Using Apache httpd 2.4 on Red Hat Enterprise Linux 6

For a long time one of the most frequent requests from users of Apache httpd on Red Hat Enterprise Linux 6 has been "Why aren't you shipping Apache 2.4 yet?". Well, the good news is: we are! There are actually two ways for Red Hat Enterprise Linux users to get httpd 2.4. The first is to upgrade to RHEL 7, which comes with httpd 2.4.6 natively.

The second is to use Red Hat Software Collections on RHEL 6, and that's what I'm going to talk about in this blog post. First up, how to get the bits?

Enable the RHSCL Repository

Most RHEL subscriptions will allow you to Red Hat Software Collections repositories. If not, contact Customer Service! I used a fresh RHEL 6 Server virtual machine to demonstrate this:

[root@virt-el6scratch ~]# yum repolist all | grep rhscl
This system is receiving updates from Red Hat Subscription Management.
rhel-server-rhscl-6-beta-debug-rpms                   Red Hat So disabled
...
rhel-server-rhscl-6-rpms                              Red Hat So disabled
rhel-server-rhscl-6-source-rpms                       Red Hat So disabled

Those are the the RHSCL channels... we only need to enable one here:

[root@virt-el6scratch ~]# yum-config-manager --enable rhel-server-rhscl-6-rpms
...

If that command produces a long yum configuration on your terminal, it was successful.

Install the packages

Here, we are going to install the httpd package from the httpd24
software collection - RHSCL packages are named <scl>-<pkg>, so the
command is:

[root@virt-el6scratch ~]# yum install -y -q httpd24-httpd
...
Installed:
  httpd24-httpd.x86_64 0:2.4.6-18.el6

Dependency Installed:
  httpd24-apr.x86_64 0:1.4.8-3.el6         httpd24-apr-util.x86_64 0:1.5.2-7.el6       httpd24-httpd-tools.x86_64 0:2.4.6-18.el6
  httpd24-runtime.x86_64 0:1.1-4.el6

That's the minimal needed for an httpd 2.4 installation. Here I've installed the httpd package, which includes many of the bundled modules. Some larger modules, or those which pull in bigger sets of dependencies are packaged separatetely. The set of httpd module packages we have in the httpd24 SCL is as follows:

[root@virt-el6scratch ~]# yum list -C httpd24-mod_*
This system is receiving updates from Red Hat Subscription Management.
Available Packages
httpd24-mod_auth_kerb.x86_64                                   5.4-29.el6                                       rhel-server-rhscl-6-rpms
httpd24-mod_ldap.x86_64                                        2.4.6-18.el6                                     rhel-server-rhscl-6-rpms
httpd24-mod_proxy_html.x86_64                                  1:2.4.6-18.el6                                   rhel-server-rhscl-6-rpms
httpd24-mod_session.x86_64                                     2.4.6-18.el6                                     rhel-server-rhscl-6-rpms
httpd24-mod_ssl.x86_64                                         1:2.4.6-18.el6                                   rhel-server-rhscl-6-rpms

That includes the third-party Kerberos authentication module, mod_auth_kerb. In Red Hat Software Collections v1.1 we also have mod_wsgi, mod_perl, mod_passenger, and PHP 5.5, which can all be used with the httpd 2.4 collection.

Init scripts in RHSCL packages are named using the same convention as above, so to start the daemon:

[root@virt-el6scratch ~]# service httpd24-httpd start
Starting httpd:                                            [  OK  ]
[root@virt-el6scratch ~]# curl --silent http://localhost/ | grep 'Red Hat' | head -1
Test Page for the Apache HTTP Server on Red Hat Enterprise Linux

It works!

One of the features of 2.4 which users have been asking for is the "event" Multi-Processing Module. In httpd there are various MPMs available which allow different processing models to be used by the server; the default, traditional process-based server is "prefork". The event MPM is a threaded model with some specific enhancements
for handling idle connections, which was shipped experimentally in httpd 2.2 but is fully supported in 2.4.

For anybody who has tried configuring a different MPM in httpd 2.2
before, a different method is used in 2.4. With httpd 2.2, separate
MPMs were shipped by compiling the "/usr/sbin/httpd" binary multiple times,
so "/usr/sbin/httpd.worker" was a replacement httpd binary which used
the threaded "worker" MPM.

In 2.4, MPMs are now loadable modules. To enable the event MPM with the httpd24 software collection, edit the configuration file /opt/rh/httpd24/root/etc/httpd/conf.modules.d/00-mpm.conf, comment-out the line for the prefork module, and uncomment the line which loads the right module:

LoadModule mpm_event_module modules/mod_mpm_event.so

Here it is in action:

[root@virt-el6scratch ~]# service httpd24-httpd start
Starting httpd:                                            [  OK  ]
[root@virt-el6scratch ~]# grep resuming /var/log/httpd24/error_log | tail -1
[Tue Sep 23 12:12:41.319368 2014] [mpm_event:notice] [pid 31774:tid 140410273740768] AH00489: Apache/2.4.6 (Red Hat) configured -- resuming normal operations

Looking carefully at that log message, the "mpm_event" prefix used shows that the event MPM has indeed being activated.  Another way to verify is to run "httpd" from the SCL:

[root@virt-el6scratch ~]# scl enable httpd24 'httpd -V'
Server version: Apache/2.4.6 (Red Hat)
Server built:   Jul 18 2014 06:22:09
Server's Module Magic Number: 20120211:23
Server loaded:  APR 1.4.8, APR-UTIL 1.5.2
Compiled using: APR 1.4.8, APR-UTIL 1.5.2
Architecture:   64-bit
Server MPM:     event
  threaded:     yes (fixed thread count)
    forked:     yes (variable process count)

Again, this shows the threaded "event" MPM is active.

For more information about Red Hat Software Collections or Red Hat Developer Toolset, visit https://developers.redhat.com/products/rhel/overview.