Welcome!

Weblogic Authors: Elizabeth White, 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
@ThingsExpo has been named the ‘Top WebRTC Influencer' by iTrend. iTrend processes millions of conversations, tweets, interactions, news articles, press releases, blog posts - and extract meaning form them and analyzes mobile and desktop software platforms used to communicate, various metadata (such as geo location), and automation tools. In overall placement, @ThingsExpo ranked as the number one ‘WebRTC Influencer' followed by @DevOpsSummit at 55th.
"There's a growing demand from users for things to be faster. When you think about all the transactions or interactions users will have with your product and everything that is between those transactions and interactions - what drives us at Catchpoint Systems is the idea to measure that and to analyze it," explained Leo Vasiliou, Director of Web Performance Engineering at Catchpoint Systems, in this SYS-CON.tv interview at 18th Cloud Expo, held June 7-9, 2016, at the Javits Center in New York Ci...
The 20th International Cloud Expo has announced that its Call for Papers is open. Cloud Expo, to be held June 6-8, 2017, at the Javits Center in New York City, brings together Cloud Computing, Big Data, Internet of Things, DevOps, Containers, Microservices and WebRTC to one location. With cloud computing driving a higher percentage of enterprise IT budgets every year, it becomes increasingly important to plant your flag in this fast-expanding business opportunity. Submit your speaking proposal ...
20th Cloud Expo, taking place June 6-8, 2017, at the Javits Center in New York City, NY, will feature technical sessions from a rock star conference faculty and the leading industry players in the world. Cloud computing is now being embraced by a majority of enterprises of all sizes. Yesterday's debate about public vs. private has transformed into the reality of hybrid cloud: a recent survey shows that 74% of enterprises have a hybrid cloud strategy.
SYS-CON Events announced today that Linux Academy, the foremost online Linux and cloud training platform and community, will exhibit at SYS-CON's 20th International Cloud Expo®, which will take place on June 6-8, 2017, at the Javits Center in New York City, NY. Linux Academy was founded on the belief that providing high-quality, in-depth training should be available at an affordable price. Industry leaders in quality training, provided services, and student certification passes, its goal is to c...
In the next five to ten years, millions, if not billions of things will become smarter. This smartness goes beyond connected things in our homes like the fridge, thermostat and fancy lighting, and into heavily regulated industries including aerospace, pharmaceutical/medical devices and energy. “Smartness” will embed itself within individual products that are part of our daily lives. We will engage with smart products - learning from them, informing them, and communicating with them. Smart produc...
"What is the next step in the evolution of IoT systems? The answer is data, information, which is a radical shift from assets, from things to input for decision making," stated Michael Minkevich, VP of Technology Services at Luxoft, in this SYS-CON.tv interview at @ThingsExpo, held November 3-5, 2015, at the Santa Clara Convention Center in Santa Clara, CA.
The emerging Internet of Everything creates tremendous new opportunities for customer engagement and business model innovation. However, enterprises must overcome a number of critical challenges to bring these new solutions to market. In his session at @ThingsExpo, Michael Martin, CTO/CIO at nfrastructure, outlined these key challenges and recommended approaches for overcoming them to achieve speed and agility in the design, development and implementation of Internet of Everything solutions with...
WebRTC sits at the intersection between VoIP and the Web. As such, it poses some interesting challenges for those developing services on top of it, but also for those who need to test and monitor these services. In his session at WebRTC Summit, Tsahi Levent-Levi, co-founder of testRTC, reviewed the various challenges posed by WebRTC when it comes to testing and monitoring and on ways to overcome them.
Internet of @ThingsExpo, taking place June 6-8, 2017 at the Javits Center in New York City, New York, is co-located with the 20th International Cloud Expo and will feature technical sessions from a rock star conference faculty and the leading industry players in the world. @ThingsExpo New York Call for Papers is now open.
Smart Cities are here to stay, but for their promise to be delivered, the data they produce must not be put in new siloes. In his session at @ThingsExpo, Mathias Herberts, Co-founder and CTO of Cityzen Data, discussed the best practices that will ensure a successful smart city journey.
Every successful software product evolves from an idea to an enterprise system. Notably, the same way is passed by the product owner's company. In his session at 20th Cloud Expo, Oleg Lola, CEO of MobiDev, will provide a generalized overview of the evolution of a software product, the product owner, the needs that arise at various stages of this process, and the value brought by a software development partner to the product owner as a response to these needs.
In 2014, Amazon announced a new form of compute called Lambda. We didn't know it at the time, but this represented a fundamental shift in what we expect from cloud computing. Now, all of the major cloud computing vendors want to take part in this disruptive technology. In his session at 20th Cloud Expo, John Jelinek IV, a web developer at Linux Academy, will discuss why major players like AWS, Microsoft Azure, IBM Bluemix, and Google Cloud Platform are all trying to sidestep VMs and containers...
SYS-CON Events announced today that MobiDev, a client-oriented software development company, will exhibit at SYS-CON's 20th International Cloud Expo®, which will take place June 6-8, 2017, at the Javits Center in New York City, NY, and the 21st International Cloud Expo®, which will take place October 31-November 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. MobiDev is a software company that develops and delivers turn-key mobile apps, websites, web services, and complex softw...
The cloud market growth today is largely in public clouds. While there is a lot of spend in IT departments in virtualization, these aren’t yet translating into a true “cloud” experience within the enterprise. What is stopping the growth of the “private cloud” market? In his general session at 18th Cloud Expo, Nara Rajagopalan, CEO of Accelerite, explored the challenges in deploying, managing, and getting adoption for a private cloud within an enterprise. What are the key differences between wh...
"Tintri was started in 2008 with the express purpose of building a storage appliance that is ideal for virtualized environments. We support a lot of different hypervisor platforms from VMware to OpenStack to Hyper-V," explained Dan Florea, Director of Product Management at Tintri, in this SYS-CON.tv interview at 18th Cloud Expo, held June 7-9, 2016, at the Javits Center in New York City, NY.
The security needs of IoT environments require a strong, proven approach to maintain security, trust and privacy in their ecosystem. Assurance and protection of device identity, secure data encryption and authentication are the key security challenges organizations are trying to address when integrating IoT devices. This holds true for IoT applications in a wide range of industries, for example, healthcare, consumer devices, and manufacturing. In his session at @ThingsExpo, Lancen LaChance, vic...
WebRTC has had a real tough three or four years, and so have those working with it. Only a few short years ago, the development world were excited about WebRTC and proclaiming how awesome it was. You might have played with the technology a couple of years ago, only to find the extra infrastructure requirements were painful to implement and poorly documented. This probably left a bitter taste in your mouth, especially when things went wrong.
Big Data, cloud, analytics, contextual information, wearable tech, sensors, mobility, and WebRTC: together, these advances have created a perfect storm of technologies that are disrupting and transforming classic communications models and ecosystems. In his session at @ThingsExpo, Erik Perotti, Senior Manager of New Ventures on Plantronics’ Innovation team, provided an overview of this technological shift, including associated business and consumer communications impacts, and opportunities it m...
You have great SaaS business app ideas. You want to turn your idea quickly into a functional and engaging proof of concept. You need to be able to modify it to meet customers' needs, and you need to deliver a complete and secure SaaS application. How could you achieve all the above and yet avoid unforeseen IT requirements that add unnecessary cost and complexity? You also want your app to be responsive in any device at any time. In his session at 19th Cloud Expo, Mark Allen, General Manager of...