Apache HTTP Server Connectors and Load Balancing Guide

Red Hat JBoss Core Services 2.4.37

For Use with Red Hat JBoss Core Services 2.4.37

Red Hat Customer Content Services

Abstract

Install and configure load-balancing solutions that use the `mod_cluster` and `mod_jk` connector modules along with other modules that Red Hat JBoss Core Services provides.

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Chapter 1. HTTP connector modules

Red Hat JBoss Core Services includes two different HTTP connector modules that you can use to load-balance HTTP requests to a set of back-end servlet containers:

  • The Apache Tomcat connector (mod_jk) supports the load balancing of HTTP requests to a set of servlet containers, while maintaining sticky sessions and communicating over the Apache JServ Protocol (AJP).
  • The JBoss HTTP connector (mod_cluster) is a more advanced load balancer than mod_jk. The mod_cluster module 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.

The Apache HTTP Server Connectors and Load Balancing Guide describes how to install and configure the mod_proxy and mod_cluster connectors. This guide also provides information about Online Certificate Status Protocol (OCSP) and includes 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 an archive 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.

Important

Red Hat Enterprise Linux 6 is no longer supported and subsequently was removed from the documentation.

Chapter 2. Load balancing with the Apache Tomcat connector (mod_jk)

The Apache Tomcat Connector, mod_jk, is a plug-in that allows the Apache HTTP Server to forward web requests to a back-end servlet container. The mod_jk module also allows the Apache HTTP Server to load-balance requests to a set of servlet containers, while maintaining sticky sessions.

2.1. Mod_jk installation

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

You can follow the procedures in the Red Hat JBoss Core Services Apache HTTP Server Installation Guide to download and install the Apache HTTP Server for your operating system.

2.2. Apache HTTP Server load-balancing configuration when using mod_jk

You can configure the Apache HTTP Server to use mod_jk to load-balance requests to a set of servlet containers. This setup includes the configuration of back-end worker nodes.

Red Hat JBoss Core Services provides example configuration files for mod_jk in the JBCS_HOME/httpd/conf.d/ directory. These example configuration files are named mod_jk.conf.sample, workers.properties.sample, and uriworkermap.properties.sample. To use these examples instead of creating your own configuration files, you can remove the .sample extension, and modify the file content as needed.

Note

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

When you use the Load Balancer Configuration tool for Apache HTTP Server 2.4.37, ensure that you select 2.4.x as the Apache version, and select Tomcat as the back-end configuration.

When the Apache HTTP Server (httpd) is installed on Red Hat Enterprise Linux 8, the base operating system modules are located in the /usr/lib64/httpd/modules directory. The Red Hat JBoss Core Services modules are currently located in the /opt/rh/jbcs/root/usr/lib64/httpd/modules directory.

The Red Hat JBoss Core Services modules include mod_jk, mod_cluster, mod_rt, and mod_bmx. These modules follow all Red Hat JBoss Core Services rules for naming, directories, and prefixes. If you want to use these modules, create or modify a configuration file to add the LoadModule command. For example:

LoadModule jk_module /opt/rh/jbcs/root/usr/lib64/httpd/modules/mod_jk.so

Alternatively, you can include the directory of the installed Red Hat JBoss Core Services modules in the JBCS_HOME/httpd/conf.d directory.

Important

Consider the following differences between the httpd implementations that are provided by JBoss Core Services and Red Hat Enterprise Linux:

  • You can install JBoss Core Services httpd from an archive file or RPM package.
  • You can also install JBoss Core Services httpd in a Windows Server environment.
  • JBoss Core Services httpd does not provide or support the mod_php module. Red Hat Enterprise Linux httpd supports the mod_php module.
  • JBoss Core Services httpd provides the mod_jk and mod_cluster load balancer modules. Red Hat Enterprise Linux httpd does not provide the mod_jk and mod_cluster modules.

The use case for JBoss Core Services httpd is to connect to the back end with a proxy. You can use mod_jk, mod_proxy_cluster, or mod_proxy as a proxy. There is no difference between these modules in the httpd implementations that are provided by Red Hat JBoss Core Services and Red Hat Enterprise Linux.

