|By Sudhir Upadhyay||
|August 8, 2005 12:00 PM EDT||
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.
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 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.
|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|
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?
The best-practices for building IoT applications with Go Code that attendees can use to build their own IoT applications. In his session at @ThingsExpo, Indraneel Mitra, Senior Solutions Architect & Technology Evangelist at Cognizant, provided valuable information and resources for both novice and experienced developers on how to get started with IoT and Golang in a day. He also provided information on how to use Intel Arduino Kit, Go Robotics API and AWS IoT stack to build an application tha...
Jul. 28, 2016 12:00 PM EDT Reads: 1,213
IoT generates lots of temporal data. But how do you unlock its value? You need to discover patterns that are repeatable in vast quantities of data, understand their meaning, and implement scalable monitoring across multiple data streams in order to monetize the discoveries and insights. Motif discovery and deep learning platforms are emerging to visualize sensor data, to search for patterns and to build application that can monitor real time streams efficiently. In his session at @ThingsExpo, ...
Jul. 28, 2016 11:15 AM EDT Reads: 1,124
SYS-CON Events announced today that LeaseWeb USA, a cloud Infrastructure-as-a-Service (IaaS) provider, will exhibit at the 19th International Cloud Expo, which will take place on November 1–3, 2016, at the Santa Clara Convention Center in Santa Clara, CA. LeaseWeb is one of the world's largest hosting brands. The company helps customers define, develop and deploy IT infrastructure tailored to their exact business needs, by combining various kinds cloud solutions.
Jul. 28, 2016 10:45 AM EDT Reads: 1,262
SYS-CON Events announced today that 910Telecom will exhibit at the 19th International Cloud Expo, which will take place on November 1–3, 2016, at the Santa Clara Convention Center in Santa Clara, CA. Housed in the classic Denver Gas & Electric Building, 910 15th St., 910Telecom is a carrier-neutral telecom hotel located in the heart of Denver. Adjacent to CenturyLink, AT&T, and Denver Main, 910Telecom offers connectivity to all major carriers, Internet service providers, Internet backbones and ...
Jul. 28, 2016 10:30 AM EDT Reads: 775
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 ...
Jul. 28, 2016 10:00 AM EDT Reads: 272
SYS-CON Events announced today that Venafi, the Immune System for the Internet™ and the leading provider of Next Generation Trust Protection, will exhibit at @DevOpsSummit at 19th International Cloud Expo, which will take place on November 1–3, 2016, at the Santa Clara Convention Center in Santa Clara, CA. Venafi is the Immune System for the Internet™ that protects the foundation of all cybersecurity – cryptographic keys and digital certificates – so they can’t be misused by bad guys in attacks...
Jul. 28, 2016 09:30 AM EDT Reads: 1,402
It’s 2016: buildings are smart, connected and the IoT is fundamentally altering how control and operating systems work and speak to each other. Platforms across the enterprise are networked via inexpensive sensors to collect massive amounts of data for analytics, information management, and insights that can be used to continuously improve operations. In his session at @ThingsExpo, Brian Chemel, Co-Founder and CTO of Digital Lumens, will explore: The benefits sensor-networked systems bring to ...
Jul. 28, 2016 09:00 AM EDT Reads: 1,607
Manufacturers are embracing the Industrial Internet the same way consumers are leveraging Fitbits – to improve overall health and wellness. Both can provide consistent measurement, visibility, and suggest performance improvements customized to help reach goals. Fitbit users can view real-time data and make adjustments to increase their activity. In his session at @ThingsExpo, Mark Bernardo Professional Services Leader, Americas, at GE Digital, discussed how leveraging the Industrial Internet a...
Jul. 28, 2016 07:30 AM EDT Reads: 531
There will be new vendors providing applications, middleware, and connected devices to support the thriving IoT ecosystem. This essentially means that electronic device manufacturers will also be in the software business. Many will be new to building embedded software or robust software. This creates an increased importance on software quality, particularly within the Industrial Internet of Things where business-critical applications are becoming dependent on products controlled by software. Qua...
