Home > Articles

This chapter is from the book

This chapter is from the book

BEA WebLogic Platform 7BEA WebLogic Platform 7

Learn More Buy

This chapter is from the book

This chapter is from the book

BEA WebLogic Platform 7BEA WebLogic Platform 7

Learn More Buy

Designing the Architecture of a WebLogic Cluster

To implement a WebLogic cluster that meets the high-availability and scalability requirements of your J2EE application, you must understand the elements that constitute a WebLogic clustering environment as well as the benefits of one type of clustering design over another. The following section addresses these two topics and brings clarity to how you can architecturally design your WebLogic cluster.

Understanding a Typical Clustering Environment

If you are new to the concept of clustering, it is imperative for you to understand what constitutes a typical WebLogic clustering environment before you even begin to design an architecture for your WebLogic cluster.

As illustrated in Figure 25.4, a typical WebLogic cluster environment can consist of the following logical software tiers and services, which do not necessarily imply a division in hardware in the overall clustering architecture.

Figure 25.4Figure 25.4 The typical software tiers and services that can constitute a WebLogic cluster environment.

The Load Balancer

A load balancer is a software or hardware mechanism that can distribute client connection requests to the servers in a WebLogic cluster. The objective of a load balancer is to ensure all clustered servers service incoming requests in the most optimal manner, which typically implies they are all operating at near full-processing capacity.

The load balancer serves as the single point of entry for a WebLogic cluster.

The distribution criteria of a load balancer are based on algorithms applied to the inbound network traffic. The following are some examples:

  • Round-robin—Sends each subsequent client request to the next server in the cluster

  • Least number of users—Redirects client requests to the server that has the least number of users

  • Least amount of traffic—Redirects client requests to the server with the least amount of network traffic

NOTE

The exact available algorithm depends on the capabilities of your load balancer. For example, the WebLogic Server HttpClusterServlet proxy supports only a round-robin algorithm for distributing requests, whereas dedicated load-balancing appliances offer more sophisticated load-balancing algorithms.

The Web Proxy Server

If you have an existing Web tier composed of Netscape, Microsoft, or Apache Web servers, you can leverage this software and hardware layer with a proxy plug-in supplied with WebLogic Server to serve only the static HTTP content of your J2EE application. Dynamic content requests to servlets or JSPs are delegated via the Web Server's proxy plug-in to the servers in the WebLogic cluster that form the Presentation tier. You can also use WebLogic Server as a Web Proxy server by deploying the HttpClusterServlet.

Using a Web Proxyserver does have its advantages because you can leverage the existing infrastructure as well as any firewall policies for the Web tier, which prevents direct connections to the WebLogic cluster. However, having a separate Web tier does involve extra setup and administration activities, and the load-balancing capabilities are constrained to a round-robin type strategy. Also, if clients are primarily accessing dynamic content, having a Web tier will increase the number of network connections required to access the WebLogic cluster, which will affect the latency of a client's response.

WebLogic Server

As illustrated in Figure 25.4, WebLogic Server can be divided into two logical tiers, as follows:

  • Presentation tier—This tier is, in essence, the Web container of WebLogic Server and is responsible for serving the dynamic content of a J2EE application via servlets and JavaServer Pages.

    • NOTE

    If you do not use a Web Proxy server, the Presentation tier also includes the Web tier because it will serve static and dynamic content.

  • Object tier—This tier is, in essence, the EJB container of WebLogic Server, which provides an execution environment for the business logic in a J2EE application via Enterprise JavaBeans.

The DeMilitarized Zone (DMZ)

The DeMilitarized Zone, or DMZ as it is known in the network community, is a perimeter network that is used to protect a specific trusted network environment from direct exposure to an untrusted (external network) environment. To define a DMZ, you first must identify the network environment you need to protect and then identify all the entrance points (front and back doors) to that network. In most cases, the entrance point is a Web server that is connected to the Internet or an untrusted intranet. In such a scenario, the Web server exists in the DMZ.

As you can see in Figure 25.4, you can secure a DMZ by using two firewalls. The one in front of the DMZ should be between the external network (Internet) and your DMZ, which is typically a group of Web servers. The second firewall should be between the DMZ and the internal network.

NOTE

A firewall is typically a hardware appliance that is used to institute a secure access policy for crossing a network's perimeter—for example, allowing only authorized traffic to pass from an untrusted network environment to a DMZ.

