Welcome!

Open Web Authors: Liz McMillan, Lori MacVittie, Gilad Parann-Nissany, Carmen Gonzalez, Mark R. Hinkle

Related Topics: Java

Java: Article

Making the Impossible Easy: Failover for Any Application

Using JDBC Database Connectivity Drivers to Support Your Application Failover Strategy

JDBC at Cloud Expo

If your systems require constant accessibility, you know that application failover is an essential function for automatically and transparently redirecting requests to an alternate server in the case of a failure or downtime. Several options exist for ensuring high availability for your mission-critical applications. Those options may be hardware- or software-based, and may also vary considerably in terms of project or enterprise scope and in terms of cost and complexity. Chances are you're relying on one or more such options. But are you aware that the database driver software you use can make application failover much easier and cost-effective to implement, configure, and manage application failover?

High availability solutions are typically complicated and expensive to code. With an application relying on an Oracle data source platform, for example, the Transparent Application Failover (TAF) is what Oracle offers as a high availability strategy. This is certainly a robust solution; however, it must operate in conjunction with Oracle's Real Application Cluster (RAC) high availability environment. An existing application using a non-RAC replication solution cannot use TAF. Implementing Oracle's RAC environment is expensive, and to get an application to support TAF you'll be faced with writing a great deal of complicated, Oracle-specific code.

As an alternative option, you could implement, configure, and manage your application failover entirely through the JDBC software driver used to access the Oracle database. Drivers exist on the market that provide sophisticated failover capabilities such as replaying Select queries in progress and re-creating lost connections and sessions. This approach obviously offers advantages over a proprietary failover approach requiring database-specific application code and offering limited database-related flexibility going forward. But is a driver-based solution really up to the job?

Putting It to the Test
To demonstrate how you might implement a JDBC driver-based application failover, I prepared a use case example of the technology using a small Java application and a high-performance commercially available JDBC driver connecting to an Oracle database. In this demo, a company is writing a web application to browse through a number of golf courses. The country clubs that the company is working for expect a seamless experience for their users (i.e., the application is low tolerance). The data is replicated on two different servers and users get to browse through the course catalog (a page per course), and each page displays course information from the database. The developer wants to ensure that the application doesn't experience any errors or hiccups while a user is browsing the catalog. They want to ensure that, should the database connection to the primary server fail while fetching Course 5, users get Course 6 - rather than an error - when they hit the next button.

Having set up my primary database and replicating the data on my alternate database, I was ready to test failover. Since physically pulling the cable on or actually crashing the server running the primary database would have provoked undesirable responses from my co-workers, I employed a freely available packet analyzer (sniffer) utility called Snoop. It's designed to gather data about the wire-level traffic between the driver and server; however, it can also be used to simulate a database failure. Simply starting a Snoop program sitting between the application and primary sever and then killing the window running Snoop effectively terminates the connection by destroying the active socket. I set the snoop utility to listen to port 1521 on my local machine, connecting to my primary server (see Figure 1).

Next I set my connection URL such that the primary connection would go through the Snoop listener on my local machine, so that closing the Snoop window effectively simulates a connection failure. Listing 1 shows what my URL looked like. (Listings 1 - 4 can be downloaded here.)

Note that the primary server is to my local machine (nc-jdavis), which goes through Snoop to nc-lnx08 (in the Snoop window). In the URL, I added my failover options to indicate that nc-linux02 is the alternate server and I want the option for failoverMode. Setting failoverMode=select indicates to the driver that I want to failover seamlessly while going through the data - in other words, I'm telling it: "Make it look like I never got disconnected." In addition, I set a small performance option, failoverPreConnect, that causes the driver to connect to both the primary and alternate server during the first connect. This saves my application from incurring the cost of connecting during the failover process. It isn't much, but at runtime every bit counts. Let's take a look at the code that displays the results:

while (results.next()){
for (int i=1; i <= numCols ; i++) {
System.out.print("'" + results.getString(i) + "'\t");
}
}

You'll notice immediately that this looks like a standard loop iterating through the results and printing them to the screen. How do I know that I've failed over successfully? Easy - I check the warnings object, which will indicate when the failover occurs (see Listing 2).

