Welcome!

Weblogic Authors: Michael Meiner, Michael Bushong, Avi Rosenthal

Related Topics: Weblogic

Weblogic: Article

Failover and Recovery of Enterprise Applications - Part 1

High availability - moving beyond clustering

In enterprise application architecture, it is naïve to assume that none of the software/hardware components will go down. In fact, most of the IT managers and architects acknowledge this. However, a well-tested and robust recovery procedure continues to take a back seat when designing and implementing software projects. In several scenarios, administrators end up performing basic failover testing by shutting down the processes and verifying that the subsequent requests succeeded.

Although this level of testing can satisfy the failover requirements for the records, more robust failover testing needs to be performed to ensure a proper recovery if failures do occur. One of the primary reasons for the lack of robust recovery and well-tested procedures can be attributed to a high degree of reliance on the application server's in-built failover capabilities. While it is true that most of the popular application servers boost their clustering and associated high-availability features, it is equally important that system architects need to go beyond those features for an end-to-end high availability of the application. This article suggests how good planning, robust scripting, and a well- thought-out application design, along with application server facilities, can provide a highly available environment for the entire application. In the first article in a series of three, I will cover the basic high-availability options available while deploying a J2EE application on WebLogic Server.

Before diving into specifics, it is important to understand some of the commonly used terms when one talks about high-availability.

High Availability - So, what does high availability really mean? From a user's point of view, it means an application that is always available to perform the user's transactions. In other words, even though one or more of the back-end system becomes unavailable, the application may be architected in such a manner that these failures are not visible to the end user. High availability is a relative term - for some applications, there is high availability only if the site is never down - or zero downtime. For some applications it should be available, without interruptions - during the normal business operations. How and when a system is called highly available is typically defined by SLA - Service Level Agreements. Each organization may have its own system level agreements for the nonavailability of the applications during certain maintenance windows.

Transparent Failover - A highly available system does not necessarily imply that failover is always transparent. In other words, when one of the components within the application fails, the subsequent requests get routed to other available servers, thereby making it highly available. However it is possible for users to lose their sessions. There may even be a loss of data during the failure and things of that nature. In these cases, even though the system is available for subsequent requests, none of the above scenarios truly represents a transparent failover within an enterprise application.

Fault Tolerance - Fault tolerance is the system's ability to keep the system available and maintain data consistency in case of failure in one or more of its software components.

Clustering - Perhaps the most common term used in conjunction with HA, clustering is essentially a service provided by application servers in which multiple servers run as a group. The clustering service is responsible for load balancing the user requests and also for rerouting the incoming traffic to available servers should one of the servers in the cluster become unavailable.

Recovery - The ability of the system to recover itself from a failure condition as well as to bring the state of the objects into their pre-failure condition.

Failure Points
In an enterprise application, there are several points of failure - both within each individual component and at integration touch points with other components and interfaces. As the number of interfaces increases, the failover and recovery procedures become increasingly complex due to interdependencies involved. Although each component within the application may have recovery procedures for itself, the problem arises when one component or a combination of components within the system fails simultaneously.

So, a first step in designing a highly available enterprise system is identifying all of the possible permutations and combinations of failure points within the system. The identification process should involve all of the components within the system - application, network, hardware, and database - each and every component involved. As one begins to create such a matrix, it becomes overly complicated as the number of components and products that are mixing increases. This article will serve to focus failover and recovery of components and applications within the WebLogic Platform.

WebLogic Platform
WebLogic Server - WebLogic Server provides a number of J2EE services that include Java Messaging Service (JMS), Transactions (JTS/JTA) and Security, Servlet Engine, EJB container, and so forth. When designing enterprise applications for high availability it is crucial that architects have a good understanding of how these services failover when one of the instances hosting them goes down. A thorough understanding of the failover and recovery procedures of these services is also critical in automating the recovery of a downed instance or a system.