Note

Since the 2.4.37 Service Pack 10 release, Red Hat JBoss Core Services does not support the tunneling of non-upgraded connections to a back-end WebSockets server. This means that when you are configuring the ProxyPass directive for the mod_proxy_wstunnel module, you must ensure that the upgrade parameter is not set to NONE. For more information about mod_proxy_wstunnel, see the Apache documentation.

2.3. Configuring the Apache HTTP Server to load mod_jk

You can configure the Apache HTTP Server to load mod_jk, by specifying configuration settings in the mod_jk.conf file.

You can also perform the following optional configuration steps:

  • In addition to the JkMount directive, you can use the JkMountFile directive to specify the configuration file for a mount point. The configuration file contains multiple URL mappings for Tomcat forwarding.
  • You can configure the Apache HTTP Server that is functioning as the load balancer to log details of each worker node that handles a request. This can be useful if you need to troubleshoot your load balancer.

Procedure

  1. Go to the JBCS_HOME/httpd/conf.d directory.
  2. Create a new file named mod_jk.conf and enter the following configuration details:

    # 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

    Ensure that the LoadModule directive references the mod_jk native binary that you have installed.

    Note

    The JkMount directive specifies the URLs that the Apache HTTP Server can forward to the mod_jk module. Based on the configuration for the JkMount directive, mod_jk forwards the received URL to the correct servlet containers.

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

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

  3. Optional: To use the JkMountFile directive to specify the configuration file for a mount point, perform the following steps:

    1. Go to the JBCS_HOME/httpd/conf.d/ directory.
    2. Create a file named uriworkermap.properties.
    3. Specify the URL that you want to forward and the worker name.

      For example:

      # Simple worker configuration file
      
      # Mount the Servlet context to the ajp13 worker
      /application=loadbalancer
      /application/*=loadbalancer
      Note

      The required syntax is in the format: /URL=WORKER_NAME

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

    4. In the JBCS_HOME/httpd/conf.d/mod_jk.conf file, enter 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
  4. Optional: To enable Apache HTTP Server logging, perform either of the following steps:

    • Include %w in your JkRequestLogFormat directive, as shown in the preceding step about mod_jk.conf settings.
    • Log the name of the mod_jk worker that you want to use, by including %{JK_WORKER_NAME}n in your Apache HTTP Server LogFormat(s).

2.4. Configuring worker nodes in mod_jk

You can configure multiple worker nodes to handle the requests that the Apache HTTP Server forwards to the servlet containers.

The example in this procedure shows how to define two mod_jk worker nodes in a weighted round-robin configuration that uses sticky sessions between two servlet containers.

Prerequisites

Procedure

  1. Go to the JBCS_HOME/httpd/conf.d/ directory.
  2. Create a file named workers.properties.
  3. Enter the following configuration details:

    # 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
    worker.node1.secret=<YourSecret>
    
    # 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
    worker.node1.secret=<YourSecret>
    
    # 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
    Note

    In the preceding example, ensure that you replace host, port, and secret settings with values that are relevant for your environment.

    Important

    The secret property is required when using the Tomcat AJP Connector. You can specify the secret property for a worker node or a load balancer in the workers.properties file. For example:

    worker.<WORKER_NAME>.secret=<YOUR_AJP_SECRET>

    In the preceding example, replace <WORKER_NAME> and <YOUR_AJP_SECRET> with values that are relevant for your environment.

2.5. Configuring Tomcat to work with mod_jk

Tomcat is configured to receive Apache JServ Protocol (AJP) traffic from mod_jk by default. However, before you can use a worker node with mod_jk, you must perform the following additional configuration steps:

  • Configure the AJP connector. The AJP connector is not configured by default.
  • Configure a unique value for the jvmRoute attribute in the Engine of each worker node.
  • Specify the secret property for a worker node or a load balancer. The secret property is required when you use the Tomcat AJP connector.