Why not show something that indicates the failover? Because I don't want to have to change my code to add failover on the client side; I want it to work with my middleware out of the box (that is, with no changes necessary to client code). In addition, if the application were being developed using a packaged application framework (think Hibernate or Cognos), then you cannot change application code, which makes using this failover mechanism easy to incorporate in any application architecture.

Now I run the application. Notice that the output is formatted for easy reading. In Listing 3 you can see the successful connection information for the server as well as the rows of golf course information.

You can see that I've successfully connected to the primary server and fetched all the data. So the application works. But this is not the purpose of the demo: I want to see it fail. I set a breakpoint (or code in a pause such as System.in) on the line in my application containing the System.out.println() statement, then debugged the application and, when I hit the breakpoint, continued through it for the first six rows. The Snoop window showed my connection (see Figure 2).

Next, I simply closed the window, effectively terminating my socket connection with the database and hanging it there. Continuing again, I see that row seven has nevertheless printed out. The driver caught the "connection failed" exception, connected to the alternate database (nc-lnx02), replayed the connection parameters, refetched, validated the data, and positioned on the correct row. The only indicator that anything happened is in the warnings object, indicating a successful failover. This can be logged to the application logs, or used as a trigger to send an e-mail to the systems administrator for action. Listing 4 shows the output when the failover happened.

The Right Database Connectivity Middleware Is Key
Putting the logic of failover in an application is tedious and expensive. As the sample provided here demonstrates, letting the middleware handle the failover and repositioning logic can be a better strategy in terms of saving development time and costs and focusing on satisfying the needs of your users. However, this recommendation comes with a caveat: not all database connectivity drivers have this capability or, having it, can deliver it with sufficient robustness to serve as a viable failover strategy.

Database drivers provided by the database vendor, for instance - and often used by systems architects as the default choice - provide limited if any application failover support. In such cases failover typically involves dependencies on proprietary high availability environments such as Oracle RAC, Microsoft Cluster Server (MSCS), or DB2 High Availability Disaster Recovery (HADR). Where failover support is provided, it is only in drivers that are based on client-side libraries. For Java that means Type 2 architecture - which, in turn, means inferior runtime performance and increased deployment and maintenance costs.

If you're considering the simplicity and flexibility of application failover provided by data connectivity middleware, look for high-quality drivers that provide the following important benefits:

  • No reliance on expensive and hard-to-implement server dependencies.
  • Failover managed entirely by the driver, simplifying application code.
  • Flexible and configurable failover options for various enterprise requirements.
  • Standards-based approach, to provide consistency regardless of environment.
  • Client load balancing, which works with failover to help distribute new connections so that no one server is overwhelmed with connection requests.

Making sure that application failover can handle connection failures in a standard way is key to ensuring the stability and uptime required by your customers. The database connectivity driver you implement should be an important part of your failover strategy. Some of them offer simple, cost-effective, yet sophisticated failover support to relational data sources, managed by the database driver versus adding costs in the application programs or implementing costly failover options provided by the database vendors. Obviously this is an offer you can't - or at least shouldn't - refuse to consider.

More Stories By Jesse Davis

Jesse Davis is the Senior Engineering Manager for Progress DataDirect Connect product line, and has more than 12 years experience developing database middleware, including JDBC and ODBC drivers, ADO.NET providers, and data services. Jesse is responsible for DataDirect’s Connect product development initiatives and forward looking research.

Comments (1) 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
MoonRainbow 11/19/09 07:39:00 PM EST

Unfortunately your solutions doesn't say anything about the genesis of data. How is the data gets propagated between primary and backup? Any failover solution must take this into account, because if you don't implement it correctly, your databases might not be accessible for quite a while after one crash. Opening simultaneous connections to both databases at start-up is also not a highly scalable approach, because you quickly use network and database resources that way.

