Home > Articles

This chapter is from the book

This chapter is from the book

Implementing a Load-Balancing Mechanism for Your Clustered Servlets and JSPs

As stated earlier in this chapter, you have two options for implementing a load-balancing mechanism for your Presentation tier:

  • Use a WebLogic proxy plug-in.

  • Use a separate load-balancing hardware appliance.

Both options are discussed in detail in the following sections.

Using a WebLogic Proxy Plug-in Load-Balancing Solution

The WebLogic proxy plug-in is an ideal solution if you want to leverage an existing Web tier composed of Netscape, Microsoft, or Apache Web servers to proxy (forward) connection requests to the WebLogic cluster. Alternatively, you can also use WebLogic Server with the HttpClusterServlet as a proxy server.

In a proxy server load-balancing scenario, when an HTTP client requests a servlet or JSP, the proxy plug-in or HttpClusterServlet proxies the request to a managed server in the WebLogic Server cluster. The accessed servlet or JSP maintains data on behalf of a connecting client by using a dedicated HttpSession object, which is created on a per-session basis. When the HTTP response is sent back to a client via the proxy server, the client's browser is instructed to write a cookie that lists the primary and secondary locations of the session's HttpSession object.

TIP

If the client's browser does not support cookies, the managed server can use URL rewriting instead to embed the primary and secondary locations of the HttpSession object into the URLs passed between the client and proxy servers.

The primary location is the address of the managed server that received and processed the initial HTTP connection request. For subsequent HTTP requests, the proxy plug-in or HttpClusterServlet automatically maintains a "sticky" connection between the client and its primary HttpSession object location. The secondary location is the address of a managed server that maintains a replica of the HttpSession object that is used for in-memory session state failover purposes only; this object is discussed later in this chapter.

TIP

The HttpClusterServlet automatically maintains a list of managed servers in a WebLogic cluster, but you will have to configure this information manually and identically for each third-party Web server using the WebLogic proxy plug-in.

The limitation for using a proxy server load-balancing solution is that you are currently constrained to using a round-robin strategy for distributing client requests to the managed servers in a WebLogic cluster.

To showcase the load-balancing capabilities of the WebLogic proxy plug-in, as well as set up a WebLogic environment for subsequent examples in this chapter, the following section discusses how you can easily configure an HttpClusterServlet load-balancing solution.

Configuring the HttpClusterServlet As a Load-Balancing Solution

By default, the HttpClusterServlet is included with every WebLogic Server installation. However, for it to be able to function, the servlet must be deployed as the default application to WebLogic Server that will serve as the proxy server for a domain. Previously in this chapter, you configured the mycluster WebLogic cluster in your WebLogic domain. To demonstrate the load-balancing capabilities of the WebLogic proxy plug-in, you can deploy the HttpClusterServlet as the proxyApp default Web application on the administration server (AdminServer) of your WebLogic domain, which will serve as the proxy server, as illustrated in Figure 25.16.

CAUTION

This configuration is used for demonstration purposes only. In a production environment, you should use a dedicated managed server as a proxy server and ensure the administration server is used only for administration tasks.

Figure 25.16Figure 25.16 Load balancing the mycluster WebLogic cluster using the HttpClusterServlet.

Follow these steps to create and deploy the proxyApp Web application to the administration server of your WebLogic domain:

NOTE

If you use different names for your domain, administration server, and WebLogic cluster, substitute those names where appropriate.

  1. Create a directory named proxyApp in the root of your %BEA_Home%\ objectmind\user_projects directory. Within this directory, create another directory called WEB-INF.

  2. Create a file called web.xml in the WEB-INF directory and open it with any text editor.

  3. Enter the text shown in Listing 25.2, ensuring you modify the names and port numbers of the managed servers you specified when you created your WebLogic cluster.