Procedure

  1. To configure the AJP connector, perform the following steps:

    1. Open the JBCS_HOME/tomcat<VERSION>/conf/server.xml file.
    2. In the server.xml file, enter the following line:

      <Connector port="8009" protocol="AJP/1.3" redirectPort="8443" />
  2. To configure a unique value for the jvmRoute attribute in the Engine of each worker node, enter the following details:

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

    Ensure that the jvmRoute attribute value matches the worker name that is specified in the workers.properties file.

  3. To specify the secret property for a worker node or a load balancer, perform the following steps:

    1. Open the JBCS_HOME/httpd/conf.d/workers.properties file.
    2. In the workers.properties file, ensure that the secret property is specified in the following format:

      worker.<WORKER_NAME>.secret=<YOUR_AJP_SECRET>`
      Note

      Ensure that you replace <WORKER_NAME> and <YOUR_AJP_SECRET> with values that are relevant for your environment.

      Note

      If you set a secret on a load balancer by using the ProxyPass directive, all of its members inherit this secret. For example:

      <Proxy balancer://mycluster>`
          BalancerMember ajp://node1:8009 route=node1 secret=YOUR_AJP_SECRET
          BalancerMember ajp://node2:8009 route=node2 secret=YOUR_AJP_SECRET
      </Proxy>
      ProxyPass /example/ balancer://mycluster/example/ stickysession=JSESSIONID|jsessionid

Chapter 3. Load balancing with the JBoss HTTP connector (mod_cluster)

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

3.1. JBoss HTTP connector (mod_cluster)

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

Key features of mod_cluster

The mod_cluster connector has several advantages over the mod_jk connector:

  • When the mod_cluster module is enabled, the mod_cluster Management Protocol (MCMP) is an additional connection between the Tomcat servers and the Apache HTTP Server. The Tomcat servers use MCMP to transmit server-side load figures and lifecycle events back to the Apache HTTP Server, by using 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 the need for manual configuration.
  • Tomcat servers perform the load calculations rather than rely on the Apache HTTP Server. This makes load-balancing metrics more accurate than other connectors.
  • The mod_cluster connector provides fine-grained application lifecycle control. Each Tomcat server forwards web application context lifecycle events to the Apache HTTP Server. These lifecycle events include informing the Apache HTTP Server to start or stop routing requests for a specific context. This prevents end users from seeing HTTP errors because of unavailable resources.
  • You can use Apache JServ Protocol (AJP), Hypertext Transfer Protocol (HTTP), or Hypertext Transfer Protocol Secure (HTTPS) transports with mod_cluster.

Mod_cluster components

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

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.

Additional resources

3.2. Mod_cluster character limits

The mod_cluster module 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 you define proxy server and worker node properties, ensure that you adhere to the following character limits:

PropertyMaximum character limitDescription

Alias length

100 characters

Alias corresponds to the network name of the respective virtual host; the name is defined in the Host element.

Context length

40 characters

For example, if myapp.war is deployed in /myapp , /myapp is included in the context.

Balancer name length

40 characters

This is the balancer property in mbean.

JVMRoute string length

80 characters

JVMRoute in the <Engine> element.

Domain name length

20 characters

This is the domain property in mbean.

Hostname length for a node

64 characters

This is hostname address in the <Connector> element.

Port length for a node

7 characters

This is the port property in the <Connector> element. For example, 8009 is 4 characters.

Scheme length for a node

6 characters

This is the protocol of the connector. Possible values are http, https, and ajp.

Cookie name length

30 characters

This is the header cookie name for the session ID. The default value is JSESSIONID based on the org.apache.catalina.Globals.SESSION_COOKIE_NAME property.

Path name length

30 characters

This is the parameter name for the session ID. The default value is JSESSIONID based on the org.apache.catalina.Globals.SESSION_PARAMETER_NAME property.

Session ID length

120 characters

A session ID is in the following type of format: BE81FAA969BF64C8EC2B6600457EAAAA.node01

3.3. Mod_cluster installation

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

You can follow the procedures in the Red Hat JBoss Core Services Apache HTTP Server Installation Guide to download and install the Apache HTTP Server for your operating system.

