Mod cluster Installation
External
- mod_cluster installation on EAP 6 in standalone mode: https://access.redhat.com/solutions/283263
- mod_cluster installation on EAP 6 in domain mode: https://access.redhat.com/solutions/173333
Internal
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. Details on httpd installation and configuration are available here: httpd installation, httpd configuration.
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 proxy_cluster_module modules/mod_proxy_cluster-1.3.1.Final.so 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 advertise_module modules/mod_advertise-1.3.1.Final.so
Insure that Module 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 Modules
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. Comment out the following line:
#LoadModule proxy_balancer_module modules/mod_proxy_balancer.so
SELinux Configuration
If SELinux it is being enforced, we will need to install additional policies to allow httpd to write mod_cluster-related files in /var/log/httpd, to perform multicast socket operations and bind on non-standard ports.
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 tcp_socket { name_bind name_connect };
class dir remove_name;
class file { write unlink };
class udp_socket name_bind;
}
#============= httpd_t ==============
allow httpd_t httpd_log_t:dir remove_name;
allow httpd_t httpd_log_t:file { write unlink };
allow httpd_t unreserved_port_t:tcp_socket { name_bind name_connect };
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 a simple httpd configuration that can be used to validate the mod_cluster installation.
The configuration declares just one virtual node that gives access to one mod_cluster manager for one balancer. For a discussion on mod_cluster balancers, managers and virtual nodes, see mod_cluster Concepts.
Listen Directive
Note that the manager is exposed on port 8088, so httpd needs to be made to listen on that port:
Listen ... Listen 1.2.3.4:8088
If the host that runs httpd has iptables enabled, you may want to open access to port 8088. Go here for more iptables configuration details.
Manager Virtual Host
Declare the mod_cluster manager virtual host. It is critical to enable MCPM receive with EnableMCPMReceive otherwise nodes won't be able to register themselves with httpd.
Note that multicast advertising is turned off and the application server nodes will have to be explicitly configured to connect to this manager.
Also note that access is allowed to all, you may want to configure stricter access rules in production.
In case you need to troubleshoot mod_cluster problems, you may want to uncomment LogLevel debug.
<VirtualHost 1.2.3.4:8088>
# LogLevel debug
<Directory />
Allow from all
</Directory>
KeepAliveTimeout 60
MaxKeepAliveRequests 0
ManagerBalancerName mycluster
EnableMCPMReceive
ServerAdvertise Off
<Location /mod_cluster-manager>
SetHandler mod_cluster-manager
Allow from all
</Location>
</VirtualHost>
<Directory /> Permissions
A default httpd installation comes with something similar to:
...
<Directory />
AllowOverride none
Require all denied
</Directory>
...
This configuration will cause trouble when mod_cluster nodes try to sent HTTP INFO / requests:
18:26:19,141 ERROR [org.jboss.modcluster] (UndertowEventHandlerAdapter - 1) MODCLUSTER000042: Error null sending INFO command to 172.20.2.41/172.20.2.41:8088, configuration will be reset: null
We need to relax the security constraints on <Directory />.
#<Directory /> # AllowOverride none # Require all denied #</Directory>
Further Configuration
More complex configurations are of course possible. For more details on how to configure mod_cluster, go to mod_cluster Configuration.
Native Component Installation on Windows
TODO, manual page 6, section 2.2.4 Install on Windows.
iptables Configuration
If iptables is enabled, make sure the multicast, MCPM, HTTP and AJP traffic are allowed on various mod_cluster hosts that need to talk to each other:
MCPM
On the httpd node, make sure MCPM inbound traffic is allowed:
-A INPUT -i eth0 -p tcp -m tcp --dport 8088 -m state --state NEW -j ACCEPT
mod_cluster Manager Port
If you chose to expose the mod_cluster manager on non-standard port, make sure the nodes have access to that port. You could open the port to everyone (non-recommended) or restrict access to that port only to the hosts that are supposed to be able to access it (recommended):
-A INPUT -i eth0 -p tcp -m tcp --dport 8088 -m state --state NEW -s 172.20.0.0/16 -j ACCEPT
HTTP and AJP Traffic
On the JBoss nodes, add this to /etc/sysconfig/iptables:
-A INPUT -i eth0 -p tcp -m tcp --dport 8080 -m state --state NEW -j ACCEPT -A INPUT -i eth0 -p tcp -m tcp --dport 8009 -m state --state NEW -j ACCEPT
Multicast Traffic
Multicast traffic should propagate from the httpd nodes to the JBoss node and maybe back? Are JBoss nodes multicasting to httpd? Research that.. Normally iptables is configured to leave all traffic out by default, so the httpd nodes should be fine. However, JBoss nodes must be enabled to allow the multicast traffic in, so add this to /etc/sysconfig/iptables:
-A INPUT -m pkttype --pkt-type multicast -j ACCEPT
More details on configuring iptables are available here: iptables configuration examples.
JBoss Components Installation
standard-ha and standard-full-ha WildFly 9 profiles come with mod_cluster enabled.
Make sure the advertise multicast address and port as the same on the httpd nodes and JBoss nodes.
Also make sure multicast propagates between httpd and the JBoss nodes (see #Multicast_Traffic).
JBoss mod_cluster Configuration
WildFly 8
TODO
This example uses uses a static proxy server list, instead of multicast httpd server advertising.
...
<subsystem xmlns="urn:jboss:domain:modcluster:1.2">
<mod-cluster-config proxy-list="10.10.10.10:6666" advertise="false" connector="ajp">
<dynamic-load-provider>
<load-metric type="busyness"/>
</dynamic-load-provider>
</mod-cluster-config>
</subsystem>
...
Dynamic:
...
<subsystem xmlns="urn:jboss:domain:modcluster:2.0">
<mod-cluster-config advertise-socket="modcluster" connector="ajp">
<dynamic-load-provider>
<load-metric type="cpu"/>
</dynamic-load-provider>
</mod-cluster-config>
</subsystem>
...
TODO: dynamic server advertising
WildFly 9
TODO
This example uses uses a static proxy server list, instead of multicast httpd server advertising.
...
<subsystem xmlns="urn:jboss:domain:modcluster:2.0">
<mod-cluster-config proxies="mod-cluster-server-1" advertise="false" connector="ajp">
<dynamic-load-provider>
<load-metric type="cpu"/>
</dynamic-load-provider>
</mod-cluster-config>
</subsystem>
...
<socket-binding-group name="standard-sockets"...>
...
<outbound-socket-binding name="mod-cluster-server-1">
<remote-destination host="172.20.2.41" port="8088"/>
</outbound-socket-binding>
</socket-binding-group>
...
TODO: dynamic server advertising
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.
Start all JBoss nodes.
Try http://httpd-virtual-host:httpd-virtual-post/mod_cluster-manager