  4. Listing 25.2 The web.xml File for the proxyApp Application

    <web-app>
      <servlet>
        <servlet-name>HttpClusterServlet</servlet-name>
        <servlet-class>weblogic.servlet.proxy.HttpClusterServlet</servlet-class>
        <init-param>
          <param-name>WebLogicCluster</param-name>
          <param-value>EINSTEIN:7003|EINSTEINt:7005</param-value>
        </init-param>
        <init-param>
          <param-name>DebugConfigInfo</param-name>
          <param-value>ON</param-value>
        </init-param>
      </servlet>
      <servlet-mapping>
        <servlet-name>HttpClusterServlet</servlet-name>
        <url-pattern>/</url-pattern>
      </servlet-mapping>
      <servlet-mapping>
        <servlet-name>HttpClusterServlet</servlet-name>
        <url-pattern>*.jsp</url-pattern>
      </servlet-mapping>
      <servlet-mapping>
        <servlet-name>HttpClusterServlet</servlet-name>
        <url-pattern>*.htm</url-pattern>
      </servlet-mapping>
      <servlet-mapping>
        <servlet-name>HttpClusterServlet</servlet-name>
        <url-pattern>*.html</url-pattern>
      </servlet-mapping>
    </web-app>

    You can also include the following useful parameter, which creates a proxy log file under the default temp directory:

    <init-param>
      <param-name>Debug</param-name>
      <param-value>ALL</param-value>
    </init-param>
  5. Save the file.

  6. Create the proxyApp Web application (WAR file) by executing the following command from within the root of the proxyApp directory:

  7. jar cfv proxyApp.war *.*

    CAUTION

    Ensure that only the WEB-INF directory and web.xml file exist in this directory before you create the proxyApp Web application.

  8. From the left pane of the Administration Console, select Web Applications under the Deployments node and click the Configure a New Web Application link.

  9. At the bottom of the screen, navigate until you find the proxyApp directory you created earlier. Click the proxyApp link and then click the Select link next to proxyApp.war, as shown in Figure 25.17.

  10. Figure 25.17Figure 25.17 Selecting the proxyApp Web application for deployment.

  11. On the Configure Application or Component screen, select your target proxy server (AdminServer) and click Configure and Deploy.

After you deploy the proxyApp Web application, the next task is to specify that it is the default Web application on your proxy server. To do this, follow these steps:

  1. In the left pane of the Administration Console, open the Servers directory and select your proxy server's (AdminServer) node.

  2. Select the Connections, HTTP tab.

  3. Select proxyApp as the Default Web Application and click Apply.

As you can see in Figure 25.18, you can test the HttpClusterServlet by using the following URL in a Web browser, substituting the correct IP address or DNS name and port for your proxy server:

http://EINSTEIN:7001/foo.jsp?__WebLogicBridgeConfig

Figure 25.18Figure 25.18 Testing the functionality of the HttpClusterServlet.

From this point onward, you can access applications deployed on your WebLogic cluster via a single entry point, your proxy server, using the following URL:

http://ip_address_of_proxy_server:port_of_proxy_server/<Application>

Using a Hardware Appliance Load-Balancing Solution

If you require a more sophisticated HTTP connection distribution strategy than just purely a round-robin approach, you should opt to use a hardware load-balancing appliance solution.

In a load-balancing appliance scenario, when a client requests a servlet or JSP directly using an IP address, the load balancer routes the client's connection request to any available managed server in the WebLogic cluster in accordance with a selected load-balancing algorithm supported by the appliance. The managed server that receives the client request serves as the primary location of the client's HttpSession object. The secondary or replica HttpSession object is immediately created on another managed server. As a client initiates subsequent HTTP requests to the WebLogic cluster, the load-balancing appliance uses an identifier in the client-side cookie to ensure these requests are directed to the primary location of the client's HttpSession object.