3.4. Apache HTTP Server load-balancing configuration when using mod_cluster

In Apache HTTP Server 2.1 and higher, mod_cluster is configured correctly for Apache HTTP Server by default. For more information about setting a custom configuration, see Configuring a basic proxy server.

Note

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

When you use the Load Balancer Configuration tool for Apache HTTP Server 2.4.37, ensure that you select 2.4.x as the Apache version, and select Tomcat as the back-end configuration.

When the Apache HTTP Server (httpd) is installed on Red Hat Enterprise Linux 8, the base operating system modules are located in the /usr/lib64/httpd/modules directory. The Red Hat JBoss Core Services modules are currently located in the /opt/rh/jbcs/root/usr/lib64/httpd/modules directory.

The Red Hat JBoss Core Services modules include mod_jk, mod_cluster, mod_rt, and mod_bmx. These modules follow all Red Hat JBoss Core Services rules for naming, directories, and prefixes. If you want to use these modules, create or modify a configuration file to add the LoadModule command. For example:

LoadModule jk_module /opt/rh/jbcs/root/usr/lib64/httpd/modules/mod_jk.so

Alternatively, you can include the directory of the installed Red Hat JBoss Core Services modules in the JBCS_HOME/httpd/conf.d directory.

Note
  • When you want to use the mod_proxy_cluster module, you must enable the mod_proxy module and disable the mod_proxy_balancer module.
  • If you want mod_proxy_cluster to use the Apache JServ Protocol (AJP), you must enable the proxy_ajp_module.
  • Use AJPSecret your_secret to provide the secret for the AJP backend. If your_secret does not correspond to the value configured in the back end, the back end sends a 503 error response for any request that is sent through the proxy.
Note

Since the 2.4.37 Service Pack 10 release, Red Hat JBoss Core Services does not support the tunneling of non-upgraded connections to a backend websockets server. This means that when you are configuring the ProxyPass directive for the mod_proxy_wstunnel module, you must ensure that the upgrade parameter is not set to NONE. For more information about mod_proxy_wstunnel, see the Apache documentation.

3.5. Configuring a basic proxy server

You can configure the Apache HTTP Server to function as a proxy server that forwards requests and responses between web clients and back-end web servers. You must configure a proxy server listener to receive connection requests and responses from the back-end worker nodes. When you want to configure a load-balancing proxy server that uses mod_cluster, you must also configure a virtual host for the management channel.

Prerequisites

Procedure

  1. Open the mod_cluster configuration file.

    Note

    The mod_cluster configuration file is typically located in the JBCS_HOME/httpd/conf.d/mod_cluster.conf directory.

  2. To create a Listen directive for the proxy server, enter the following line in the mod_cluster.conf file:

    Listen IP_ADDRESS:PORT_NUMBER
    Note

    In the preceding example, replace IP_ADDRESS with the address of the server network interface that the proxy server uses to communicate with the worker nodes, and replace PORT_NUMBER with the port that the proxy server listens on.

    Ensure that the port is open for incoming TCP connections.

  3. To create a virtual host, enter the following details in the mod_cluster.conf file:

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

    In the preceding example, replace IP_ADDRESS and PORT_NUMBER with the address of the server network interface and port number that you have specified for the Listen directive.

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

For more information about configuring mod_jk and starting the Apache HTTP Server service, see the Red Hat JBoss Core Services Apache HTTP Server Installation Guide.

3.5.1. Disabling server advertisement

The proxy server uses UDP multicast to advertise itself. The AdvertiseFrequency directive instructs the server to send server advertisement messages every 10 seconds by default. Server advertisement messages contain the IP_ADDRESS and PORT_NUMBER that you specify in the VirtualHost definition. Worker nodes that are configured to respond to server advertisements use this information to register themselves with the proxy server. If you want to prevent worker nodes from registering with the proxy server, you can optionally disable server advertisement.

Note

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. Server advertisement requires only minimal configuration on the worker nodes.

