two arguments only.
FLAG: One of On or Off (case insensitive).
RAW_ARGS: The function parses the command line by itself.

The second and the third column show the locations the directives are allowed to appear in:

SRV: Global configuration and <VirtualHost> (mnemonic: SeRVer). These directives are defined as RSRC_CONF in the source code.
DIR: <Directory>, <Location>, <Files> and all their regex variants (mnemonic: DIRectory). These directives can also appear in .htaccess files. These directives are defined as OR_ALL in the source code.

Apache specifies other allowed location types which are currently not used by the core mod_perl directives and their definition can be found in include/httpd_config.h (hint: search for RSRC_CONF).

Server Startup Options Retrieval

Inside httpd.conf one can do conditional configuration based on the define options passed at the server startup. For example:

<IfDefine PERLDB>
    <Perl>
        use Apache::DB ();
        Apache::DB->init;
    </Perl>
  
    <Location />
        PerlFixupHandler Apache::DB
    </Location>
</IfDefine>

So only when the server is started as:

% httpd C<-DPERLDB> ...

The configuration inside IfDefine will have an effect. If you want to have some configuration section to have an effect if a certain define wasn't defined use !, for example here is the opposite of the previous example:

<IfDefine !PERLDB>
    # ...
</IfDefine>

If you need to access any of the startup defines in the Perl code you use Apache::exists_config_define. For example in a startup file you can say:

use Apache::ServerUtil ();
if (Apache::exists_config_define("PERLDB")) {
    require Apache::DB;
    Apache::DB->init;
}

For example to check whether the server has been started in a single mode use:

if (Apache::exists_config_define("ONE_PROCESS")) {
    print "Running in a single mode";
}

MODPERL2 Define Option

When running under mod_perl 2.0 a special configuration define MODPERL2 is enabled internally, as if the server had been started with -DMODPERL2. For example this can be used to write a configuration file which needs to do something different whether it's running under mod_perl 1.0 or 2.0:

<IfDefine MODPERL2>
    # 2.0 configuration
</IfDefine>
<IfDefine !MODPERL2>
    # else
</IfDefine>

From within Perl code this can be tested with Apache::exists_config_define(), for example:

if (Apache::exists_config_define("MODPERL2")) {
    # some 2.0 specific code
}

Debug Directives

`PerlTrace [level]`

set the trace level. This directive is enabled when mod_perl is compiled with the MP_TRACE option. level is either:

all

which sets maximum logging and debugging levels;

a combination of one or more option letters (or option numerical equivalents) from the following list:

d (  1) directive processing
f (  2) filters
g (  4) Perl runtime interaction
h (  8) handlers
i ( 16) interpreter pool management
m ( 32) memory allocations
s ( 64) perl sections
t (128) benchmark-ish timings

When level is not specified, the tracing level will be set to the value of the MOD_PERL_TRACE environment variable.

Maintainers

Maintainer is the person(s) you should contact with updates, corrections and patches.

Doug MacEachern <dougm (at) covalent.net>
Stas Bekman <stas (at) stason.org>

Authors

Doug MacEachern <dougm (at) covalent.net>

Only the major authors are listed above. For contributors see the Changes file.

To install mod_perl, copy and paste the appropriate command in to your terminal.

cpanm

cpanm mod_perl

CPAN shell

perl -MCPAN -e shell
install mod_perl

For more information on module installation, please visit the detailed CPAN module installation guide.

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