Apache HTTP Server Connectors and Load Balancing Guide

Red Hat JBoss Core Services 2.4.29

For Use with Red Hat JBoss Core Services 2.4.29

Red Hat Customer Content Services

Abstract

This guide provides information to help users with the installation and configuration of load-balancing solutions (mod_cluster and mod_jk) along with other modules provided by Red Hat JBCS Apache HTTP Server.

Chapter 1. Introduction

This guide covers the installation and configuration of two different load balancing HTTP connectors that are included with Red Hat JBoss Core Services.

  • The Apache Tomcat Connector (mod_jk) supports the load balancing of HTTP calls to a set of Servlet containers, while maintaining sticky sessions and communicating over AJP.
  • mod_cluster is a more advanced load balancer than mod_jk, and provides all of the functionality of mod_jk, plus other additional features. These include real-time load balancing calculations, application life-cycle control, automatic proxy discovery, and multiple protocol support.

This guide also contains information on Online Certificate Status Protocol (OCSP), as well as a set of working examples for basic load balancing, and Kerberos authentication using mod_auth_kerb.

Important

Most file and directory paths shown in this guide are for a ZIP installation of JBoss Core Services on Red Hat Enterprise Linux. For other platforms, use the correct paths for your respective installation as specified in the JBoss Core Services Installation Guide.

Chapter 2. Apache Tomcat Connector (mod_jk)

The Apache Tomcat Connector, mod_jk, is a plug-in designed to allow request forwarding from Apache HTTP Server to a Servlet container. The module also supports load-balancing HTTP calls to a set of Servlet containers while maintaining sticky sessions.

2.1. Downloading and Installing mod_jk

The mod_jk module is included in the Apache HTTP Server part of a JBoss Core Services installation.

Follow the procedures in the JBoss Core Services Installation Guide to download and install Apache HTTP Server for your operating system.

2.2. Configuring Load Balancing using Apache HTTP Server and mod_jk

You can use the mod_jk connector to configure Apache HTTP Server load balancing. Follow the tasks in this section to configure load balancing using mod_jk, including configuring worker nodes.

Sample configuration files are provided for mod_jk, and are located in JBCS_HOME/httpd/conf.d/. The sample configuration files are: mod_jk.conf.sample, workers.properties.sample, and uriworkermap.properties.sample. To use these samples instead of creating your own configuration files, remove the .sample extension, and modify their content as needed.

Note

Red Hat customers can also use the Load Balancer Configuration Tool on the Red Hat Customer Portal to quickly generate optimal configuration templates for mod_jk and Tomcat worker nodes.

When using this tool for Apache HTTP Server 2.4.29, ensure you select 2.4.x as the Apache version, and select Tomcat as the back-end configuration.

2.2.1. Configuring Apache HTTP Server to load mod_jk

  1. Create a new file JBCS_HOME/httpd/conf.d/mod_jk.conf, and insert the following configuration:

    # Load mod_jk module
    # Specify the filename of the mod_jk lib
    LoadModule jk_module modules/mod_jk.so
    
    # Where to find workers.properties
    JkWorkersFile conf.d/workers.properties
    
    # Where to put jk logs
    JkLogFile logs/mod_jk.log
    
    # Set the jk log level [debug/error/info]
    JkLogLevel info
    
    # Select the log format
    JkLogStampFormat  "[%a %b %d %H:%M:%S %Y]"
    
    # JkOptions indicates to send SSL KEY SIZE
    JkOptions +ForwardKeySize +ForwardURICompat -ForwardDirectories
    
    # JkRequestLogFormat
    JkRequestLogFormat "%w %V %T"
    
    # Mount your applications
    JkMount /application/* loadbalancer
    
    # Add shared memory.
    # This directive is present with 1.2.10 and
    # later versions of mod_jk, and is needed for
    # for load balancing to work properly
    JkShmFile logs/jk.shm
    
    # Add jkstatus for managing runtime data
    <Location /jkstatus/>
        JkMount status
        Require ip 127.0.0.1
    </Location>
    Important

    The LoadModule directive must reference the mod_jk native binary you installed.

    Note

    The JkMount directive specifies which URLs that Apache HTTP Server will forward to the mod_jk module. Based on the directive’s configuration, mod_jk forwards the received URL to the correct Servlet containers.

    To enable Apache HTTP Server to serve static content (or PHP content) directly and only use the load balancer for Java applications, the suggested configuration above specifies that only requests with the URL /application/* are sent to the mod_jk load balancer.

    Alternatively, you can forward all URLs to mod_jk by specifying /* in the JkMount directive.

  2. Optional: JKMountFile Directive

    In addition to the JkMount directive, you can use the JkMountFile directive to specify a mount point’s configuration file. The configuration file contains multiple URL mappings for Tomcat forwarding.

    1. Navigate to JBCS_HOME/httpd/conf.d/ and create a file named uriworkermap.properties.
    2. Using the following syntax example as a guide, specify the URL to forward and the worker name.

      The syntax required takes the form: /URL=WORKER_NAME

      The example below configures mod_jk to forward requests for /application to the JBoss Web Server Tomcat back-end.

      # Simple worker configuration file
      
      # Mount the Servlet context to the ajp13 worker
      /application=loadbalancer
      /application/*=loadbalancer
    3. In JBCS_HOME/httpd/conf.d/mod_jk.conf , append the following directive:

      # Use external file for mount points.
      # It will be checked for updates each 60 seconds.
      # The format of the file is: /url=worker
      # /examples/*=loadbalancer
      JkMountFile conf.d/uriworkermap.properties
  3. Optional: Configure Apache HTTP Server Logging

    You can configure the Apache HTTP Server that is doing the load balancing to log which worker node handled a request. This may be useful when troubleshooting your load balancer.

    To enable this for mod_jk, you can either:

    • include %w in your JkRequestLogFormat (which is configured by default in the suggestion above) ; or
    • log the name of the mod_jk worker used by including %{JK_WORKER_NAME}n in your Apache HTTP Server LogFormat(s).

