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Appendix C. Mod_proxy_cluster connector modules
The mod_proxy_cluster
connector is a reduced-configuration, intelligent load-balancing solution based on technology that the JBoss mod_cluster community project originally developed. The mod_proxy_cluster
connector enables the Apache HTTP Server to act as an advanced load-balancer for forwarding traffic to back-end applications running on JBoss Web Server or JBoss EAP hosts. The mod_proxy_cluster
connector provides all the functionality of mod_jk
and additional features such as real-time load-balancing calculations, application life-cycle control, automatic proxy discovery, and multiple protocol support.
This appendix describes the modules that the mod_proxy_cluster
connector uses.
You can configure the mod_proxy_cluster
connector by using the configurable directives for mod_proxy
, such as ProxyIOBufferSize
.
C.1. Mod_manager.so
module and directives
The cluster manager module, mod_manager.so
, receives and acknowledges messages from nodes, including worker node registrations, worker node load data, and worker node application life cycle events.
LoadModule manager_module modules/mod_manager.so
Configurable directives for mod_manager.so
Configurable directives in the <VirtualHost>
element are as follows:
- EnableMCPMReceive
-
Allows the
VirtualHost
to receive mod_cluster management protocol (MCMP) messages. Add oneEnableMCPMReceive
directive to the Apache HTTP Server configuration to allowmod_proxy_cluster
to operate correctly.EnableMCPMReceive
must be added in theVirtualHost
configuration at the location whereadvertise
is configured. - MaxMCMPMaxMessSize
-
Defines the maximum size of MCMP messages. The default value is calculated from other
Max
directives. The minimum value is1024
. - AllowDisplay
-
Toggles the additional display on the
mod_cluster-manager
main page. The default value isoff
, which causes only version information to display on themod_cluster-manager
main page. - AllowCmd
-
Toggles permissions for commands using
mod_cluster-manager
URL. The default value ison
, which allows commands. - ReduceDisplay
-
Toggles the reduction of information displayed on the
mod_cluster-manager
page. Reducing the information allows more nodes to display on the page. The default value isoff
, which allows all the available information to display. - MemManagerFile
-
Defines the location for the files in which mod_manager stores configuration details. mod_manager also uses this location for generated keys for shared memory and lock files. This must be an absolute path name. It is recommended that this path be on a local drive, and not an NFS share. The default value is
/logs/
. - Maxcontext
-
The maximum number of contexts that
mod_proxy_cluster
will use. The default value is100
. - Maxnode
-
The maximum number of worker nodes that
mod_proxy_cluster
will use. The default value is20
. - Maxhost
-
The maximum number of hosts (aliases) that
mod_proxy_cluster
will use. This is also the maximum number of load balancers. The default value is20
. - Maxsessionid
-
The maximum number of active session identifiers stored. A session is considered inactive when no information is received from that session for five minutes. This is used for demonstration and debugging purposes only. The default value is
0
, which disables this logic. - ManagerBalancerName
-
The name of the load balancer to use when the worker node does not provide a load balancer name. The default value is
mycluster
. - PersistSlots
-
When set to
on
, nodes, aliases, and contexts are persisted in files. The default value isoff
. - CheckNonce
When set to
on
, session identifiers are checked to ensure that they are unique and have not occurred before. The default ison
.NoteSetting this directive to
off
can leave your server vulnerable to replay attacks.- SetHandler mod_cluster-manager
Defines a handler to display information about worker nodes in the cluster. This is defined in the
Location
element:<Location $LOCATION> SetHandler mod_cluster-manager Require ip 127.0.0.1 </Location>
In this situation,
$LOCATION
was also defined asmod_cluster_manager
.Consider the following guidelines when accessing the
$LOCATION
that is defined in theLocation
element in your browser:-
Transferred
corresponds to the POST data sent to the worker node. -
Connected
corresponds to the number of requests that had been processed when this status page was requested. -
Sessions
corresponds to the number of active sessions. This field is not present whenMaxsessionid
is0
.
-
C.2. Mod_proxy_cluster.so
module and directives
The Proxy Balancer Module, mod_proxy_cluster.so
, handles the routing of requests to cluster nodes. The Proxy Balancer selects the appropriate node to forward the request to based on the application location in the cluster, the current state of each of the cluster nodes, and the Session ID (if a request is part of an established session).
LoadModule proxy_cluster_module modules/mod_proxy_cluster.so
Configurable directives for mod_proxy_cluster.so
You can also configure the following directives in the <VirtualHost>
element to change the load balancing behavior.
- CreateBalancers
Defines how load balancers are created in the Apache HTTP Server virtual hosts. The following values are valid in
CreateBalancers
:-
0
: Create load balancers in all virtual hosts defined in Apache HTTP Server. Remember to configure the load balancers in theProxyPass
directive. -
1
: Do not create balancers. When using this value, you must also define the load balancer name inProxyPass
orProxyPassMatch
. -
2
: Create only the main server. This is the default value forCreateBalancers
.
-
- UseAlias
Defines whether to check that the defined
Alias
corresponds to theServerName
. The following values are valid forUseAlias
:-
0
: Ignore alias information from worker nodes. This is the default value forUseAlias
. -
1
: Verify that the defined alias corresponds to a worker node’s server name.