@ThingsExpo Stories
The Internet of Things will greatly expand the opportunities for data collection and new business models driven off of that data. In her session at @ThingsExpo, Esmeralda Swartz, CMO of MetraTech, discussed how for this to be effective you not only need to have infrastructure and operational models capable of utilizing this new phenomenon, but increasingly service providers will need to convince a skeptical public to participate. Get ready to show them the money!
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.
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.
Connected devices and the Internet of Things are getting significant momentum in 2014. In his session at Internet of @ThingsExpo, Jim Hunter, Chief Scientist & Technology Evangelist at Greenwave Systems, examined three key elements that together will drive mass adoption of the IoT before the end of 2015. The first element is the recent advent of robust open source protocols (like AllJoyn and WebRTC) that facilitate M2M communication. The second is broad availability of flexible, cost-effective storage designed to handle the massive surge in back-end data in a world where timely analytics is e...
The Internet of Things will put IT to its ultimate test by creating infinite new opportunities to digitize products and services, generate and analyze new data to improve customer satisfaction, and discover new ways to gain a competitive advantage across nearly every industry. In order to help corporate business units to capitalize on the rapidly evolving IoT opportunities, IT must stand up to a new set of challenges. In his session at @ThingsExpo, Jeff Kaplan, Managing Director of THINKstrategies, will examine why IT must finally fulfill its role in support of its SBUs or face a new round of...
"There is a natural synchronization between the business models, the IoT is there to support ,” explained Brendan O'Brien, Co-founder and Chief Architect of Aria Systems, in this SYS-CON.tv interview at the 15th International Cloud Expo®, held Nov 4–6, 2014, at the Santa Clara Convention Center in Santa Clara, CA.
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.
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...

Building low-cost wearable devices can enhance the quality of our lives. In his session at Internet of @ThingsExpo, Sai Yamanoor, Embedded Software Engineer at Altschool, provided an example of putting together a small keychain within a $50 budget that educates the user about the air quality in their surroundings. He also provided examples such as building a wearable device that provides transit or recreational information. He then reviewed the resources available to build wearable devices at home including open source hardware, the raw materials required and the options available to power s...
“The age of the Internet of Things is upon us,” stated Thomas Svensson, senior vice-president and general manager EMEA, ThingWorx, “and working with forward-thinking companies, such as Elisa, enables us to deploy our leading technology so that customers can profit from complete, end-to-end solutions.” ThingWorx, a PTC® (Nasdaq: PTC) business and Internet of Things (IoT) platform provider, announced on Monday that Elisa, Finnish provider of mobile and fixed broadband subscriptions, will deploy ThingWorx® platform technology to enable a new Elisa IoT service in Finland and Estonia.
Advanced Persistent Threats (APTs) are increasing at an unprecedented rate. The threat landscape of today is drastically different than just a few years ago. Attacks are much more organized and sophisticated. They are harder to detect and even harder to anticipate. In the foreseeable future it's going to get a whole lot harder. Everything you know today will change. Keeping up with this changing landscape is already a daunting task. Your organization needs to use the latest tools, methods and expertise to guard against those threats. But will that be enough? In the foreseeable future attacks w...
From telemedicine to smart cars, digital homes and industrial monitoring, the explosive growth of IoT has created exciting new business opportunities for real time calls and messaging. In his session at @ThingsExpo, Ivelin Ivanov, CEO and Co-Founder of Telestax, shared some of the new revenue sources that IoT created for Restcomm – the open source telephony platform from Telestax. Ivelin Ivanov is a technology entrepreneur who founded Mobicents, an Open Source VoIP Platform, to help create, deploy, and manage applications integrating voice, video and data. He is the co-founder of TeleStax, a...
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...
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...
Disruptive macro trends in technology are impacting and dramatically changing the "art of the possible" relative to supply chain management practices through the innovative use of IoT, cloud, machine learning and Big Data to enable connected ecosystems of engagement. Enterprise informatics can now move beyond point solutions that merely monitor the past and implement integrated enterprise fabrics that enable end-to-end supply chain visibility to improve customer service delivery and optimize supplier management. Learn about enterprise architecture strategies for designing connected systems tha...
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...
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...
"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.
Things are being built upon cloud foundations to transform organizations. This CEO Power Panel at 15th Cloud Expo, moderated by Roger Strukhoff, Cloud Expo and @ThingsExpo conference chair, addressed the big issues involving these technologies and, more important, the results they will achieve. Rodney Rogers, chairman and CEO of Virtustream; Brendan O'Brien, co-founder of Aria Systems, Bart Copeland, president and CEO of ActiveState Software; Jim Cowie, chief scientist at Dyn; Dave Wagstaff, VP and chief architect at BSQUARE Corporation; Seth Proctor, CTO of NuoDB, Inc.; and Andris Gailitis, C...