In its default configuration, WebLogic Server uses client-side cookies to keep track of the primary and secondary locations of the HttpSession object. Hence, to ensure a "sticky" connection between the client and its primary HttpSession object location using cookies, the load-balancing appliance must support a passive or active cookie persistence mechanism, as well as SSL persistence. If cookies are not supported by the client, as in the case of WAP-enabled devices, you must do the following:

  • Enable the managed server's URL rewriting capabilities by setting the URLRewritingEnabled attribute in the weblogic.xml file, under the <session-descriptor> element. The default value for this attribute is true.

  • Configure the load-balancing appliance to extract the location of the primary HttpSession object from inbound URLs.

NOTE

If you decide to use URL rewriting, review BEA's e-docs for coding guidelines on how to programmatically handle URLs in your servlets and JSPs.

InformIT Promotional Mailings & Special Offers

I would like to receive exclusive offers and hear about products from InformIT and its family of brands. I can unsubscribe at any time.

Overview


Pearson Education, Inc., 221 River Street, Hoboken, New Jersey 07030, (Pearson) presents this site to provide information about products and services that can be purchased through this site.

This privacy notice provides an overview of our commitment to privacy and describes how we collect, protect, use and share personal information collected through this site. Please note that other Pearson websites and online products and services have their own separate privacy policies.

Collection and Use of Information


To conduct business and deliver products and services, Pearson collects and uses personal information in several ways in connection with this site, including:

Questions and Inquiries

For inquiries and questions, we collect the inquiry or question, together with name, contact details (email address, phone number and mailing address) and any other additional information voluntarily submitted to us through a Contact Us form or an email. We use this information to address the inquiry and respond to the question.

Online Store

For orders and purchases placed through our online store on this site, we collect order details, name, institution name and address (if applicable), email address, phone number, shipping and billing addresses, credit/debit card information, shipping options and any instructions. We use this information to complete transactions, fulfill orders, communicate with individuals placing orders or visiting the online store, and for related purposes.

Surveys

Pearson may offer opportunities to provide feedback or participate in surveys, including surveys evaluating Pearson products, services or sites. Participation is voluntary. Pearson collects information requested in the survey questions and uses the information to evaluate, support, maintain and improve products, services or sites, develop new products and services, conduct educational research and for other purposes specified in the survey.

Contests and Drawings

Occasionally, we may sponsor a contest or drawing. Participation is optional. Pearson collects name, contact information and other information specified on the entry form for the contest or drawing to conduct the contest or drawing. Pearson may collect additional personal information from the winners of a contest or drawing in order to award the prize and for tax reporting purposes, as required by law.

Newsletters

If you have elected to receive email newsletters or promotional mailings and special offers but want to unsubscribe, simply email information@informit.com.

Service Announcements

On rare occasions it is necessary to send out a strictly service related announcement. For instance, if our service is temporarily suspended for maintenance we might send users an email. Generally, users may not opt-out of these communications, though they can deactivate their account information. However, these communications are not promotional in nature.

Customer Service

We communicate with users on a regular basis to provide requested services and in regard to issues relating to their account we reply via email or phone in accordance with the users' wishes when a user submits their information through our Contact Us form.

Other Collection and Use of Information


Application and System Logs

Pearson automatically collects log data to help ensure the delivery, availability and security of this site. Log data may include technical information about how a user or visitor connected to this site, such as browser type, type of computer/device, operating system, internet service provider and IP address. We use this information for support purposes and to monitor the health of the site, identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents and appropriately scale computing resources.

Web Analytics

Pearson may use third party web trend analytical services, including Google Analytics, to collect visitor information, such as IP addresses, browser types, referring pages, pages visited and time spent on a particular site. While these analytical services collect and report information on an anonymous basis, they may use cookies to gather web trend information. The information gathered may enable Pearson (but not the third party web trend services) to link information with application and system log data. Pearson uses this information for system administration and to identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents, appropriately scale computing resources and otherwise support and deliver this site and its services.