    For more information on JkRequestLogFormat, see the Apache Tomcat connector documentation. For more information on Apache HTTP Server logging (including log rotation), see the Apache HTTP Server documentation on log files.

2.2.2. Configuring Worker Nodes in mod_jk

This procedure demonstrates two mod_jk worker node definitions in a weighted round robin configuration with sticky sessions active between two servlet containers.

Prerequisites

To configure mod_jk worker nodes:

  1. Navigate to JBCS_HOME/httpd/conf.d/, and create a file named workers.properties.
  2. Add the following configuration into workers.properties, customizing it to your environment:

    # Define list of workers that will be used
    # for mapping requests
    worker.list=loadbalancer,status
    
    # Define Node1
    # modify the host as your host IP or DNS name.
    worker.node1.port=8009
    worker.node1.host=node1.mydomain.com
    worker.node1.type=ajp13
    worker.node1.ping_mode=A
    worker.node1.lbfactor=1
    
    # Define Node2
    # modify the host as your host IP or DNS name.
    worker.node2.port=8009
    worker.node2.host=node2.mydomain.com
    worker.node2.type=ajp13
    worker.node2.ping_mode=A
    worker.node2.lbfactor=1
    
    # Load-balancing behavior
    worker.loadbalancer.type=lb
    worker.loadbalancer.balance_workers=node1,node2
    worker.loadbalancer.sticky_session=1
    
    # Status worker for managing load balancer
    worker.status.type=status

2.2.3. Configuring Tomcat to work with mod_jk

Tomcat is configured to receive AJP traffic from mod_jk by default; however, there is one additional step required before you can use a worker with mod_jk. The AJP connector is configured by default in the JWS_HOME/tomcat/conf/server.xml:

<Connector port="8009" protocol="AJP/1.3" redirectPort="8443" />

In addition to the AJP enabled Connector you also need to configure a unique value for the jvmRoute attribute in the Engine of each worker node:

<Engine name="Catalina" jvmRoute="node1" >
Important

The jvmRoute attribute value must match the worker name set in workers.properties.

Chapter 3. mod_cluster Connector

3.1. Overview

The mod_cluster connector is a reduced configuration, intelligent load-balancing solution for JBoss EAP and Apache HTTP Server Tomcat, and is based on technology originally developed by the JBoss mod_cluster community project.

The mod_cluster module load-balances HTTP requests to JBoss EAP and Apache HTTP Server Tomcat worker nodes, utilizing Apache HTTP Server as the proxy server.

3.1.1. Key Features

The mod_cluster connector has several advantages over the mod_jk connector:

  • The mod_cluster Management Protocol (MCMP) is an additional connection between the Tomcat servers and the Apache HTTP Server with the mod_cluster module enabled. It is used by the Tomcat servers to transmit server-side load figures and lifecycle events back to Apache HTTP Server via a custom set of HTTP methods.
  • Dynamic configuration of Apache HTTP Server with mod_cluster allows Tomcat servers that have mod_cluster listeners to join the load balancing arrangement without manual configuration.
  • Tomcat servers perform the load calculations, rather than relying on Apache HTTP Server. This makes load balancing metrics more accurate than other connectors.
  • The mod_cluster connector gives fine-grained application lifecycle control. Each Tomcat server forwards web application context lifecycle events to the Apache HTTP Server, informing it to start or stop routing requests for a given context. This prevents end users from seeing HTTP errors due to unavailable resources.
  • AJP, HTTP, or HTTPS transports can be used.

3.1.2. Components

On the proxy server, mod_cluster consists of four Apache modules.

Table 3.1. Components

ComponentDescription

mod_cluster_slotmem.so

The Shared Memory Manager module shares real-time worker node information with multiple Apache HTTP Server processes.

mod_manager.so

The Cluster Manager module receives and acknowledges messages from worker nodes, including node registrations, node load data, and node application life cycle events.

mod_proxy_cluster.so

The Proxy Balancer Module handles request routing to cluster nodes. The Proxy Balancer selects the appropriate destination node based on 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).

mod_advertise.so

The Proxy Advertisement Module 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 server is listening for responses from worker nodes that want to join the load-balancing cluster.

See the Apache HTTP Server Modules appendix for detailed information about the available modules, including user-configurable parameters.

3.1.3. Character Limits

mod_cluster uses shared memory to keep the nodes description. The shared memory is created at the startup of Apache HTTP Server, and the structure of each item is fixed. When defining proxy server and worker node properties, ensure that you follow these character limits:

  • Maximum alias length: 100 characters (alias corresponds to the network name of the respective virtual host; the name is defined in the Host element).
  • Maximum context length: 40 characters (for example, if myapp.war is deployed in /myapp , then /myapp is included in the context).
  • Maximum balancer name length: 40 characters (the balancer property in mbean).
  • Maximum JVMRoute string length: 80 characters (JVMRoute in the <Engine> element).
  • Maximum domain name length: 20 characters (the domain property in mbean).
  • Maximum hostname length for a node: 64 characters (hostname address in the <Connector> element).
  • Maximum port length for a node: 7 characters (the port property in the <Connector> element, 8009 is 4 characters).
  • Maximum scheme length for a node: 6 characters (the protocol of the connector; possible values are http , https , ajp).
  • Maximum cookie name length: 30 characters (the header cookie name for session ID. Default value: JSESSIONID from org.apache.catalina.Globals.SESSION_COOKIE_NAME).
  • Maximum path name length: 30 characters (the parameter name for the session ID. Default value: JSESSIONID from org.apache.catalina.Globals.SESSION_PARAMETER_NAME).
  • Maximum length of a session ID: 120 characters (session ID resembles the following: BE81FAA969BF64C8EC2B6600457EAAAA.node01).

3.2. Downloading and Installing mod_cluster

The mod_cluster module is included in the Apache HTTP Server part of a JBoss Core Services installation.

Follow the procedures in the JBoss Core Services Installation Guide to download and install Apache HTTP Server for your operating system.

