Mod cluster Installation

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Download

Compiled bundles are available here: http://mod-cluster.jboss.org/downloads

Native Components Installation on Linux

This procedure assumes httpd was already installed, configured, and it works well without mod_cluster.

At the time of the writing, the pre-compiled native components to be installed within an existing httpd are published on the download page as "mod_cluster modules for httpd". For example, the mod_cluster binaries for Linux x86 httpd are listed as "linux-x86_64 mod_cluster binaries". The file name is mod_cluster-1.3.1.Final-linux2-x64-so.tar.gz. It contains the pre-compiled httpd dynamic libraries (mod_advertise.so, mod_cluster_slotmem.so, mod_manager.so and mod_proxy_cluster.so).

Place the Dynamic Libraries in the modules Directory

Identify the httpd instance's module directory, by looking at the existing LoadModule directives specified in the configuration. It is usually /etc/httpd/modules.

It is good practice to include the mod_cluster version in the name of the dynamic library files, to make it obvious what version is used.

cp mod_advertise.so /etc/httpd/modules/mod_advertise-1.3.1.Final.so 
cp mod_cluster_slotmem.so /etc/httpd/modules/mod_cluster_slotmem-1.3.1.Final.so 
cp mod_manager.so /etc/httpd/modules/mod_manager-1.3.1.Final.so 
cp mod_proxy_cluster.so /etc/httpd/modules/mod_proxy_cluster-1.3.1.Final.so 

Make sure the newly copied files have the same ownership and permissions as the existing modules.

Load Modules at Startup

A standard RHEL httpd installation has its modules configured in /etc/httpd/conf.modules.d. All files present in that directory are automatically included from httpd.conf:

...
Include conf.modules.d/*.conf
...

Follow the same pattern to configure mod_cluster.

Add a new 99-mod_cluster.conf file in /etc/httpd/conf.modules.d with the following content:

#
# This file configures mod_cluster
#

LoadModule cluster_slotmem_module modules/mod_cluster_slotmem-1.3.1.Final.so
LoadModule manager_module modules/mod_manager-1.3.1.Final.so 
LoadModule proxy_cluster_module modules/mod_proxy_cluster-1.3.1.Final.so
LoadModule advertise_module modules/mod_advertise-1.3.1.Final.so

Insure mod_proxy Dependencies are Present and Loaded

mod_cluster needs mod_proxy to work. More details about mod_cluster dependency on mod_proxy are found here.

Make sure mod_proxy.so and mod_proxy_ajp.so are loaded. For a standard httpd installation, those modules are loaded in /etc/httpd/conf.modules.d/00-proxy.conf:

...
LoadModule proxy_module modules/mod_proxy.so
LoadModule proxy_ajp_module modules/mod_proxy_ajp.so
...

Remove undesired mod_proxy Dependencies

mod_cluster's mod_proxy_cluster cannot work correctly if mod_proxy's mod_proxy_balancer, so mod_proxy_balancer must be removed from the httpd configuration.

For a standard httpd deployment, mod_proxy_balancer is loaded in /etc/httpd/conf.modules.d/00-proxy.conf.

SELinux Configuration

If the host has SELinux enabled, we will need to install additional policies to allow httpd to write mod_cluster-related files in /var/log/httpd and also to perform multicast socket operations.

Start with a mod_cluster_1.te policy file:

module mod_cluster_1 1.0;

require {
        type httpd_log_t;
        type httpd_t;
        type unreserved_port_t;
        class file { write unlink };
        class dir remove_name;
        class udp_socket name_bind;
}

#============= httpd_t ==============
allow httpd_t httpd_log_t:dir remove_name;
allow httpd_t httpd_log_t:file unlink;
allow httpd_t httpd_log_t:file write;
allow httpd_t unreserved_port_t:udp_socket name_bind;

Compile the policy:

checkmodule -M -m -o mod_cluster_1.mod mod_cluster_1.te

Create the module package:

semodule_package -o  mod_cluster_1.pp -m mod_cluster_1.mod 

Install the policy:

semodule -i mod_cluster_1.pp

Verify that the policy was installed:

semodule -l | grep mod_cluster_1

More details about managing SELinux policies are available here: SELinux Operations.

Basic httpd.conf Configuration

This is the minimal configuration that can be used to conduct smoke tests. It consists in just one single httpd-wide balancer, accessed from the main host. More complex configurations are of course possible. For more details on how to configure mod_cluster, go to mod_cluster Configuration.

...

#
# Create a balancer available to all virtual hosts
#

CreateBalancers 0

#
# Name the balancer
#

ManagerBalancerName main

#
# Proxy a path
#

ProxyPass /proxied balancer://main/

ServerAdvertise On 

...

Native Component Installation on Windows

TODO, manual page 6, section 2.2.4 Install on Windows.

Test Initial Installation

Start httpd, it should start without warnings or errors.

mod_cluster will create a set of new files in (by default) /var/log/httpd: manager.*.slotmem and manager.*.lock.