Cookies and Related Technologies

This site uses cookies and similar technologies to personalize content, measure traffic patterns, control security, track use and access of information on this site, and provide interest-based messages and advertising. Users can manage and block the use of cookies through their browser. Disabling or blocking certain cookies may limit the functionality of this site.

Do Not Track

This site currently does not respond to Do Not Track signals.

Security


Pearson uses appropriate physical, administrative and technical security measures to protect personal information from unauthorized access, use and disclosure.

Children


This site is not directed to children under the age of 13.

Marketing


Pearson may send or direct marketing communications to users, provided that

  • Pearson will not use personal information collected or processed as a K-12 school service provider for the purpose of directed or targeted advertising.
  • Such marketing is consistent with applicable law and Pearson's legal obligations.
  • Pearson will not knowingly direct or send marketing communications to an individual who has expressed a preference not to receive marketing.
  • Where required by applicable law, express or implied consent to marketing exists and has not been withdrawn.

Pearson may provide personal information to a third party service provider on a restricted basis to provide marketing solely on behalf of Pearson or an affiliate or customer for whom Pearson is a service provider. Marketing preferences may be changed at any time.

Correcting/Updating Personal Information


If a user's personally identifiable information changes (such as your postal address or email address), we provide a way to correct or update that user's personal data provided to us. This can be done on the Account page. If a user no longer desires our service and desires to delete his or her account, please contact us at customer-service@informit.com and we will process the deletion of a user's account.

Choice/Opt-out


Users can always make an informed choice as to whether they should proceed with certain services offered by InformIT. If you choose to remove yourself from our mailing list(s) simply visit the following page and uncheck any communication you no longer want to receive: www.informit.com/u.aspx.

Sale of Personal Information


Pearson does not rent or sell personal information in exchange for any payment of money.

While Pearson does not sell personal information, as defined in Nevada law, Nevada residents may email a request for no sale of their personal information to NevadaDesignatedRequest@pearson.com.

Supplemental Privacy Statement for California Residents


California residents should read our Supplemental privacy statement for California residents in conjunction with this Privacy Notice. The Supplemental privacy statement for California residents explains Pearson's commitment to comply with California law and applies to personal information of California residents collected in connection with this site and the Services.

Sharing and Disclosure


Pearson may disclose personal information, as follows:

  • As required by law.
  • With the consent of the individual (or their parent, if the individual is a minor)
  • In response to a subpoena, court order or legal process, to the extent permitted or required by law
  • To protect the security and safety of individuals, data, assets and systems, consistent with applicable law
  • In connection the sale, joint venture or other transfer of some or all of its company or assets, subject to the provisions of this Privacy Notice
  • To investigate or address actual or suspected fraud or other illegal activities
  • To exercise its legal rights, including enforcement of the Terms of Use for this site or another contract
  • To affiliated Pearson companies and other companies and organizations who perform work for Pearson and are obligated to protect the privacy of personal information consistent with this Privacy Notice
  • To a school, organization, company or government agency, where Pearson collects or processes the personal information in a school setting or on behalf of such organization, company or government agency.

Links


This web site contains links to other sites. Please be aware that we are not responsible for the privacy practices of such other sites. We encourage our users to be aware when they leave our site and to read the privacy statements of each and every web site that collects Personal Information. This privacy statement applies solely to information collected by this web site.

Requests and Contact


Please contact us about this Privacy Notice or if you have any requests or questions relating to the privacy of your personal information.

Changes to this Privacy Notice


We may revise this Privacy Notice through an updated posting. We will identify the effective date of the revision in the posting. Often, updates are made to provide greater clarity or to comply with changes in regulatory requirements. If the updates involve material changes to the collection, protection, use or disclosure of Personal Information, Pearson will provide notice of the change through a conspicuous notice on this site or other appropriate way. Continued use of the site after the effective date of a posted revision evidences acceptance. Please contact us if you have questions or concerns about the Privacy Notice or any objection to any revisions.

Last Update: November 17, 2020