3.3. Configuring Load Balancing Using Apache HTTP Server and mod_cluster

In Apache HTTP Server 2.1 and higher, mod_cluster is configured correctly for Apache HTTP Server by default. To set a custom configuration, see Configuring a Basic Proxy Server.

For more information on configuring a Tomcat worker node with mod_cluster, see Configuring Worker Nodes.

Note

Red Hat customers can also use the Load Balancer Configuration Tool on the RedHat Customer Portal to quickly generate optimal configuration templates for mod_cluster, as well as Tomcat worker nodes.

When using this tool for Apache HTTP Server 2.4.29, ensure you select 2.4.x as the Apache version, and select Tomcat as the back-end configuration.

3.3.1. Configuring a Basic Proxy Server

Proxy server configuration consists of one mandatory and one optional step:

  1. Configure a Proxy Server listener to receive worker node connection requests and worker node feedback.
  2. Optional: Disable server advertisement.

Server Advertisement

The proxy server advertises itself using UDP multicast. When UDP multicast is available between the proxy server and the worker nodes, server advertisement adds worker nodes without requiring further configuration on the proxy server, and requires only minimal configuration on the worker nodes.

If UDP multicast is not available or undesirable, configure the worker nodes with a static list of proxy servers. In either case, the proxy server does not need to be configured with a list of worker nodes.

3.3.1.1. Configuring a Load-balancing Proxy Using mod_cluster

Prerequisites

  • Install Apache HTTP Server, and configure the mod_cluster modules for your installation. See the Apache HTTP Server Installation Guide for details.

To configure the load-balancing proxy using mod_cluster a Virtual Host for the management channel must be configured:

Note

This address and port combination is only for mod_cluster management messages, not general traffic.

  1. Create a Listen directive for the proxy server:

    Edit your mod_cluster configuration file (usually JBCS_HOME/httpd/conf.d/mod_cluster.conf) to add the following:

    Listen IP_ADDRESS:PORT_NUMBER

    Where IP_ADDRESS is the address of the server network interface to communicate with the worker nodes, and PORT_NUMBER is the port on that interface to listen on.

    Note

    The port must be open for incoming TCP connections.

  2. Create a virtual host:

    Add the following to your mod_cluster configuration file:

    <VirtualHost IP_ADDRESS:PORT_NUMBER>
    
       <Directory />
          Require ip IP_ADDRESS
       </Directory>
    
       KeepAliveTimeout 60
       MaxKeepAliveRequests 0
    
       ManagerBalancerName mycluster
       AdvertiseFrequency 5
       EnableMCPMReceive On
    
    </VirtualHost>

    Where IP_ADDRESS and PORT_NUMBER are the values from the Listen directive.

  3. Optional: Disable server advertisement:

    The AdvertiseFrequency directive makes the server periodically send server advertisement messages via UDP multicast. By default, this occurs every 10 seconds.

    These server advertisement messages contain the IP_ADDRESS and PORT_NUMBER specified in the VirtualHost definition. Worker nodes configured to respond to server advertisements use this information to register themselves with the proxy server.

    To disable server advertisement, add the following directive to the VirtualHost definition:

    ServerAdvertise Off

    If server advertisements are disabled, or UDP multicast is not available on the network between the proxy server and the worker nodes, configure worker nodes with a static list of proxy servers.

  4. Optional: Configure Apache HTTP Server Logging

    You can configure the Apache HTTP Server that is doing the load balancing to log which worker node handled a request. This may be useful when troubleshooting your load balancer.

    To enable this for mod_cluster, you can add the following to your Apache HTTP Server LogFormat directive(s):

    %{BALANCER_NAME}e
    The name of the balancer that served the request.
    %{BALANCER_WORKER_NAME}e
    The name of the worker node that served the request.

    For more information on Apache HTTP Server logging (including log rotation), see http://httpd.apache.org/docs/2.4/logs.html.

  5. Stop and start the Apache HTTP Server service:

    See the JBoss Core Services Installation Guide for detailed instructions.

3.3.2. Configuring Worker Nodes

3.3.2.1. Configuring a Tomcat Worker Node

Follow this procedure to install mod_cluster on a Apache HTTP Server node, and configure it for non-clustered operation.

Note

Apache HTTP Server Tomcat worker nodes only support a subset of mod_cluster functionality. Full mod_cluster functionality is available with JBoss EAP.

Supported Worker Node types

  • Apache HTTP Server Tomcat service.

mod_cluster Apache HTTP Server Node Limitations

  • Non-clustered mode only.
  • Only one load metric can be used at a time when calculating the load balance factor.

Prerequisites

To configure a Tomcat worker node:

  1. Add a listener to Tomcat:

    Add the following Listener element beneath the other Listener elements in JWS_HOME/tomcat<VERSION>/conf/server.xml.

    <Listener className="org.jboss.modcluster.container.catalina.standalone.ModClusterListener" advertise="true" stickySession="true" stickySessionForce="false" stickySessionRemove="true" />
  2. Give the worker a unique identity:

    Edit JWS_HOME/tomcat<VERSION>/conf/server.xml and add the jvmRoute attribute and value to the Engine element, as shown below:

    <Engine name="Catalina" defaultHost="localhost" jvmRoute="worker01">
  3. Configure STATUS MCMP message frequency:

    Tomcat worker nodes periodically send status messages containing their current load status to the Apache HTTP Server balancer. The default frequency of these messages is 10 seconds. If you have hundreds of worker nodes, the STATUS MCMP messages can increase traffic congestion on your Apache HTTP Server network.

    You can configure the MCMP message frequency by modifying the org.jboss.modcluster.container.catalina.status-frequency Java system property. By default, the property accepts values in seconds*10. For example, setting the property to 1 means 10 seconds. The example below demonstrates setting the frequency to 60 seconds.

    -Dorg.jboss.modcluster.container.catalina.status-frequency=6
  4. Optional: Configure the firewall for proxy server advertisements:

    A proxy server using mod_cluster can advertise itself via UDP multicast. Most operating system firewalls block this by default. To enable server advertising and receive these multicast messages, open port 23364 for UDP connections on the worker node’s firewall.

