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README.SuSE for Apache 2

For The Impatient
=================

o There are several MPM packages (MPM = multiprocessing module, which implements 
   the threads/processes model). The MPM packages contain the actual apache binary. 
   At least one MPM package must be installed.

o The apache v1 and v2 packages can be installed and run side by side :)

o Some commands have a "2" suffix, and are thus easily confused with Apache 1
   commands -- if you have an old apache (1.3) installation around.

o Edit /etc/sysconfig/apache2 to configure the list of modules to load, and other things. 
   It is no longer required to run SuSEconfig after such changes. (In fact, the
   SuSEconfig.apache2 does no longer exist.)

o For building apache modules, there are 4 apxs commands (all come with the 
   apache2-devel package):
    apxs2               builds a common module for all MPMs and installs to /usr/lib/apache2
    apxs2-prefork       builds for prefork and installs to /usr/lib/apache2-prefork
    apxs2-worker        builds for worker and installs to /usr/lib/apache2-worker

If you build apache modules, the configure script might not find apxs, and
   you'll need an option like --with-apxs=apxs2[-worker, ...], or of course you can set 
   a symlink to apxs2.

o The Apache Runtime (APR) is in the "libapr0" package (this package was named "apr" 
   in the past (8.1))

Choosing the right MPM for your application
===========================================

apache2-prefork is implemented with a prefork regime, while
apache2-worker uses a hybrid threaded/preforked model.

Which one to use? The short answer is: 
 - if in doubt, simply use prefork
 - use prefork if you use mod_php4
 - use worker if you need maximal performance with (possibly) less resources
   (smaller memory footprint of threade compared to the same number as processes)

The following nice article has a more in depth answer:
http://www.onlamp.com/pub/a/apache/2004/06/17/apacheckbk.html

See 
http://httpd.apache.org/docs/2.4/mpm.html  and
http://httpd.apache.org/docs/2.4/misc/perf-tuning.html#compiletime 
for more technical details.

In general, using a threaded MPM (worker) requires that all libraries that are
loaded into apache (and libraries loaded by them in turn) be threadsafe as well.
See
http://httpd.apache.org/docs/2.4/developer/thread_safety.html for a status on
some libraries.

Upgrading from apache 1.3
=========================

For a smooth transition from apache 1.3, apache 2 is installable alongside apache
1.3. There are a few modules for apache 1 that have not been ported or enough
tested for apache 2, but most important modules are available by now.

The mechanism of specifying modules to load into the server has been cleaned up
so a reasonable default set of modules is loaded. (It is not useful to load all
available modules by default, it would make the server quite big and slow. This
is important given as the number of modules in the apache base distribution is
rising and rising (about 50 at this time).

In previous apache packages (1.3), modules were activated by setting a
APACHE_MOD_XYZ variable to "yes" and running SuSEconfig.
Nowadays, modules are activated by adding them to a the APACHE_MODULES
variable in /etc/sysconfig/apache2, and simply restarting apache.

Building modules for apache 2
=============================

Therefore, the different MPMs will be needed and a mechanism to build
the modules spesific to them.  This can now be done with the apxs2, 
apxs2-worker or apxs2-prefork script.

For a module's configure script, you would typically use
 --which-apxs=/usr/sbin/apxs2-prefork

In RPM spec files, you can use
  %define apxs apxs2
  %define apache_libexecdir %(%{apxs} -q libexecdir)
to build modules, or use apxs2-prefork (for instance) to build a module
specifically for the prefork MPM.

To further the example, apxs2-prefork will install a module below
/usr/lib/apache2-prefork/, while "apxs2" will install it below
/usr/lib/apache2/.

-a adds the module to APACHE_MODULES in /etc/sysconfig/apache2, which in turn
takes care of loading the module.

Thus, usually you will only have to call
 apxs2 -cia my_module.c
and all is fine.

-- 
Suggestions or bug reports (via http://bugzilla.novell.com/) are most
welcome.

Mar 14 2005, Peter Poeml

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