Prerequisites

Procedure

  1. Open the mod_cluster configuration file.

    Note

    The mod_cluster configuration file is typically located in the JBCS_HOME/httpd/conf.d/mod_cluster.conf directory.

  2. Add the following directive to the VirtualHost definition:

    ServerAdvertise Off
    Note

    If server advertisements are disabled, or UDP multicast is not available on the network between the proxy server and the worker nodes, you can configure worker nodes with a static list of proxy servers. In either case, you do not need to configure the proxy server with a list of worker nodes.

3.5.2. Logging worker node details

When you configure a load-balancing proxy server that uses mod_cluster, you can optionally configure the Apache HTTP Server to log details of each worker node that handles a request. Logging worker node details can be useful if you need to troubleshoot your load balancer.

Prerequisites

Procedure

  1. Open the mod_cluster configuration file.

    Note

    The mod_cluster configuration file is typically located in the JBCS_HOME/httpd/conf.d/mod_cluster.conf directory.

  2. Add the following details 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.

3.6. Configuring a Tomcat worker node in mod_cluster

When you use mod_cluster, you can configure a Tomcat worker node as an Apache HTTP Server Tomcat service that operates in non-clustered mode only. In this situation, only one load metric can be used at a time when calculating the load-balance factor.

Note

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

Procedure

  1. To add a listener to Tomcat, add the following Listener element beneath the other Listener elements in the JWS_HOME/tomcat<VERSION>/conf/server.xml file:

    <Listener className="org.jboss.modcluster.container.catalina.standalone.ModClusterListener" advertise="true" stickySession="true" stickySessionForce="false" stickySessionRemove="true" />
  2. To give the worker node a unique identity, edit the JWS_HOME/tomcat<VERSION>/conf/server.xml file, to add the jvmRoute attribute and value to the Engine element:

    <Engine name="Catalina" defaultHost="localhost" jvmRoute="worker01">
  3. To configure STATUS MCMP message frequency, modify the org.jboss.modcluster.container.catalina.status-frequency Java system property.

    For example:

    -Dorg.jboss.modcluster.container.catalina.status-frequency=6
    Note

    Tomcat worker nodes periodically send status messages that contain 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 that are specified in seconds multiplied by 10. For example, setting the property to 1 means 10 seconds. In the preceding example, the property is set to 6, which means 60 seconds.

  4. Optional: To configure the firewall for proxy server advertisements, complete either of the following steps to open port 23364 for UDP connections on the worker node’s firewall:

    • 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"'
      Note

      When a proxy server uses mod_cluster, the proxy server can use UDP multicast to advertise itself. Most operating system firewalls block the server advertisement feature by default. To enable server advertisement and receive these multicast messages, you can open port 23364 for UDP connections on the worker node’s firewall, as shown in the preceding examples.

Important

Red Hat Enterprise Linux 6 is no longer supported and subsequently was removed from the documentation.

3.7. Configuring a worker node to operate with a static list of proxy servers

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

Procedure

  1. Open the JWS_HOME/tomcat<VERSION>/conf/server.xml file.
  2. To define a mod_cluster listener and disable dynamic proxy discovery, add or change the Listener element for ModClusterListener.

    For example:

    <Listener className="org.jboss.modcluster.container.catalina.standalone.ModClusterListener" advertise="false" stickySession="true" stickySessionForce="false" stickySessionRemove="true"/>
    Note

    Ensure that you set the advertise property to false.

  3. To create a static proxy server list, update the proxyList property by adding a comma-separated list of proxies in the following format: IP_ADDRESS:PORT,IP_ADDRESS:PORT

    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. Securing connections by using OCSP

Online Certificate Status Protocol (OCSP) is a technology that 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.

4.1. Online Certificate Status Protocol

When a web browser and a web server communicate over a secured connection, the server presents a set of credentials in the form of a certificate. The browser then validates the certificate and sends a request for certificate status information. The server responds with a certificate status of current, expired, or unknown.

The certificate contains the following types of information:

  • Syntax for communication
  • Control information such as start time, end time, and address information to access an Online Certificate Status Protocol (OCSP) responder.