    • For Red Hat Enterprise Linux 6:

      /sbin/iptables -A INPUT -m state --state NEW -m udp -p udp --dport
       23364 -j ACCEPT
      -m comment -comment receive mod_cluster proxy server advertisements

      If automatic proxy discovery is not used, configure worker nodes with a static list of proxies. In this case you can safely ignore the following warning message:

      [warning] mod_advertise: ServerAdvertise Address or Port not defined, Advertise disabled!!!
    • For Red Hat Enterprise Linux 7:

      firewall-cmd --permanent --zone=public --add-port=23364/udp
    • For Microsoft Windows, using PowerShell

      Start-Process "$psHome\powershell.exe" -Verb Runas -ArgumentList '-command "NetSh Advfirewall firewall add rule name="UDP Port 23364" dir=in  action=allow protocol=UDP localport=23364"'
      Start-Process "$psHome\powershell.exe" -Verb Runas -ArgumentList '-command "NetSh Advfirewall firewall add rule name="UDP Port 23364" dir=out action=allow protocol=UDP localport=23364"'

3.3.2.2. Configuring a Worker Node with a Static Proxy List

Server advertisement allows worker nodes to dynamically discover and register themselves with proxy servers. If UDP multicast is not available or server advertisement is disabled, then worker nodes must be configured with a static list of proxy server addresses and ports.

Use the following procedure to configure a Apache HTTP Server worker node to operate with a static list of proxy servers.

To configure a worker node with a static proxy list:

  1. Define a mod_cluster Listener, and disable dynamic proxy discovery:

    Edit JWS_HOME/tomcat<VERSION>/conf/server.xml , and add or change the Listener element for ModClusterListener. Set the advertise property to false. For example:

    <Listener className="org.jboss.modcluster.container.catalina.standalone.ModClusterListener" advertise="false" stickySession="true" stickySessionForce="false" stickySessionRemove="true"/>
  2. Create a static proxy server list:

    Add a comma separated list of proxies to the Listener in the form of IP_ADDRESS:PORT as the proxyList property. For example:

    <Listener className="org.jboss.modcluster.container.catalina.standalone.ModClusterListener" advertise="false" stickySession="true" stickySessionForce="false" stickySessionRemove="true" proxyList="10.33.144.3:6666,10.33.144.1:6666"/>

Chapter 4. Online Certificate Status Protocol

Online Certificate Status Protocol (OCSP) is a technology which allows web browsers and web servers to communicate over a secured connection. The encrypted data is sent from one side and decrypted by the other side before processing. The web browser and the web server both encrypt and decrypt the data.

During communication with a web server, the server presents a set of credentials in the form of certificate. The browser then checks the certificate for its validity and sends a request for certificate status information. The server sends back a status as current, expired, or unknown. The certificate specifies syntax for communication and contains control information such as start time, end time, and address information to access an OCSP responder. The web server can use an OCSP responder it has been configured for, or the one listed in the certificate to check the status. OCSP allows a grace period for expired certificates, which allows access to a server for a limited time before renewing the certificate.

OCSP overcomes limitations of the older method, Certificate Revocation List (CRL). For more information on OCSP, see the Red Hat Certificate System Planning, Installation, and Deployment Guide.

4.1. Configuring Apache HTTP Server for SSL Connections

  1. Install mod_ssl using the following command:

    # yum install jbcs-httpd24-mod_ssl
  2. Edit JBCS_HOME/httpd/conf.d/ssl.conf , and add ServerName, SSLCertificateFile, and SSLCertificateKeyFile:

    <VirtualHost _default_:443>
    ServerName www.example.com:443
    SSLCertificateFile /opt/rh/jbcs-httpd24/root/etc/pki/tls/certs/localhost.crt
    SSLCertificateKeyFile /opt/rh/jbcs-httpd24/root/etc/pki/tls/private/localhost.key
    • ServerName must match the Common Name (CN) of the SSL certificate. If the ServerName does not match the CN, client browsers display domain name mismatch errors.
    • The SSLCertificateFile is the private key associated with the certificate (the public key).
    • Verify that the Listen directive in the ssl.conf file is correct as per your configuration. For example, if an IP address is specified, it must match the IP address the httpd service is bound to.
  3. Restart Apache HTTP Server using the following command:

    # service jbcs-httpd24-httpd restart

4.2. Using Online Certificate Status Protocol with Apache HTTP Server

Before you use Online Certificate Status Protocol (OCSP) for HTTPS, ensure you have configured Apache HTTP Server for SSL connections.

To use OCSP with Apache HTTP Server, ensure that a Certificate Authority (CA) and OCSP Responder are configured correctly.

For more information on how to configure a CA, see the Managing Certificates and Certificate Authorities section in the Red Hat Enterprise Linux 7 Linux Domain Identity, Authentication, and Policy Guide.

For more information on how to configure an OCSP Responder, see the Configuring OCSP Responders section in the Red Hat Enterprise Linux 7 Linux Domain Identity, Authentication, and Policy Guide.

Note

Ensure that your Certificate Authority is capable of issuing OCSP certificates. The Certificate Authority must be able to append the following attributes to the certificate:

[ usr_cert ]
...
authorityInfoAccess=OCSP;URI:http://HOST:PORT
...
[ v3_OCSP ]
basicConstraints = CA:FALSE
keyUsage = nonRepudiation, digitalSignature, keyEncipherment
extendedKeyUsage = OCSP Signing

Note that HOST and PORT will need to be replaced with the details of the OCSP responder that you will configure.

4.3. Configuring Apache HTTP Server to Validate OCSP Certificates

Before configuring Apache HTTP Server to validate OCSP certificates, ensure that a Certificate Authority (CA) and an OCSP Responder is configured correctly. The example below shows how to enable OCSP validation of client certificates.