Clustering Overview - Perhaps no discussion on WLS high availability is complete without touching on WebLogic Clustering. An application that is deployed homogenously in a cluster is generally highly available. When one of the server instances goes down, the request is routed to the other available server in the cluster. In fact, the concept of the cluster is not new to J2EE architects and WebLogic Server administrators. Readers of this article are encouraged to review the WebLogic Server clustering documentation (http://e-docs.bea.com/wls/docs81/cluster/index.html). Essentially, most of the services provided by WebLogic can be categorized as either clusterable (i.e., multiple instances of these run on different services on multiple servers), or nonclusterable (there may be multiple instances of these services configured, but only one is active at a given time within the cluster). More information on which services can be clustered is provided in WebLogic Server documentation. Table 1 lists the clustered and nonclustered services in WebLogic Platform 8.1.

More Stories By Sudhir Upadhyay

Sudhir Upadhyay is currently with Architecture and Shared services at JP Morgan Chase where he is an application architect. Prior to joining JPMorgan, he was a principal consultant with BEA Professional Services where he helped customers design and implement enterprise J2EE solutions. He is a BEA Certified WebLogic Developer and a Sun Certified Java Developer.

Comments (2) View Comments

Share your thoughts on this story.

Add your comment
You must be signed in to add a comment. Sign-in | Register

In accordance with our Comment Policy, we encourage comments that are on topic, relevant and to-the-point. We will remove comments that include profanity, personal attacks, racial slurs, threats of violence, or other inappropriate material that violates our Terms and Conditions, and will block users who make repeated violations. We ask all readers to expect diversity of opinion and to treat one another with dignity and respect.


Most Recent Comments
Thirunavukarasu 02/04/06 06:31:00 AM EST

A neatly explained technical atricle. Very useful, very crisp. Thanks .

Viktor Lioutyi 08/12/05 10:34:27 AM EDT

Hi,

How to test failover in automatic manner?

"In several scenarios, administrators end up performing basic failover testing by shutting down the processes and verifying that the subsequent requests succeeded.

Although this level of testing can satisfy the failover requirements for the records, more robust failover testing needs to be performed to ensure a proper recovery if failures do occur."

We did the manual testing and failover worked. But we would like to do automatic testing of failover to make sure that it works for all our 1000+ pages. BEA does not have any tool for such testing.

There are different reasons why someone may want to test all pages for failover.

1) WebLogic only replicates attributes that were modified. Call of session's setAttribute() method is an indication for WebLogic that attribute was modified. This call may be done explicitly or implicitly when jsp tags are used. It is possible that on some pages members of complex attributes were modified but WebLogic was not notified about it, so it will not replicate such attributes.

2) Complex attributes may reference other objects and attributes. After replication these references may be broken. For example, attribute A and B references object C. Only attribute A was modified, so only A will be replicated. After the replication A and B may point to different copies of C and program may not work correctly anymore.

3) Some objects are assumed to be singletons. Developer needs to provide special implementation for serialization to support replication of singleton objects. If this implementation is omitted, then replication may create copies of a singleton object.

4) Transient fields are not going to be replicated but there should be a recovery code that restores values of these fields after replication. Without testing we do not know if all our recovery code works correctly or not.

There are probably other reasons too.

Does anybody know about any tool for automatic testing of failover (or at least just session replication) for WebLogic and/or WebSphere?

Thanks,
Viktor

@ThingsExpo Stories
The BPM world is going through some evolution or changes where traditional business process management solutions really have nowhere to go in terms of development of the road map. In this demo at 15th Cloud Expo, Kyle Hansen, Director of Professional Services at AgilePoint, shows AgilePoint’s unique approach to dealing with this market circumstance by developing a rapid application composition or development framework.

ARMONK, N.Y., Nov. 20, 2014 /PRNewswire/ --  IBM (NYSE: IBM) today announced that it is bringing a greater level of control, security and flexibility to cloud-based application development and delivery with a single-tenant version of Bluemix, IBM's platform-as-a-service. The new platform enables developers to build ap...

