Click here to close now.

Welcome!

JAVA IoT Authors: JP Morgenthal, Pat Romanski, John Wetherill, Ruxit Blog, Liz McMillan

Related Topics: JAVA IoT

JAVA IoT: 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!
SYS-CON Events announced today that MetraTech, now part of Ericsson, 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. Ericsson is the driving force behind the Networked Society- a world leader in communications infrastructure, software and services. Some 40% of the world’s mobile traffic runs through networks Ericsson has supplied, serving more than 2.5 billion subscribers.
The Internet of Things is not only adding billions of sensors and billions of terabytes to the Internet. It is also forcing a fundamental change in the way we envision Information Technology. For the first time, more data is being created by devices at the edge of the Internet rather than from centralized systems. What does this mean for today's IT professional? In this Power Panel at @ThingsExpo, moderated by Conference Chair Roger Strukhoff, panelists will addresses this very serious issue of profound change in the industry.
SYS-CON Events announced today that BMC 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. BMC delivers software solutions that help IT transform digital enterprises for the ultimate competitive business advantage. BMC has worked with thousands of leading companies to create and deliver powerful IT management services. From mainframe to cloud to mobile, BMC pairs high-speed digital innovation with robust IT industrialization – allowing customers to provide amazing user experiences with optimized IT per...
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...
The world is at a tipping point where the technology, the device and global adoption are converging to such a point that we will see an explosion of a world where smartphone devices not only allow us to talk to each other, but allow for communication between everything – serving as a central hub from which we control our world – MediaTek is at the heart of both driving this and allowing the markets to drive this reality forward themselves. The next wave of consumer gadgets is here – smart, connected, and small. If your ambitions are big, so are ours. In his session at @ThingsExpo, Jack Hu, D...
SYS-CON Events announced today that DragonGlass, an enterprise search platform, 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. After eleven years of designing and building custom applications, OpenCrowd has launched DragonGlass, a cloud-based platform that enables the development of search-based applications. These are a new breed of applications that utilize a search index as their backbone for data retrieval. They can easily adapt to new data sets and provide access to both structured and unstruc...
The 4th International Internet of @ThingsExpo, co-located with the 17th International Cloud Expo - to be held November 3-5, 2015, at the Santa Clara Convention Center in Santa Clara, CA - announces that its Call for Papers is open. The Internet of Things (IoT) is the biggest idea since the creation of the Worldwide Web more than 20 years ago.
We’re entering a new era of computing technology that many are calling the Internet of Things (IoT). Machine to machine, machine to infrastructure, machine to environment, the Internet of Everything, the Internet of Intelligent Things, intelligent systems – call it what you want, but it’s happening, and its potential is huge. IoT is comprised of smart machines interacting and communicating with other machines, objects, environments and infrastructures. As a result, huge volumes of data are being generated, and that data is being processed into useful actions that can “command and control” thi...
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 ...
All major researchers estimate there will be tens of billions devices - computers, smartphones, tablets, and sensors - connected to the Internet by 2020. This number will continue to grow at a rapid pace for the next several decades. With major technology companies and startups seriously embracing IoT strategies, now is the perfect time to attend @ThingsExpo, June 9-11, 2015, at the Javits Center in New York City. Learn what is going on, contribute to the discussions, and ensure that your enterprise is as "IoT-Ready" as it can be
WebRTC defines no default signaling protocol, causing fragmentation between WebRTC silos. SIP and XMPP provide possibilities, but come with considerable complexity and are not designed for use in a web environment. In his session at @ThingsExpo, Matthew Hodgson, technical co-founder of the Matrix.org, discussed how Matrix is a new non-profit Open Source Project that defines both a new HTTP-based standard for VoIP & IM signaling and provides reference implementations.
Buzzword alert: Microservices and IoT at a DevOps conference? What could possibly go wrong? In this Power Panel at DevOps Summit, moderated by Jason Bloomberg, the leading expert on architecting agility for the enterprise and president of Intellyx, panelists will peel away the buzz and discuss the important architectural principles behind implementing IoT solutions for the enterprise. As remote IoT devices and sensors become increasingly intelligent, they become part of our distributed cloud environment, and we must architect and code accordingly. At the very least, you'll have no problem fil...
"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.
Almost everyone sees the potential of Internet of Things but how can businesses truly unlock that potential. The key will be in the ability to discover business insight in the midst of an ocean of Big Data generated from billions of embedded devices via Systems of Discover. Businesses will also need to ensure that they can sustain that insight by leveraging the cloud for global reach, scale and elasticity.
In their session at @ThingsExpo, Shyam Varan Nath, Principal Architect at GE, and Ibrahim Gokcen, who leads GE's advanced IoT analytics, focused on the Internet of Things / Industrial Internet and how to make it operational for business end-users. Learn about the challenges posed by machine and sensor data and how to marry it with enterprise data. They also discussed the tips and tricks to provide the Industrial Internet as an end-user consumable service using Big Data Analytics and Industrial Cloud.
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...
How do APIs and IoT relate? The answer is not as simple as merely adding an API on top of a dumb device, but rather about understanding the architectural patterns for implementing an IoT fabric. There are typically two or three trends: Exposing the device to a management framework Exposing that management framework to a business centric logic Exposing that business layer and data to end users. This last trend is the IoT stack, which involves a new shift in the separation of what stuff happens, where data lives and where the interface lies. For instance, it's a mix of architectural styles ...
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...
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...