Use the SSLOCSPEnable attribute to enable OCSP validation:

# Require valid client certificates (mutual auth)
  SSLVerifyClient require
  SSLVerifyDepth  3
  # Enable OCSP
  SSLOCSPEnable on
  SSLOCSPDefaultResponder http://10.10.10.25:3456
  SSLOCSPOverrideResponder on

4.4. Verifying Your OCSP Configuration

You can use the OpenSSL command-line tool to verify your configuration:

# openssl ocsp -issuer cacert.crt -cert client.cert -url http://HOST:PORT -CA ocsp_ca.cert -VAfile ocsp.cert
  • -issuer is the Certificate Authority certificate.
  • -cert is the client certificate which you want to verify.
  • -url is the HTTP server validating Certificate (OCSP).
  • -CA is the CA certificate for verifying the Apache HTTP Server server certificate.
  • -VAfile is the OCSP responder certificate.

Chapter 5. Complete Working Examples

5.1. mod_cluster Example

This section contains a set of example configurations for a complete working example of how to use mod_cluster on a Red Hat Enterprise Linux system.

Load Balancer

To setup JBoss Core Services as a proxy server listening on localhost, create a configuration file in JBCS_HOME/httpd/conf.d/mod_cluster.conf and add the following:

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

MemManagerFile cache/mod_cluster

<IfModule manager_module>
  Listen 6666
  <VirtualHost *:6666>
    <Directory />
      Require ip 127.0.0.1
    </Directory>
    ServerAdvertise on
    EnableMCPMReceive
    <Location /mod_cluster_manager>
      SetHandler mod_cluster-manager
      Require ip 127.0.0.1
   </Location>
  </VirtualHost>
</IfModule>

Worker Configuration for Tomcat

Edit JWS_HOME/tomcat/conf/server.xml, and add the following Listener element to configure a Tomcat worker node:

<Listener className="org.jboss.modcluster.container.catalina.standalone.ModClusterListener" advertise="true"/>

Example iptables Firewall Rules

The following are a set of example firewall rules using iptables, for a cluster node on the 192.168.1.0/24 subnet.

/sbin/iptables -I INPUT 5 -p udp -d 224.0.1.0/24 -j ACCEPT -m comment --comment "mod_cluster traffic"
/sbin/iptables -I INPUT 6 -p udp -d 224.0.0.0/4 -j ACCEPT -m comment --comment "JBoss Cluster traffic"
/sbin/iptables -I INPUT 9 -p udp -s 192.168.1.0/24 -j ACCEPT -m comment --comment "cluster subnet for inter-node communication"
/sbin/iptables -I INPUT 10 -p tcp -s 192.168.1.0/24 -j ACCEPT -m comment --comment "cluster subnet for inter-node communication"
/etc/init.d/iptables save

5.2. mod_auth_kerb Example

This section contains instructions for a basic example for configuring Kerberos authentication with JBoss Core Services' Apache HTTP Server and mod_auth_kerb on Red Hat Enterprise Linux.

5.2.1. mod_auth_kerb Example Prerequisites

The following is a list of prerequisites for the working example. Ensure that all prerequisites are met before attempting to use the example instructions.

  • Install curl with GSS-negotiated support (for testing the configuration).
  • Configure and run a Kerberos or LDAP server (for example ApacheDS) on the same host as JBoss Core Services.
  • If using an LDAP server, create the following LDAP users:

    • Create the user krbtgt:

      dn: uid=krbtgt,ou=Users,dc=example,dc=com
      objectClass: top
      objectClass: person
      objectClass: inetOrgPerson
      objectClass: krb5principal
      objectClass: krb5kdcentry
      cn: KDC Service
      sn: Service
      uid: krbtgt
      userPassword: secret
      krb5PrincipalName: krbtgt/EXAMPLE.COM@EXAMPLE.COM
      krb5KeyVersionNumber: 0
    • Create the user ldap:

      dn: uid=ldap,ou=Users,dc=example,dc=com
      objectClass: top
      objectClass: person
      objectClass: inetOrgPerson
      objectClass: krb5principal
      objectClass: krb5kdcentry
      cn: LDAP
      sn: Service
      uid: ldap
      userPassword: randall
      krb5PrincipalName: ldap/localhost@EXAMPLE.COM
      krb5KeyVersionNumber: 0
    • Create the user HTTP:

      dn: uid=HTTP,ou=Users,dc=example,dc=com
      objectClass: top
      objectClass: person
      objectClass: inetOrgPerson
      objectClass: krb5principal
      objectClass: krb5kdcentry
      cn: HTTP
      sn: Service
      uid: HTTP
      userPassword: secretpwd
      krb5PrincipalName: HTTP/localhost@EXAMPLE.COM
      krb5KeyVersionNumber: 0
    • Create user hnelson (test user):

      dn: uid=hnelson,ou=Users,dc=example,dc=com
      objectClass: top
      objectClass: person
      objectClass: inetOrgPerson
      objectClass: krb5principal
      objectClass: krb5kdcentry
      cn: Horatio Nelson
      sn: Nelson
      uid: hnelson
      userPassword: secret
      krb5PrincipalName: hnelson@EXAMPLE.COM
      krb5KeyVersionNumber: 0

5.2.2. Configure the Kerberos Client

  1. Create the krb5.conf configuration file in the /etc directory, and add the following to the file:

    [logging]
      default = FILE:/var/log/krb5libs.log
      kdc = FILE:/var/log/krb5kdc.log
      admin_server = FILE:/var/log/kadmind.log
    
    [libdefaults]
      default_realm = EXAMPLE.COM
      default_tgs_enctypes = des-cbc-md5,des3-cbc-sha1-kd
      default_tkt_enctypes = des-cbc-md5,des3-cbc-sha1-kd
      dns_lookup_realm = false
      dns_lookup_kdc = false
      allow_weak_crypto = yes
      ticket_lifetime = 24h
      renew_lifetime = 7d
      forwardable = yes
    
    [realms]
      EXAMPLE.COM = {
        kdc = localhost:60088
        admin_server = localhost:60088
      }
    
    [domain_realm]
      .example.com = EXAMPLE.COM
      example.com = EXAMPLE.COM
  2. Create a key tab in the JBCS_HOME/httpd/conf folder with the following contents:

    # ktutil
    ktutil: addent -password -p HTTP/localhost@EXAMPLE.COM -k 0 -e des-cbc-md5
    Password for HTTP/localhost@EXAMPLE.COM: secretpwd
    ktutil: list
    slot KVNO Principal
    ---- ---- ---------------------------------------------------------------------
       1    0               HTTP/localhost@EXAMPLE.COM
    ktutil: wkt JBCS_HOME/httpd/conf/krb5.keytab
    ktutil: quit
Important

Environment variables are not expanded within the ktutil prompt. Users will need to substitute the full path for the JBCS_HOME variable.