The web server uses an OCSP responder to check the certificate status. You can configure the web server to use the OCSP responder that is listed in the certificate or another OCSP responder. 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 Certificate Revocation List (CRL) method.

4.2. Configuring the Apache HTTP Server for SSL connections

You can configure the Apache HTTP Server to support SSL connections, by installing the mod_ssl package and specifying configuration settings in the ssl.conf file.

Prerequisites

  • You have generated an SSL certificate and private key.
  • You know the location of the SSL certificate and private key file.
  • You have obtained the Common Name (CN) that is associated with the SSL certificate.

Procedure

  1. To install mod_ssl, enter the following command:

    # yum install jbcs-httpd24-mod_ssl
  2. To specify SSL configuration settings:

    1. Open the JBCS_HOME/httpd/conf.d/ssl.conf file.
    2. Enter details for the ServerName, SSLCertificateFile, and SSLCertificateKeyFile.

      For example:

      <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
      Note
      • The ServerName must match the Common Name (CN) that is associated with the SSL certificate. If the ServerName does not match the CN, client browsers display domain name mismatch errors.
      • The SSLCertificateFile specifies the path to the SSL certificate file.
      • The SSLCertificateKeyFile specifies the path to the private key file that is associated with the SSL certificate.
  3. Verify that the Listen directive matches the hostname or IP address for the httpd service for your deployment.
  4. To restart the Apache HTTP Server, enter the following command:

    # service jbcs-httpd24-httpd restart

4.3. Using OCSP with the Apache HTTP Server

You can use the Online Certificate Status Protocol (OCSP) for secure connections with the Apache HTTP Server.

Procedure

  1. Configure a certificate authority.

    Note

    Ensure that your CA can issue OCSP certificates. The CA 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

    In the preceding example, replace HOST and PORT with the details of the OCSP responder that you will configure.

  2. Configure an OCSP responder.

4.4. Configuring the Apache HTTP Server to validate OCSP certificates

You can configure the Apache HTTP Server to validate OCSP certificates, by defining OCSP settings in the ssl_conf file.

Procedure

  1. Open the JBCS_HOME/httpd/conf.d/ssl.conf file.
  2. Specify the appropriate OCSP configuration details for your deployment.

    For example:

    # Require valid client certificates (mutual auth)
    SSLVerifyClient require
    SSLVerifyDepth  3
    # Enable OCSP
    SSLOCSPEnable on
    SSLOCSPDefaultResponder http://<HOST>:<PORT>
    SSLOCSPOverrideResponder on
    Note

    The preceding example shows how to enable OCSP validation of client certificates. In the preceding example, replace <HOST> and <PORT> with the IP address and port of the default OCSP Responder.

4.5. Verifying the OCSP configuration for the Apache HTTP Server

You can use the OpenSSL command-line tool to verify the OCSP configuration for the Apache HTTP Server.

Procedure

  • On the command line, enter the openssl command in the following format:

    # openssl ocsp -issuer cacert.crt -cert client.cert -url http://HOST:PORT -CA ocsp_ca.cert -VAfile ocsp.cert

    In the preceding command, ensure that you specify the following details:

    • Use the -issuer option to specify the CA certificate.
    • Use the -cert option to specify the client certificate that you want to verify.
    • Use the -url option to specify the HTTP server validating Certificate (OCSP).
    • Use the -CA option to specify the is the CA certificate for verifying the Apache HTTP Server server certificate.
    • Use the -VAfile option to specify the OCSP responder certificate.

Chapter 5. Configuration example for load-balancing with mod_cluster

You can configure JBoss Core Services to use the mod_cluster connector for load-balancing in a Red Hat Enterprise Linux system.

When you want to configure a load-balancing solution that uses mod_cluster, you must perform the following tasks:

5.1. Setting up JBoss Core Services as a proxy server

When you configure JBoss Core Services to use mod_cluster, you must set up JBoss Core Services as a proxy server by specifying configuration details in the mod_cluster.conf file.