Recommended WebLogic Clustering Architectures

Generally, whenever an architectural discussion on how to design a WebLogic cluster occurs, the primary topics that influence the design directly relate to the way the cluster can guarantee the hosted application is very scalable and highly available. However, a WebLogic cluster in conjunction with a load-balancing mechanism, by default, provides a very scalable solution; WebLogic Servers can be added and removed from the cluster transparently to the clients.

Even though clustering is synonymous with both high availability and scalability, your architectural thoughts should be primarily aligned with ensuring a performance-oriented, highly available clustering solution. The following sections discuss two such clustering architectures you can consider: the combined-tier and multi-tier architectures, which differ based on the physical location of the presentation and object tiers.

The Combined-Tier Architecture

The combined-tier architecture, as illustrated in Figure 25.5, combines the Presentation and Object tiers of a J2EE application into a single WebLogic cluster. If a Web Proxy server is not used, the Web tier is also introduced into the cluster.

Figure 25.5Figure 25.5 The combined-tier WebLogic cluster architecture.

This clustering architecture meets the high-availability and scalability requirements for most J2EE applications, with the addition of the following advantages:

  • Ease of administration of the WebLogic cluster because a J2EE application needs to be deployed/undeployed only to and from the same WebLogic cluster using the Administration Console.

  • Optimized local method calls between the Presentation and Object tier. WebLogic Server uses a collocation strategy to optimize method calls to clustered objects (EJB or RMI classes), which prioritizes method calls to objects that are hosted on the same WebLogic Server instance as their replica-aware stub and avoids incurring any additional network overhead. Because all application objects are available locally to each WebLogic Server in the same cluster, the combined-tier architecture presents the best performance for J2EE applications where there is a high frequency of method invocations in the Object tier by the Presentation tier.

The limitation of the combined-tier architecture is that it does not provide an opportunity for introducing load balancing between the Presentation and Object tiers, which may be necessary if the method calls to the Object tier become unbalanced between the servers in the cluster. In such a scenario, the appropriate approach would be to split the Presentation and Object tiers of the J2EE application onto separate physical clusters as in the multi-tier architecture.

The Multi-Tier Architecture

The primary purpose of the multi-tier architecture is to introduce load balancing between the Presentation and Object tiers of a clustered J2EE application. As illustrated in Figure 25.6, this load balancing is achieved by deploying the Presentation and Objects tiers of a J2EE application onto two different clustered servers.

By hosting the Object tier on a dedicated clustered server, WebLogic Servers in the Presentation tier cannot use the collocation optimization strategy for accessing clustered objects.

As depicted in Figure 25.6, however, the Presentation tier does gain the capability to load-balance each method call to a clustered object. In the multi-tier architecture, a servlet acts as the client to the clustered objects. When requests are made to invoke an EJB, the servlet performs a JNDI lookup for the EJB and obtains a replica-aware stub for that bean, which contains the addresses of all servers that host the bean, as well as the load-balancing logic for accessing bean replicas.

NOTE

EJB replica-aware stubs and EJB home load algorithms are specified using elements of the EJB deployment descriptor.

Figure 25.6Figure 25.6 The multi-tier WebLogic cluster architecture.

The following are additional benefits for using the multi-tier architecture:

  • You have more options for load balancing the entire WebLogic cluster without having to scale the Presentation and Object tiers in tandem. For example, if you have a higher frequency of client access to the Presentation tier than the Object tier, you can increase (scale) the number of WebLogic Servers hosting the Presentation tier to a smaller number of Object tier WebLogic Servers.

  • Two clusters present a higher availability option for a J2EE application than just one, as in the case of the combined-tier architecture.

Although the multi-tier clustering architecture provides greater scalability and high-availability options, it does impose the following disadvantages when compared to the combined-tier architecture:

  • Whenever you have to deploy and manage an application over two clusters, it requires twice as much effort as just using one cluster.

  • There is a network overhead for all method calls to clustered objects. You also utilize more IP sockets in the Presentation tier to replicate sessions and connect to WebLogic Servers that host the clustered objects.

  • If you create a DMZ for the Presentation tier by placing a firewall between the Presentation and Object tiers, you will need to bind all WebLogic Servers in the Object tier to public DNS names as opposed to IP addresses because IP address translation problems can occur between the two tiers.

TIP

You can use the Administration Console to set the ExternalDNSName attribute for a WebLogic Server instance, which defines its external DNS name.

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