As the root user, run the following commands to apply the correct group and permissions to the key tab:

# chgrp apache JBCS_HOME/httpd/conf/krb5.keytab
# chmod 640 JBCS_HOME/httpd/conf/krb5.keytab
  1. Ensure that the following host configuration is included in the /etc/hosts file:

    127.0.0.1 localhost

5.2.3. Configure mod_auth_kerb

Create the auth_kerb.conf configuration file in the JBCS_HOME/httpd/conf.d/ folder, and add the following configuration to the file:

#
# The mod_auth_kerb module implements Kerberos authentication over HTTP, following the "Negotiate" protocol.
#

# The LoadModule statement is done in conf.d/10-auth_kerb.conf
# LoadModule auth_kerb_module modules/mod_auth_kerb.so

<Location /kerberostest>
  AuthType Kerberos
  AuthName "Kerberos Login"
  KrbMethodNegotiate On
  KrbMethodK5Passwd Off
  KrbAuthRealms EXAMPLE.COM
  KrbServiceName HTTP
  Krb5KeyTab $JBCS_HOME/httpd/krb5.keytab
  require valid-user
</Location>
Important

Environment variables are not expanded within the configuration files. Users will need to substitute the full path for the JBCS_HOME variable.

5.2.4. Test the Kerberos Authentication

  1. Create a test page named auth_kerb_page.html in JBCS_HOME/httpd/www/html/kerberostest/.
  2. Add the following contents to the test page (auth_kerb_page.html):

    <html>
    <body>
        <h1>mod_auth_kerb successfully authenticated!</h1>
    </body>
    </html>
  3. Optional: Set the log level for debugging in JBCS_HOME/httpd/conf/httpd.conf.
  4. Start Apache HTTP Server. See the Installation Guide for details.
  5. Test the authentication as follows:

    1. Initiate Kerberos authentication for the test user hnelson:

      $ kinit hnelson
    2. View the details for the test user hnelson:

      $ klist

      A result similar to the following appears:

      Ticket cache: FILE:/tmp/krb5cc_18602
      Default principal: hnelson@EXAMPLE.COM
      
      Valid starting     Expires            Service principal
      06/03/13 14:21:13  06/04/13 14:21:13  krbtgt/EXAMPLE.COM@EXAMPLE.COM
      renew until 06/10/13 14:21:13
    3. Test Apache HTTP Server Kerberos authentication as follows:

      $ curl --negotiate -u : http://localhost/kerberostest/auth_kerb_page.html

      If it is working correctly, the following result appears:

      <html>
      <body>
          <h1>mod_auth_kerb successfully authenticated!</h1>
      </body>
      </html>

See http://modauthkerb.sourceforge.net/ for more information about mod_auth_kerb.

Appendix A. Apache HTTP Server Reference

A.1. Apache HTTP Server Modules

This section contains expanded definitions of the Apache HTTP Server proxy modules discussed in mod_cluster components.

A.1.1. mod_manager.so

The cluster manager module, mod_manager, 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 in the <VirtualHost> element are as follows:

EnableMCPMReceive
Allows the VirtualHost to receive the mod_cluster Protocol Message (MCPM) from nodes. Add one EnableMCPMReceive directive to the Apache HTTP Server configuration to allow mod_cluster to operate correctly. EnableMCPMReceive must be added in the VirtualHost configuration at the location where advertise is configured.
MaxMCMPMaxMessSize
Defines the maximum size of mod_cluster Management Protocol (MCMP) messages. The default value is calculated from other Max directives. The minimum value is 1024.
AllowDisplay
Toggles the additional display on the mod_cluster-manager main page. The default value is off, which causes only version information to display on the mod_cluster-manager main page.
AllowCmd
Toggles permissions for commands using mod_cluster-manager URL. The default value is on, 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 is off, 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 mod_cluster will use. The default value is 100.
Maxnode
The maximum number of worker nodes mod_cluster will use. The default value is 20.
Maxhost
The maximum number of hosts (aliases) mod_cluster will use. This is also the maximum number of load balancers. The default value is 20.
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 is off.
CheckNonce

When set to on, session identifiers are checked to ensure that they are unique and have not occurred before. The default is on.

Warning

Setting 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>

When accessing the $LOCATION defined in the Location element in your browser, you will see something like the following. (In this case, $LOCATION was also defined as mod_cluster-handler.)

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 when Maxsessionid is 0.

A.1.2. mod_proxy_cluster.so

The Proxy Balancer Module, mod_proxy_cluster, 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

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 the ProxyPass directive.
  • 1: Do not create balancers. When using this value, you must also define the load balancer name in ProxyPass or ProxyPassMatch.
  • 2: Create only the main server. This is the default value for CreateBalancers.
UseAlias

Defines whether to check that the defined Alias corresponds to the ServerName. The following values are valid for UseAlias:

  • 0: Ignore alias information from worker nodes. This is the default value for UseAlias.
  • 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 http://local.com/, then the following ProxyPass directive would convert a local request for http://local.com/requested/file1 into a proxy request for http://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 that gif files should be served locally.

ProxyPassMatch ^(/.*\.gif)$ !

A.1.3. mod_advertise.so

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.

This module must be defined alongside mod_manager in the VirtualHost element. Its identifier in the following example is advertise_module.

LoadModule advertise_module modules/mod_advertise.so

mod_advertise is configurable using the following directives:

ServerAdvertise

Defines how the advertising mechanism is used.

The default value is Off. When set to Off, 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, where ADDRESS must correspond to AdvertiseGroupAddress, and PORT must correspond to AdvertisePort in your worker nodes.