Procedure

  1. Go to the JBCS_HOME/httpd/conf.d/ directory.
  2. Create a file named mod_cluster.conf.
  3. Enter the following configuration details:

    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>
    Note

    The preceding example shows how to set up JBoss Core Services as a proxy server that is listening on localhost.

5.2. Configuring a Tomcat worker node

When you configure JBoss Core Services to use mod_cluster, you must configure a Tomcat worker node by adding a Listener element to the server.xml file.

Procedure

  1. Open the JWS_HOME/tomcat<VERSION>/conf/server.xml file.
  2. Add the following Listener element:

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

5.3. Defining iptables firewall rules example

When you configure JBoss Core Services to use mod_cluster, you must define firewall rules by using iptables.

Prerequisites

Procedure

  • Use iptables to define a set of firewall rules.

    For example:

    /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
    Note

    The preceding example shows to define firewall rules for a cluster node on the 192.168.1.0/24 subnet.

Chapter 6. Configuration example for Kerberos authentication with mod_auth_kerb

You can configure Kerberos authentication with the JBoss Core Services Apache HTTP Server and the mod_auth_kerb module on Red Hat Enterprise Linux.

When you want to configure Kerberos authentication, you must perform the following tasks:

6.1. Prerequisites

  • You have installed the curl command-line utility with Generic Security Services (GSS)-negotiated support.
  • You have configured and run a Kerberos or LDAP server, such as ApacheDS, on the same host as JBoss Core Services.
  • If you are using an LDAP server, you have created LDAP users called krbtgt, ldap, HTTP, and a test LDAP user called hnelson.

    • To create the krbtgt user, enter the following details:

      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
    • To create the ldap user, enter the following details:

      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
    • To create the HTTP user, enter the following details:

      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
    • To create the test user, hnelson, enter the following details:

      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

6.2. Configuring the Kerberos client

When you configure Kerberos authentication, you must configure the Kerberos client by performing the following steps:

  1. Specify configuration settings in the krb5.conf file.
  2. Create a key tab in the JBCS_HOME/httpd/conf file.
  3. Assign permissions to the key tab.
  4. Ensure that localhost is included in the /etc/hosts file.

Prerequisites

Procedure

  1. To specify configuration settings in the krb5.conf file:

    1. Go to the /etc directory.
    2. Create a file named krb5.conf.
    3. Enter the following configuration details:

      [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. To create a key tab:

    1. Open the JBCS_HOME/httpd/conf file.
    2. Enter the following details:

      # 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. You must substitute the full path for the JBCS_HOME variable.

  3. To apply the correct group and permissions to the key tab, enter the following commands as the root user:

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

    127.0.0.1 localhost

6.3. Configuring mod_auth_kerb

When you configure Kerberos authentication, you must configure mod_auth_kerb by specifying settings in the auth_kerb.conf file.

Prerequisites

Procedure

  1. Go to the JBCS_HOME/httpd/conf.d/ directory.
  2. Create a file named auth_kerb.conf.
  3. Enter the following configuration details:

    #
    # 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. In the preceding example, ensure that you substitute the full path for the JBCS_HOME variable.

6.4. Testing the Kerberos authentication

When you configure Kerberos authentication, you can use a test page to test the Kerberos authentication.

Prerequisites

Procedure

  1. To create a test page, perform the following steps:

    1. Go to the JBCS_HOME/httpd/www/html/kerberostest directory.
    2. Create a test page named auth_kerb_page.html.
    3. Enter the following details:

      <html>
      <body>
          <h1>mod_auth_kerb successfully authenticated!</h1>
      </body>
      </html>
  2. Optional: In the JBCS_HOME/httpd/conf/httpd.conf file, set the log level to debugging.
  3. Start the Apache HTTP Server. For more information, see the Red Hat JBoss Core Services Apache HTTP Server Installation Guide.
  4. To initiate Kerberos authentication for the test user, hnelson, enter the following command:

    $ kinit hnelson
  5. To view the details for the test user, hnelson, enter the following command:

    $ klist

    The klist command produces the following type of output:

    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

Verification

  • To test Kerberos authentication, enter the following command:

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

    If Kerberos authentication is working correctly, the curl command produces the following output:

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

6.5. Additional resources (or Next steps)

Appendix A. Apache HTTP Server proxy modules

This section contains expanded definitions of the Apache HTTP Server proxy modules that mod_cluster includes.