Jul. 28, 2016 06:45 AM EDT Reads: 1,568
In addition to all the benefits, IoT is also bringing new kind of customer experience challenges - cars that unlock themselves, thermostats turning houses into saunas and baby video monitors broadcasting over the internet. This list can only increase because while IoT services should be intuitive and simple to use, the delivery ecosystem is a myriad of potential problems as IoT explodes complexity. So finding a performance issue is like finding the proverbial needle in the haystack.
Jul. 28, 2016 05:45 AM EDT Reads: 2,329
The 19th International Cloud Expo has announced that its Call for Papers is open. Cloud Expo, to be held November 1-3, 2016, at the Santa Clara Convention Center in Santa Clara, CA, brings together Cloud Computing, Big Data, Internet of Things, DevOps, Digital Transformation, 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 opportuni...
Jul. 28, 2016 03:15 AM EDT Reads: 2,653
Large scale deployments present unique planning challenges, system commissioning hurdles between IT and OT and demand careful system hand-off orchestration. In his session at @ThingsExpo, Jeff Smith, Senior Director and a founding member of Incenergy, will discuss some of the key tactics to ensure delivery success based on his experience of the last two years deploying Industrial IoT systems across four continents.
Jul. 28, 2016 03:00 AM EDT Reads: 1,645
The Internet of Things will challenge the status quo of how IT and development organizations operate. Or will it? Certainly the fog layer of IoT requires special insights about data ontology, security and transactional integrity. But the developmental challenges are the same: People, Process and Platform. In his session at @ThingsExpo, Craig Sproule, CEO of Metavine, demonstrated how to move beyond today's coding paradigm and shared the must-have mindsets for removing complexity from the develo...
Jul. 28, 2016 02:30 AM EDT Reads: 1,563
SYS-CON Events announced today that MangoApps will exhibit at the 19th International Cloud Expo, which will take place on November 1–3, 2016, at the Santa Clara Convention Center in Santa Clara, CA. MangoApps provides modern company intranets and team collaboration software, allowing workers to stay connected and productive from anywhere in the world and from any device.
Jul. 28, 2016 02:15 AM EDT Reads: 1,421
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...
Jul. 28, 2016 02:00 AM EDT Reads: 2,069
The IETF draft standard for M2M certificates is a security solution specifically designed for the demanding needs of IoT/M2M applications. In his session at @ThingsExpo, Brian Romansky, VP of Strategic Technology at TrustPoint Innovation, explained how M2M certificates can efficiently enable confidentiality, integrity, and authenticity on highly constrained devices.
Jul. 28, 2016 01:45 AM EDT Reads: 1,125
In today's uber-connected, consumer-centric, cloud-enabled, insights-driven, multi-device, global world, the focus of solutions has shifted from the product that is sold to the person who is buying the product or service. Enterprises have rebranded their business around the consumers of their products. The buyer is the person and the focus is not on the offering. The person is connected through multiple devices, wearables, at home, on the road, and in multiple locations, sometimes simultaneously...
Jul. 28, 2016 01:15 AM EDT Reads: 881
“delaPlex Software provides software outsourcing services. We have a hybrid model where we have onshore developers and project managers that we can place anywhere in the U.S. or in Europe,” explained Manish Sachdeva, CEO at delaPlex Software, in this SYS-CON.tv interview at @ThingsExpo, held June 7-9, 2016, at the Javits Center in New York City, NY.
Jul. 28, 2016 01:00 AM EDT Reads: 1,641
"We've discovered that after shows 80% if leads that people get, 80% of the conversations end up on the show floor, meaning people forget about it, people forget who they talk to, people forget that there are actual business opportunities to be had here so we try to help out and keep the conversations going," explained Jeff Mesnik, Founder and President of ContentMX, in this SYS-CON.tv interview at 18th Cloud Expo, held June 7-9, 2016, at the Javits Center in New York City, NY.
Jul. 27, 2016 10:30 PM EDT Reads: 1,424
Internet of @ThingsExpo, taking place November 1-3, 2016, at the Santa Clara Convention Center in Santa Clara, CA, is co-located with the 19th International Cloud Expo and will feature technical sessions from a rock star conference faculty and the leading industry players in the world and ThingsExpo Silicon Valley Call for Papers is now open.
Jul. 27, 2016 10:00 PM EDT Reads: 2,689