If your worker node is JBoss EAP-based, and the -u switch is used at startup, the default AdvertiseGroupAddress 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 to 23364.

AdvertiseFrequency
The interval (in seconds) between multicast messages advertising the IP address and port. The default value is 10.
AdvertiseSecurityKey
Defines a string used to identify mod_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 is 0.0.0.0:23364.

A.1.4. mod_proxy.so

mod_proxy.so is a standard Apache HTTP Server module. This module lets the server act as proxy for data transferred over AJP (Apache JServe Protocol), FTP, CONNECT (for SSL), and HTTP. This module does not require additional configuration. Its identifier is proxy_module.

Mod_proxy directives such as ProxyIOBufferSize are used to configure mod_cluster.

A.1.5. mod_proxy_ajp.so

mod_proxy_ajp.so is a standard Apache HTTP Server module that provides support for AJP (Apache JServe Protocol) proxying. mod_proxy.so is required to use this module.

A.1.6. mod_cluster_slotmem

mod_cluster_slotmem does not require any configuration directives.

A.2. workers.properties

Apache HTTP Server worker nodes are servlet containers that are mapped to the mod_jk load balancer. The worker nodes are defined in JBCS_HOME/httpd/conf/workers.properties. This file specifies where the different servlet containers are located, and how calls should be load-balanced across them.

The workers.properties file contains two sections:

Global Properties
This section contains directives that apply to all workers.
Worker Properties
This section contains directives that apply to each individual worker.

Each node is defined using the worker properties naming convention. The worker name can only contain lowercase letters, uppercase letters, numbers, and specific special characters (_, /).

The structure of a worker property is worker.WORKER_NAME.DIRECTIVE.

worker
The constant prefix for all worker properties.
WORKER_NAME
The arbitrary name given to the worker. For example: node1, node_01, Node_1.
DIRECTIVE
The specific directive required.

The main directives required to configure worker nodes are described below.

Note

For the full list of worker.properties configuration directives, see the Apache Tomcat Connector - Reference Guide.

worker.properties Global Directives

worker.list

Specifies the list of worker names used by mod_jk. The workers in this list are available to map requests to.

Note

A single node configuration which is not managed by a load balancer must be set to worker.list=WORKER_NAME.

workers.properties Mandatory Directives

type

Specifies the type of worker, which determines the directives applicable to the worker. The default value is ajp13, which is the preferred worker type to select for communication between the web server and Apache HTTP Server.

Other values include lb and status.

For detailed information about AJPv13, see the Apache Tomcat Connector - AJP Protocol Reference.

workers.properties Connection Directives

host

The hostname or IP address of the worker. The worker node must support the ajp13 protocol stack. The default value is localhost.

You can specify the port directive as part of the host directive by appending the port number after the host name or IP address. For example: worker.node1.host=192.168.2.1:8009 or worker.node1.host=node1.example.com:8009.

port
The port number of the remote server instance listening for the defined protocol requests. The default value is 8009, which is the default listen port for AJPv13 workers.
ping_mode

Specifies the conditions under which connections are probed for their current network health.

The probe uses an empty AJPv13 packet for the CPing, and expects a CPong in return, within a specified timeout.

You specify the conditions by using a combination of the directive flags. The flags are not comma-separated. For example, a correct directive flag set is worker.node1.ping_mode=CI.

C (connect)
Specifies the connection is probed once after connecting to the server. You specify the timeout using the connect_timeout directive, otherwise the value for ping_timeout is used.
P (prepost)
Specifies that the connection is probed before sending each request to the server. You specify the timeout using the prepost_timeout directive, otherwise the value for ping_timeout is used.
I (interval)
Specifies that the connection is probed during regular internal maintenance cycles. You specify the idle time between each interval using the connection_ping_interval directive, otherwise the value for ping_timeout is used.
A (all)
The most common setting, which specifies that all directive flags are applied. For information about the \*_timeout advanced directives, see the Apache Tomcat Connector - Reference Guide.
ping_timeout
Specifies the time to wait for CPong answers to a CPing connection probe (see ping_mode). The default value is 10000 (milliseconds).

worker.properties Load Balancing Directives

lbfactor

Specifies the load-balancing factor for an individual worker, and is only specified for a member worker of a load balancer.

This directive defines the relative amount of HTTP request load distributed to the worker compared to other workers in the cluster.

A common example where this directive applies is where you want to differentiate servers with greater processing power than others in the cluster. For example, if you require a worker to take three times the load than other workers, specify worker.WORKER_NAME.lbfactor=3.

balance_workers
Specifies the worker nodes that the load balancer must manage. The directive can be used multiple times for the same load balancer, and consists of a comma-separated list of worker names as specified in the workers.properties file.
sticky_session

Specifies whether requests for workers with SESSION IDs are routed back to the same worker. The default is 0 (false). When set to 1 (true), load balancer persistence is enabled.

For example, if you specify worker.loadbalancer.sticky_session=0, each request is load balanced between each node in the cluster. In other words, different requests for the same session can go to different servers based on server load.

If you specify worker.loadbalancer.sticky_session=1, each session is persisted (locked) to one server until the session is terminated, providing that server is available.

A.3. Multi-Processing Modules (MPMs)

Red Hat JBoss Core Services includes a variety of multi-processing modules (MPMs), allowing for users to customize how the Apache HTTP Server answers incoming requests.

A.3.1. MPM Overview

An overview of the MPMs available per Operating System are outlined below.

A.3.1.1. Unix MPMs

  • prefork - The prefork MPM implements a non-threaded, pre-forking web server. A single control process is responsible for launching child processes, which listen for incoming connections and service them when they arrive. Each request is handled by a single process, ensuring that each request is isolated, and will not affect any other requests.
  • worker - The worker MPM implements a hybrid multi-process, multi-threaded server. Each child process creates a fixed number of server threads, allowing the server to handle a large number of requests with fewer system resources.
  • event - The event MPM is based off the worker MPM, but allows additional requests to be served simultaneously by passing off some processing work to the listener threads, therefore freeing up the worker threads to serve new requests.

