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
"delaPlex is a software development company. We do team-based outsourcing development," explained Mark Rivers, COO and Co-founder of delaPlex Software, in this SYS-CON.tv interview at 18th Cloud Expo, held June 7-9, 2016, at the Javits Center in New York City, NY.
IoT is rapidly changing the way enterprises are using data to improve business decision-making. In order to derive business value, organizations must unlock insights from the data gathered and then act on these. In their session at @ThingsExpo, Eric Hoffman, Vice President at EastBanc Technologies, and Peter Shashkin, Head of Development Department at EastBanc Technologies, discussed how one organization leveraged IoT, cloud technology and data analysis to improve customer experiences and effi...
The IoT is changing the way enterprises conduct business. In his session at @ThingsExpo, Eric Hoffman, Vice President at EastBanc Technologies, discussed how businesses can gain an edge over competitors by empowering consumers to take control through IoT. He cited examples such as a Washington, D.C.-based sports club that leveraged IoT and the cloud to develop a comprehensive booking system. He also highlighted how IoT can revitalize and restore outdated business models, making them profitable ...
There are several IoTs: the Industrial Internet, Consumer Wearables, Wearables and Healthcare, Supply Chains, and the movement toward Smart Grids, Cities, Regions, and Nations. There are competing communications standards every step of the way, a bewildering array of sensors and devices, and an entire world of competing data analytics platforms. To some this appears to be chaos. In this power panel at @ThingsExpo, moderated by Conference Chair Roger Strukhoff, Bradley Holt, Developer Advocate a...
A strange thing is happening along the way to the Internet of Things, namely far too many devices to work with and manage. It has become clear that we'll need much higher efficiency user experiences that can allow us to more easily and scalably work with the thousands of devices that will soon be in each of our lives. Enter the conversational interface revolution, combining bots we can literally talk with, gesture to, and even direct with our thoughts, with embedded artificial intelligence, wh...
Machine Learning helps make complex systems more efficient. By applying advanced Machine Learning techniques such as Cognitive Fingerprinting, wind project operators can utilize these tools to learn from collected data, detect regular patterns, and optimize their own operations. In his session at 18th Cloud Expo, Stuart Gillen, Director of Business Development at SparkCognition, discussed how research has demonstrated the value of Machine Learning in delivering next generation analytics to imp...
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...
Connected devices and the industrial internet are growing exponentially every year with Cisco expecting 50 billion devices to be in operation by 2020. In this period of growth, location-based insights are becoming invaluable to many businesses as they adopt new connected technologies. Knowing when and where these devices connect from is critical for a number of scenarios in supply chain management, disaster management, emergency response, M2M, location marketing and more. In his session at @Th...
Basho Technologies has announced the latest release of Basho Riak TS, version 1.3. Riak TS is an enterprise-grade NoSQL database optimized for Internet of Things (IoT). The open source version enables developers to download the software for free and use it in production as well as make contributions to the code and develop applications around Riak TS. Enhancements to Riak TS make it quick, easy and cost-effective to spin up an instance to test new ideas and build IoT applications. In addition to...
When people aren’t talking about VMs and containers, they’re talking about serverless architecture. Serverless is about no maintenance. It means you are not worried about low-level infrastructural and operational details. An event-driven serverless platform is a great use case for IoT. In his session at @ThingsExpo, Animesh Singh, an STSM and Lead for IBM Cloud Platform and Infrastructure, will detail how to build a distributed serverless, polyglot, microservices framework using open source tec...
Apixio Inc. has raised $19.3 million in Series D venture capital funding led by SSM Partners with participation from First Analysis, Bain Capital Ventures and Apixio’s largest angel investor. Apixio will dedicate the proceeds toward advancing and scaling products powered by its cognitive computing platform, further enabling insights for optimal patient care. The Series D funding comes as Apixio experiences strong momentum and increasing demand for its HCC Profiler solution, which mines unstruc...
IoT offers a value of almost $4 trillion to the manufacturing industry through platforms that can improve margins, optimize operations & drive high performance work teams. By using IoT technologies as a foundation, manufacturing customers are integrating worker safety with manufacturing systems, driving deep collaboration and utilizing analytics to exponentially increased per-unit margins. However, as Benoit Lheureux, the VP for Research at Gartner points out, “IoT project implementers often ...
It is one thing to build single industrial IoT applications, but what will it take to build the Smart Cities and truly society changing applications of the future? The technology won’t be the problem, it will be the number of parties that need to work together and be aligned in their motivation to succeed. In his Day 2 Keynote at @ThingsExpo, Henrik Kenani Dahlgren, Portfolio Marketing Manager at Ericsson, discussed how to plan to cooperate, partner, and form lasting all-star teams to change t...
In his general session at 18th Cloud Expo, Lee Atchison, Principal Cloud Architect and Advocate at New Relic, discussed cloud as a ‘better data center’ and how it adds new capacity (faster) and improves application availability (redundancy). The cloud is a ‘Dynamic Tool for Dynamic Apps’ and resource allocation is an integral part of your application architecture, so use only the resources you need and allocate /de-allocate resources on the fly.
Presidio has received the 2015 EMC Partner Services Quality Award from EMC Corporation for achieving outstanding service excellence and customer satisfaction as measured by the EMC Partner Services Quality (PSQ) program. Presidio was also honored as the 2015 EMC Americas Marketing Excellence Partner of the Year and 2015 Mid-Market East Partner of the Year. The EMC PSQ program is a project-specific survey program designed for partners with Service Partner designations to solicit customer feedbac...
In his keynote at 18th Cloud Expo, Andrew Keys, Co-Founder of ConsenSys Enterprise, provided an overview of the evolution of the Internet and the Database and the future of their combination – the Blockchain. Andrew Keys is Co-Founder of ConsenSys Enterprise. He comes to ConsenSys Enterprise with capital markets, technology and entrepreneurial experience. Previously, he worked for UBS investment bank in equities analysis. Later, he was responsible for the creation and distribution of life sett...
Cloud computing is being adopted in one form or another by 94% of enterprises today. Tens of billions of new devices are being connected to The Internet of Things. And Big Data is driving this bus. An exponential increase is expected in the amount of information being processed, managed, analyzed, and acted upon by enterprise IT. This amazing is not part of some distant future - it is happening today. One report shows a 650% increase in enterprise data by 2020. Other estimates are even higher....
SYS-CON Events announced today that Bsquare has been named “Silver Sponsor” of SYS-CON's @ThingsExpo, which will take place on November 1–3, 2016, at the Santa Clara Convention Center in Santa Clara, CA. For more than two decades, Bsquare has helped its customers extract business value from a broad array of physical assets by making them intelligent, connecting them, and using the data they generate to optimize business processes.
Internet of @ThingsExpo, taking place November 1-3, 2016, at the Santa Clara Convention Center in Santa Clara, CA, is co-located with 19th Cloud Expo and will feature technical sessions from a rock star conference faculty and the leading industry players in the world. The Internet of Things (IoT) is the most profound change in personal and enterprise IT since the creation of the Worldwide Web more than 20 years ago. All major researchers estimate there will be tens of billions devices - comp...
19th Cloud Expo, taking place November 1-3, 2016, at the Santa Clara Convention Center in Santa Clara, CA, 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. Meanwhile, 94% of enterpri...