A.1. Mod_manager module and directives

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 for mod_manager

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.

Note

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.2. Mod_proxy_cluster module and directives

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

Configurable directives for mod_proxy_cluster

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 such as http://local.com/, the following ProxyPass directive converts 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.3. Mod_advertise module and directives

The Proxy Advertisement Module, mod_advertise, 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

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 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 that is 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.4. Mod_proxy module and directives

The mod_proxy module is a standard Apache HTTP Server module that enables the server to act as a proxy for data transferred over the AJP (Apache JServe Protocol), FTP, CONNECT (for SSL), and HTTP protocols. The mod_proxy module does not require additional configuration. The identifier for the mod_proxy module is proxy_module.

The configurable directives for mod_proxy, such as ProxyIOBufferSize, are used to configure the mod_cluster module.

A.5. Mod_proxy_ajp module and directives

The mod_proxy_ajp module is a standard Apache HTTP Server module that provides support for AJP (Apache JServe Protocol) proxying. The mod_proxy module is also required if you want to use mod_proxy_ajp. Additionally, the secret property is required when using the Tomcat AJP Connector. The secret property can be added to the ProxyPass settings using the following command:

ProxyPass /example/ ajp://localhost:8009/example/ secret=YOUR_AJP_SECRET

Note

If you set a secret on a load balancer, all of its members inherit this secret.

A.6. Mod_cluster_slotmem module and directives

The mod_cluster_slotmem 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.

Appendix B. Workers.properties file

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.

B.1. Workers.properties overview

The workers.properties file contains a global properties section and a worker properties section.

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.

B.2. Workers.properties directives

The workers.properties file directives are divided into global, mandatory, connection, and load-balancing classifications.

Global directives for workers.properties

worker.list

Specifies the list of worker names that mod_jk uses. 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.

Mandatory directives for workers.properties

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.

Connection directives for workers.properties

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).

Load balancing directives for workers.properties

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.

Appendix C. Multi-processing modules (MPMs)

Red Hat JBoss Core Services includes a variety of multi-processing modules (MPMs). You can use these MPMs to customize how the Apache HTTP Server responds to incoming requests.

C.1. MPMs overview

Multi-processing modules (MPMs) are available for both Red Hat Enterprise Linux and Microsoft Windows.

MPMs for Red Hat Enterprise Linux

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.

MPMs for Microsoft Windows

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.

C.2. Switching the MPM

The server selects the MPM based on the LoadModule directives in the JBCS_HOME/httpd/conf.modules.d/00-mpm.conf file. You can select a specific MPM by removing the comment character (#) from the LoadModule directive for that MPM in the 00-mpm.conf file.

By default, the prefork MPM is selected. For example:

# 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

Procedure

  1. Edit the JBCS_HOME/httpd/conf.modules.d/00-mpm.conf to add a comment (#) character to the LoadModule directive for the prefork MPM. For example:

    # 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 00-mpm.conf file, remove the comment (#) character from the LoadModule directive for the MPM that you want to switch to. These lines are located immediately below the prefork MPM.

    For example, to load the worker MPM, remove the comment (#) character from the LoadModule directive for the worker MPM:

    # 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. To verify the MPM is configured correctly, enter the following command:

    $ sbin/apachectl -V

    This command displays the current MPM. For example:

    Server MPM:     worker

Appendix D. Worker node 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 D.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.

Appendix E. 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 E.1. Proxy discovery configuration attributes for mod_cluster

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 E.2. Proxy configuration attributes for mod_cluster

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

 

Appendix F. Load configuration for Tomcat

You can configure the following additional properties for load metrics when you want to use mod_cluster with Apache Tomcat.

Table F.1. 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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