A.3.1.2. Windows MPMs

  • winnt - The winnt MPM is the only one available for Windows systems. It uses a single control process, which launches a single process used to create threads for incoming requests.

A.3.2. Switching the MPM

The server selects the MPM based on the LoadModule directive found in JBCS_HOME/httpd/conf.modules.d/00-mpm.conf. By default the prefork MPM is selected, as seen in the following line:

# prefork MPM: Implements a non-threaded, pre-forking web server
# See: http://httpd.apache.org/docs/2.4/mod/prefork.html
LoadModule mpm_prefork_module modules/mod_mpm_prefork.so

To adjust the MPM perform the following steps.

  1. Edit the JBCS_HOME/httpd/conf.modules.d/00-mpm.conf to comment out the LoadModule directive for the prefork MPM. The following XML displays this MPM successfully commented.

    # prefork MPM: Implements a non-threaded, pre-forking web server
    # See: http://httpd.apache.org/docs/2.4/mod/prefork.html
    #LoadModule mpm_prefork_module modules/mod_mpm_prefork.so
  2. In the same file, uncomment the LoadModule directive for the desired MPM. These lines are found immediately below the prefork MPM. For instance, to load the worker MPM the following would be used.

    # worker MPM: Multi-Processing Module implementing a hybrid
    # multi-threaded multi-process web server
    # See: http://httpd.apache.org/docs/2.4/mod/worker.html
    LoadModule mpm_worker_module modules/mod_mpm_worker.so
  3. Confirm the MPM has been configured correctly by running apachectl -V. This command displays the current MPM.

    $ sbin/apachectl -V
    [...]
    Server MPM:     worker
    [...]

Appendix B. Worker Node Reference

B.1. Worker Configuration

Configuration values are sent to proxies under the following conditions:

  • During server startup.
  • When a proxy is detected through the advertise mechanism.
  • During error recovery, when a proxy’s configuration is reset.

Table B.1. Proxy Configuration Values for Tomcat

ValueDefaultDescription

stickySession

true

Specifies whether subsequent requests for a given session should be routed to the same node, if possible.

stickySessionRemove

false

Specifies whether the Apache HTTP Server proxy should remove session stickiness if the balancer is unable to route a request to the node to which it is stuck. This property is ignored if stickySession is false.

stickySessionForce

true

Specifies whether the Apache HTTP Server proxy should return an error if the balancer is unable to route a request to the node to which it is stuck. This property is ignored if stickySession is false.

workerTimeout

-1

Specifies the number of seconds to wait for a worker to become available to handle a request. When all the workers of a balancer are unusable, mod_cluster will retry after a while (workerTimeout/100) to find an usable worker. A value of -1 indicates that the Apache HTTP Server will not wait for a worker to be available and will return an error if no workers are available.

maxAttempts

1

Specifies the number of times the Apache HTTP Server proxy will attempt to send a given request to a worker before aborting. The minimum value is 1: try once before aborting.

flushPackets

false

Specifies whether packet flushing is enabled or disabled.

flushWait

-1

Specifies the time to wait before flushing packets. A value of -1 means wait forever.

ping

10

Time to wait (in seconds) for a pong answer to a ping.

smax

 

Specifies the soft maximum idle connection count. The maximum value is determined by the Apache HTTP Server thread configuration (ThreadsPerChild or 1).

ttl

60

Specifies the time (in seconds) idle connections persist, above the smax threshold.

nodeTimeout

-1

Specifies the time (in seconds) mod_cluster waits for the back-end server response before returning an error. mod_cluster always uses a cping/cpong before forwarding a request. The connectiontimeout value used by mod_cluster is the ping value.

balancer

mycluster

Specifies the name of the load-balancer.

loadBalancingGroup

 

Specifies the load balancing among jvmRoutes within the same load balancing group. A loadBalancingGroup is conceptually equivalent to a mod_jk domain directive.

B.2. mod_cluster Proxy and Proxy Discovery Configuration Attributes

The following tables contain attributes and information about mod_cluster proxy, and proxy discovery configuration attributes.

Table B.2. mod_cluster Proxy Discovery Configuration Attributes

AttributePropertyDefault Value

proxy-list

proxyList

 

proxy-url

proxyURL

 

advertise

advertise

true

advertise-security-key

advertiseSecurityKey

 

excluded-contexts

excludedContexts

 

auto-enable-contexts

autoEnableContexts

true

stop-context-timeout

stopContextTimeout

10 seconds (in seconds)

socket-timeout

nodeTimeout

20 seconds (in milliseconds)

Note

When nodeTimeout is not defined, the ProxyTimeout directive, Proxy, is used. If ProxyTimeout is not defined, the server timeout (Timeout) is used (120 seconds by default in the JBCS httpd.conf). nodeTimeout, ProxyTimeout, and Timeout are set at the socket level.

Table B.3. mod_cluster Proxy Configuration Attributes

AttributePropertyDefault Value

sticky-session

stickySession

true

sticky-session-remove

stickySessionRemove

false

sticky-session-force

stickySessionForce

true

node-timeout

workerTimeout

-1

max-attempts

maxAttempts

1

flush-packets

flushPackets

false

flush-wait

flushWait

-1

ping

ping

10 (seconds)

smax

smax

-1 (uses the default value)

ttl

ttl

-1 (uses the default value)

domain

loadBalancingGroup

 

load-balancing-group

loadBalancingGroup

 

B.3. Load Configuration

The following table contains additional configuration properties that are used when mod_cluster is configured with Tomcat.

Table B.4. Load Configuration for Tomcat

AttributeDefault ValueDescription

loadMetricClass

org.jboss.modcluster.load.metric.impl.BusyConnectorsLoadMetric

The class name of an object that is implementing org.jboss.load.metric.LoadMetric.

loadMetricCapacity

1

The capacity of the load metric defined via the loadMetricClass property.

loadHistory

9

The number of historic load values that must be considered in the load balance factor computation.

loadDecayFactor

2

The factor by which the historic load values decrease in significance.

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