-
- LBstatusRecalTime
-
Defines the interval in seconds between the proxy calculating the status of a worker node. The default interval is
5
seconds. - ProxyPassMatch; ProxyPass
ProxyPass
maps remote servers into the local server namespace. If the local server has an address such ashttp://local.com/
, the followingProxyPass
directive converts a local request forhttp://local.com/requested/file1
into a proxy request forhttp://worker.local.com/file1
.ProxyPass /requested/ http://worker.local.com/
ProxyPassMatch
uses regular expressions to match local paths to which the proxied URL should apply.For either directive,
!
indicates that a specified path is local, and a request for that path should not be routed to a remote server. For example, the following directive specifies thatgif
files should be served locally.ProxyPassMatch ^(/.*\.gif)$ !
- UseNocanon
Defines whether to forward the original URL path to the back end without modifications.
The default value is
Off
. When theUseNocanon
directive is set toOff
, the proxy can forward modified URLs to the back end. However, if the back-end application expects the original URL path that the client requested, the modified URL path can lead to unexpected issues.When you set the
UseNocanon
directive toOn
, the proxy can forward the original URL path to the back end without any modifications. In this situation, the proxy behavior depends on whether you also define a context and aProxyPass
directive for the requested URL in themod_proxy_cluster.conf
file. A context is also known as a virtual host definition.Consider the following guidelines when you set the
UseNocanon
directive toOn
:-
If you define a context for the requested URL but you do not define a
ProxyPass
directive for this URL, the proxy uses theUseNocanon
directive. -
If you define both a context and a
ProxyPass
directive for the requested URL, and theProxyPass
directive includes thenocanon
flag, the proxy uses thenocanon
flag and ignores theUseNocanon
directive. -
If you define both a context and a
ProxyPass
directive for the requested URL, and theProxyPass
directive excludes thenocanon
flag, the proxy ignores theUseNocanon
directive.
NoteIf you do not define a context for the requested URL,
mod_proxy_cluster
returns a404
error.-
If you define a context for the requested URL but you do not define a
- ResponseStatusCodeOnNoContext
Defines the response status code that the server sends to the client when a
ProxyPass
orProxyPassMatch
directive does not have a matching context.The default value is
404
, which means that the server sends aNot Found
error response by default.In JBCS 2.4.51 or earlier, when a
ProxyPass
orProxyPassMatch
directive did not have a matching context, the server sent a503 Service Unavailable
response by default. If you want to preserve the default behavior that was available in earlier releases, set theResponseStatusCodeOnNoContext
directive to503
instead.NoteIf you specify a value other than a standard HTTP response code, the server access log shows the specified value but the server sends a
500 Internal Server Error
response to the client.
C.3. Mod_advertise.so
module and directives
The Proxy Advertisement Module, mod_advertise.so
, broadcasts the existence of the proxy server via UDP multicast messages. The server advertisement messages contain the IP address and port number where the proxy is listening for responses from nodes that wish to join the load-balancing cluster.
The mod_advertise
module must be defined along with the mod_manager
module in the VirtualHost
element. In the following example, the identifier for the mod_advertise
module is advertise_module
:
LoadModule advertise_module modules/mod_advertise.so
Configurable directives for mod_advertise.so
The mod_advertise
module is configurable by using the following directives:
- ServerAdvertise
Defines how the advertising mechanism is used.
The default value is
Off
. When set toOff
, the proxy does not advertise its location.When set to
On
, the advertising mechanism is used to tell worker nodes to send status information to this proxy. You can also specify a host name and port with the following syntax:ServerAdvertise On http://HOSTNAME:PORT/
. This is only required when using a name-based virtual host, or when a virtual host is not defined.- AdvertiseGroup
Defines the multicast address to advertise on. The syntax is
AdvertiseGroup ADDRESS:PORT
, whereADDRESS
must correspond toAdvertiseGroupAddress
, andPORT
must correspond toAdvertisePort
in your worker nodes.If your worker node is JBoss EAP-based, and the
-u
switch is used at startup, the defaultAdvertiseGroupAddress
is the value passed via the-u
switch.The default value is
224.0.1.105:23364
. If a port is not specified, the port defaults to23364
.- AdvertiseFrequency
-
The interval (in seconds) between multicast messages advertising the IP address and port. The default value is
10
. - AdvertiseSecurityKey
-
Defines a string that is used to identify
mod_proxy_cluster
in Apache HTTP Server. By default, this directive is not set and no information is sent. - AdvertiseManagerUrl
- Defines the URL that the worker node should use to send information to the proxy server. By default this directive is not set and no information is sent.
- AdvertiseBindAddress
-
Defines the address and port over which to send multicast messages. The syntax is
AdvertiseBindAddress ADDRESS:PORT
. This allows an address to be specified on machines with multiple IP addresses. The default value is0.0.0.0:23364
.
C.4. Mod_cluster_slotmem.so
module
The mod_cluster_slotmem.so
module is a shared memory provider for creating and accessing a shared memory segment in which the data sets are organized in "slots".
The mod_cluster_slotmem
module does not require any configuration directives.