"BSQUARE is in the business of selling software solutions for smart connected devices. It's obvious that IoT has moved from being a technology to being a fundamental part of business, and in the last 18 months people have said let's figure out how to do it and let's put some focus on it, " explained Dave Wagstaff, VP & Chief Architect, at BSQUARE Corporation, in this SYS-CON.tv interview at @ThingsExpo, held Nov 4-6, 2014, at the Santa Clara Convention Center in Santa Clara, CA.
The major cloud platforms defy a simple, side-by-side analysis. Each of the major IaaS public-cloud platforms offers their own unique strengths and functionality. Options for on-site private cloud are diverse as well, and must be designed and deployed while taking existing legacy architecture and infrastructure into account. Then the reality is that most enterprises are embarking on a hybrid cloud strategy and programs. In this Power Panel at 15th Cloud Expo (http://www.CloudComputingExpo.com), moderated by Ashar Baig, Research Director, Cloud, at Gigaom Research, Nate Gordon, Director of T...
The Internet of Things is not new. Historically, smart businesses have used its basic concept of leveraging data to drive better decision making and have capitalized on those insights to realize additional revenue opportunities. So, what has changed to make the Internet of Things one of the hottest topics in tech? In his session at @ThingsExpo, Chris Gray, Director, Embedded and Internet of Things, discussed the underlying factors that are driving the economics of intelligent systems. Discover how hardware commoditization, the ubiquitous nature of connectivity, and the emergence of Big Data a...
SYS-CON Events announced today that Windstream, a leading provider of advanced network and cloud communications, has been named “Silver Sponsor” of SYS-CON's 16th International Cloud Expo®, which will take place on June 9–11, 2015, at the Javits Center in New York, NY. Windstream (Nasdaq: WIN), a FORTUNE 500 and S&P 500 company, is a leading provider of advanced network communications, including cloud computing and managed services, to businesses nationwide. The company also offers broadband, phone and digital TV services to consumers primarily in rural areas.
“In the past year we've seen a lot of stabilization of WebRTC. You can now use it in production with a far greater degree of certainty. A lot of the real developments in the past year have been in things like the data channel, which will enable a whole new type of application," explained Peter Dunkley, Technical Director at Acision, in this SYS-CON.tv interview at @ThingsExpo, held Nov 4–6, 2014, at the Santa Clara Convention Center in Santa Clara, CA.
SYS-CON Events announced today that IDenticard will exhibit at SYS-CON's 16th International Cloud Expo®, which will take place on June 9-11, 2015, at the Javits Center in New York City, NY. IDenticard™ is the security division of Brady Corp (NYSE: BRC), a $1.5 billion manufacturer of identification products. We have small-company values with the strength and stability of a major corporation. IDenticard offers local sales, support and service to our customers across the United States and Canada. Our partner network encompasses some 300 of the world's leading systems integrators and security s...
DevOps Summit 2015 New York, co-located with the 16th International Cloud Expo - to be held June 9-11, 2015, at the Javits Center in New York City, NY - announces that it is now accepting Keynote Proposals. The widespread success of cloud computing is driving the DevOps revolution in enterprise IT. Now as never before, development teams must communicate and collaborate in a dynamic, 24/7/365 environment. There is no time to wait for long development cycles that produce software that is obsolete at launch. DevOps may be disruptive, but it is essential.
"People are a lot more knowledgeable about APIs now. There are two types of people who work with APIs - IT people who want to use APIs for something internal and the product managers who want to do something outside APIs for people to connect to them," explained Roberto Medrano, Executive Vice President at SOA Software, in this SYS-CON.tv interview at Cloud Expo, held Nov 4–6, 2014, at the Santa Clara Convention Center in Santa Clara, CA.
Nigeria has the largest economy in Africa, at more than US$500 billion, and ranks 23rd in the world. A recent re-evaluation of Nigeria's true economic size doubled the previous estimate, and brought it well ahead of South Africa, which is a member (unlike Nigeria) of the G20 club for political as well as economic reasons. Nigeria's economy can be said to be quite diverse from one point of view, but heavily dependent on oil and gas at the same time. Oil and natural gas account for about 15% of Nigera's overall economy, but traditionally represent more than 90% of the country's exports and as...
