Java IoT Authors: Yeshim Deniz, Carmen Gonzalez, Elizabeth White, Pat Romanski, Jim Kaskade

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
Why do your mobile transformations need to happen today? Mobile is the strategy that enterprise transformation centers on to drive customer engagement. In his general session at @ThingsExpo, Roger Woods, Director, Mobile Product & Strategy – Adobe Marketing Cloud, covered key IoT and mobile trends that are forcing mobile transformation, key components of a solid mobile strategy and explored how brands are effectively driving mobile change throughout the enterprise.
In past @ThingsExpo presentations, Joseph di Paolantonio has explored how various Internet of Things (IoT) and data management and analytics (DMA) solution spaces will come together as sensor analytics ecosystems. This year, in his session at @ThingsExpo, Joseph di Paolantonio from DataArchon, will be adding the numerous Transportation areas, from autonomous vehicles to “Uber for containers.” While IoT data in any one area of Transportation will have a huge impact in that area, combining senso...
"Matrix is an ambitious open standard and implementation that's set up to break down the fragmentation problems that exist in IP messaging and VoIP communication," explained John Woolf, Technical Evangelist at Matrix, in this SYS-CON.tv interview at @ThingsExpo, held Nov 4–6, 2014, at the Santa Clara Convention Center in Santa Clara, CA.
@ThingsExpo has been named the Top 5 Most Influential Internet of Things Brand by Onalytica in the ‘The Internet of Things Landscape 2015: Top 100 Individuals and Brands.' Onalytica analyzed Twitter conversations around the #IoT debate to uncover the most influential brands and individuals driving the conversation. Onalytica captured data from 56,224 users. The PageRank based methodology they use to extract influencers on a particular topic (tweets mentioning #InternetofThings or #IoT in this ...
The IoT has the potential to create a renaissance of manufacturing in the US and elsewhere. In his session at 18th Cloud Expo, Florent Solt, CTO and chief architect of Netvibes, discussed how the expected exponential increase in the amount of data that will be processed, transported, stored, and accessed means there will be a huge demand for smart technologies to deliver it. Florent Solt is the CTO and chief architect of Netvibes. Prior to joining Netvibes in 2007, he co-founded Rift Technologi...
For basic one-to-one voice or video calling solutions, WebRTC has proven to be a very powerful technology. Although WebRTC’s core functionality is to provide secure, real-time p2p media streaming, leveraging native platform features and server-side components brings up new communication capabilities for web and native mobile applications, allowing for advanced multi-user use cases such as video broadcasting, conferencing, and media recording.
24Notion is full-service global creative digital marketing, technology and lifestyle agency that combines strategic ideas with customized tactical execution. With a broad understand of the art of traditional marketing, new media, communications and social influence, 24Notion uniquely understands how to connect your brand strategy with the right consumer. 24Notion ranked #12 on Corporate Social Responsibility - Book of List.
Established in 1998, Calsoft is a leading software product engineering Services Company specializing in Storage, Networking, Virtualization and Cloud business verticals. Calsoft provides End-to-End Product Development, Quality Assurance Sustenance, Solution Engineering and Professional Services expertise to assist customers in achieving their product development and business goals. The company's deep domain knowledge of Storage, Virtualization, Networking and Cloud verticals helps in delivering ...
SYS-CON Events announced today that SoftNet Solutions 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. SoftNet Solutions specializes in Enterprise Solutions for Hadoop and Big Data. It offers customers the most open, robust, and value-conscious portfolio of solutions, services, and tools for the shortest route to success with Big Data. The unique differentiator is the ability to architect and...
More and more brands have jumped on the IoT bandwagon. We have an excess of wearables – activity trackers, smartwatches, smart glasses and sneakers, and more that track seemingly endless datapoints. However, most consumers have no idea what “IoT” means. Creating more wearables that track data shouldn't be the aim of brands; delivering meaningful, tangible relevance to their users should be. We're in a period in which the IoT pendulum is still swinging. Initially, it swung toward "smart for smar...
@ThingsExpo has been named the Top 5 Most Influential M2M Brand by Onalytica in the ‘Machine to Machine: Top 100 Influencers and Brands.' Onalytica analyzed the online debate on M2M by looking at over 85,000 tweets to provide the most influential individuals and brands that drive the discussion. According to Onalytica the "analysis showed a very engaged community with a lot of interactive tweets. The M2M discussion seems to be more fragmented and driven by some of the major brands present in the...
Cognitive Computing is becoming the foundation for a new generation of solutions that have the potential to transform business. Unlike traditional approaches to building solutions, a cognitive computing approach allows the data to help determine the way applications are designed. This contrasts with conventional software development that begins with defining logic based on the current way a business operates. In her session at 18th Cloud Expo, Judith S. Hurwitz, President and CEO of Hurwitz & ...
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...
In his keynote at 19th Cloud Expo, Sheng Liang, co-founder and CEO of Rancher Labs, will discuss the technological advances and new business opportunities created by the rapid adoption of containers. With the success of Amazon Web Services (AWS) and various open source technologies used to build private clouds, cloud computing has become an essential component of IT strategy. However, users continue to face challenges in implementing clouds, as older technologies evolve and newer ones like Docke...
As ridesharing competitors and enhanced services increase, notable changes are occurring in the transportation model. Despite the cost-effective means and flexibility of ridesharing, both drivers and users will need to be aware of the connected environment and how it will impact the ridesharing experience. In his session at @ThingsExpo, Timothy Evavold, Executive Director Automotive at Covisint, will discuss key challenges and solutions to powering a ride sharing and/or multimodal model in the a...
Just over a week ago I received a long and loud sustained applause for a presentation I delivered at this year’s Cloud Expo in Santa Clara. I was extremely pleased with the turnout and had some very good conversations with many of the attendees. Over the next few days I had many more meaningful conversations and was not only happy with the results but also learned a few new things. Here is everything I learned in those three days distilled into three short points.
SYS-CON Events announced today that Embotics, the cloud automation company, 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. Embotics is the cloud automation company for IT organizations and service providers that need to improve provisioning or enable self-service capabilities. With a relentless focus on delivering a premier user experience and unmatched customer support, Embotics is the fas...
SYS-CON Events announced today that Coalfire 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. Coalfire is the trusted leader in cybersecurity risk management and compliance services. Coalfire integrates advisory and technical assessments and recommendations to the corporate directors, executives, boards, and IT organizations for global brands and organizations in the technology, cloud, health...
The IoT industry is now at a crossroads, between the fast-paced innovation of technologies and the pending mass adoption by global enterprises. The complexity of combining rapidly evolving technologies and the need to establish practices for market acceleration pose a strong challenge to global enterprises as well as IoT vendors. In his session at @ThingsExpo, Clark Smith, senior product manager for Numerex, will discuss how Numerex, as an experienced, established IoT provider, has embraced a ...
Cloud based infrastructure deployment is becoming more and more appealing to customers, from Fortune 500 companies to SMEs due to its pay-as-you-go model. Enterprise storage vendors are able to reach out to these customers by integrating in cloud based deployments; this needs adaptability and interoperability of the products confirming to cloud standards such as OpenStack, CloudStack, or Azure. As compared to off the shelf commodity storage, enterprise storages by its reliability, high-availabil...