The Internet of Things is a misnomer. That implies that everything is on the Internet, and that simply should not be - especially for things that are blurring the line between medical devices that stimulate like a pacemaker and quantified self-sensors like a pedometer or pulse tracker. The mesh of things that we manage must be segmented into zones of trust for sensing data, transmitting data, receiving command and control administrative changes, and peer-to-peer mesh messaging. In his session at @ThingsExpo, Ryan Bagnulo, Solution Architect / Software Engineer at SOA Software, focused on desi...
"At our booth we are showing how to provide trust in the Internet of Things. Trust is where everything starts to become secure and trustworthy. Now with the scaling of the Internet of Things it becomes an interesting question – I've heard numbers from 200 billion devices next year up to a trillion in the next 10 to 15 years," explained Johannes Lintzen, Vice President of Sales at Utimaco, in this SYS-CON.tv interview at @ThingsExpo, held Nov 4–6, 2014, at the Santa Clara Convention Center in Santa Clara, CA.
"For over 25 years we have been working with a lot of enterprise customers and we have seen how companies create applications. And now that we have moved to cloud computing, mobile, social and the Internet of Things, we see that the market needs a new way of creating applications," stated Jesse Shiah, CEO, President and Co-Founder of AgilePoint Inc., in this SYS-CON.tv interview at 15th Cloud Expo, held Nov 4–6, 2014, at the Santa Clara Convention Center in Santa Clara, CA.
SYS-CON Events announced today that Gridstore™, the leader in hyper-converged infrastructure purpose-built to optimize Microsoft workloads, will exhibit at SYS-CON's 16th International Cloud Expo®, which will take place on June 9-11, 2015, at the Javits Center in New York City, NY. Gridstore™ is the leader in hyper-converged infrastructure purpose-built for Microsoft workloads and designed to accelerate applications in virtualized environments. Gridstore’s hyper-converged infrastructure is the industry’s first all flash version of HyperConverged Appliances that include both compute and storag...
Today’s enterprise is being driven by disruptive competitive and human capital requirements to provide enterprise application access through not only desktops, but also mobile devices. To retrofit existing programs across all these devices using traditional programming methods is very costly and time consuming – often prohibitively so. In his session at @ThingsExpo, Jesse Shiah, CEO, President, and Co-Founder of AgilePoint Inc., discussed how you can create applications that run on all mobile devices as well as laptops and desktops using a visual drag-and-drop application – and eForms-buildi...
We certainly live in interesting technological times. And no more interesting than the current competing IoT standards for connectivity. Various standards bodies, approaches, and ecosystems are vying for mindshare and positioning for a competitive edge. It is clear that when the dust settles, we will have new protocols, evolved protocols, that will change the way we interact with devices and infrastructure. We will also have evolved web protocols, like HTTP/2, that will be changing the very core of our infrastructures. At the same time, we have old approaches made new again like micro-services...
Code Halos - aka "digital fingerprints" - are the key organizing principle to understand a) how dumb things become smart and b) how to monetize this dynamic. In his session at @ThingsExpo, Robert Brown, AVP, Center for the Future of Work at Cognizant Technology Solutions, outlined research, analysis and recommendations from his recently published book on this phenomena on the way leading edge organizations like GE and Disney are unlocking the Internet of Things opportunity and what steps your organization should be taking to position itself for the next platform of digital competition.
The 3rd International Internet of @ThingsExpo, co-located with the 16th International Cloud Expo - to be held June 9-11, 2015, at the Javits Center in New York City, NY - announces that its Call for Papers is now open. The Internet of Things (IoT) is the biggest idea since the creation of the Worldwide Web more than 20 years ago.
As the Internet of Things unfolds, mobile and wearable devices are blurring the line between physical and digital, integrating ever more closely with our interests, our routines, our daily lives. Contextual computing and smart, sensor-equipped spaces bring the potential to walk through a world that recognizes us and responds accordingly. We become continuous transmitters and receivers of data. In his session at @ThingsExpo, Andrew Bolwell, Director of Innovation for HP's Printing and Personal Systems Group, discussed how key attributes of mobile technology – touch input, sensors, social, and ...