Welcome!

Containers Expo Blog Authors: JP Morgenthal, Reinhard Brandstädter, Elizabeth White, Flint Brenton, Stefan Dietrich

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
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, will discuss how leveraging the Industrial Interne...
The increasing popularity of the Internet of Things necessitates that our physical and cognitive relationship with wearable technology will change rapidly in the near future. This advent means logging has become a thing of the past. Before, it was on us to track our own data, but now that data is automatically available. What does this mean for mHealth and the "connected" body? In her session at @ThingsExpo, Lisa Calkins, CEO and co-founder of Amadeus Consulting, will discuss the impact of wea...
Whether your IoT service is connecting cars, homes, appliances, wearable, cameras or other devices, one question hangs in the balance – how do you actually make money from this service? The ability to turn your IoT service into profit requires the ability to create a monetization strategy that is flexible, scalable and working for you in real-time. It must be a transparent, smoothly implemented strategy that all stakeholders – from customers to the board – will be able to understand and comprehe...
Increasing IoT connectivity is forcing enterprises to find elegant solutions to organize and visualize all incoming data from these connected devices with re-configurable dashboard widgets to effectively allow rapid decision-making for everything from immediate actions in tactical situations to strategic analysis and reporting. In his session at 18th Cloud Expo, Shikhir Singh, Senior Developer Relations Manager at Sencha, will discuss how to create HTML5 dashboards that interact with IoT devic...
In his session at @ThingsExpo, Chris Klein, CEO and Co-founder of Rachio, will discuss next generation communities that are using IoT to create more sustainable, intelligent communities. One example is Sterling Ranch, a 10,000 home development that – with the help of Siemens – will integrate IoT technology into the community to provide residents with energy and water savings as well as intelligent security. Everything from stop lights to sprinkler systems to building infrastructures will run ef...
Artificial Intelligence has the potential to massively disrupt IoT. In his session at 18th Cloud Expo, AJ Abdallat, CEO of Beyond AI, will discuss what the five main drivers are in Artificial Intelligence that could shape the future of the Internet of Things. AJ Abdallat is CEO of Beyond AI. He has over 20 years of management experience in the fields of artificial intelligence, sensors, instruments, devices and software for telecommunications, life sciences, environmental monitoring, process...
The demand for organizations to expand their infrastructure to multiple IT environments like the cloud, on-premise, mobile, bring your own device (BYOD) and the Internet of Things (IoT) continues to grow. As this hybrid infrastructure increases, the challenge to monitor the security of these systems increases in volume and complexity. In his session at 18th Cloud Expo, Stephen Coty, Chief Security Evangelist at Alert Logic, will show how properly configured and managed security architecture can...
We’ve worked with dozens of early adopters across numerous industries and will debunk common misperceptions, which starts with understanding that many of the connected products we’ll use over the next 5 years are already products, they’re just not yet connected. With an IoT product, time-in-market provides much more essential feedback than ever before. Innovation comes from what you do with the data that the connected product provides in order to enhance the customer experience and optimize busi...
A critical component of any IoT project is the back-end systems that capture data from remote IoT devices and structure it in a way to answer useful questions. Traditional data warehouse and analytical systems are mature technologies that can be used to handle large data sets, but they are not well suited to many IoT-scale products and the need for real-time insights. At Fuze, we have developed a backend platform as part of our mobility-oriented cloud service that uses Big Data-based approache...
SYS-CON Events announced today that Ericsson has been named “Gold Sponsor” of SYS-CON's @ThingsExpo, which will take place on June 7-9, 2016, at the Javits Center in New York, New York. Ericsson is a world leader in the rapidly changing environment of communications technology – providing equipment, software and services to enable transformation through mobility. Some 40 percent of global mobile traffic runs through networks we have supplied. More than 1 billion subscribers around the world re...
SYS-CON Events announced today that Peak 10, Inc., a national IT infrastructure and cloud services provider, will exhibit at SYS-CON's 18th International Cloud Expo®, which will take place on June 7-9, 2016, at the Javits Center in New York City, NY. Peak 10 provides reliable, tailored data center and network services, cloud and managed services. Its solutions are designed to scale and adapt to customers’ changing business needs, enabling them to lower costs, improve performance and focus inter...
The IoTs 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, will demonstrate how to move beyond today's coding paradigm and share the must-have mindsets for removing complexity from the development proc...
We're entering the post-smartphone era, where wearable gadgets from watches and fitness bands to glasses and health aids will power the next technological revolution. With mass adoption of wearable devices comes a new data ecosystem that must be protected. Wearables open new pathways that facilitate the tracking, sharing and storing of consumers’ personal health, location and daily activity data. Consumers have some idea of the data these devices capture, but most don’t realize how revealing and...
trust and privacy in their ecosystem. Assurance and protection of device identity, secure data encryption and authentication are the key security challenges organizations are trying to address when integrating IoT devices. This holds true for IoT applications in a wide range of industries, for example, healthcare, consumer devices, and manufacturing. In his session at @ThingsExpo, Lancen LaChance, vice president of product management, IoT solutions at GlobalSign, will teach IoT developers how t...
There is an ever-growing explosion of new devices that are connected to the Internet using “cloud” solutions. This rapid growth is creating a massive new demand for efficient access to data. And it’s not just about connecting to that data anymore. This new demand is bringing new issues and challenges and it is important for companies to scale for the coming growth. And with that scaling comes the need for greater security, gathering and data analysis, storage, connectivity and, of course, the...
So, you bought into the current machine learning craze and went on to collect millions/billions of records from this promising new data source. Now, what do you do with them? Too often, the abundance of data quickly turns into an abundance of problems. How do you extract that "magic essence" from your data without falling into the common pitfalls? In her session at @ThingsExpo, Natalia Ponomareva, Software Engineer at Google, will provide tips on how to be successful in large scale machine lear...
Digital payments using wearable devices such as smart watches, fitness trackers, and payment wristbands are an increasing area of focus for industry participants, and consumer acceptance from early trials and deployments has encouraged some of the biggest names in technology and banking to continue their push to drive growth in this nascent market. Wearable payment systems may utilize near field communication (NFC), radio frequency identification (RFID), or quick response (QR) codes and barcodes...
You think you know what’s in your data. But do you? Most organizations are now aware of the business intelligence represented by their data. Data science stands to take this to a level you never thought of – literally. The techniques of data science, when used with the capabilities of Big Data technologies, can make connections you had not yet imagined, helping you discover new insights and ask new questions of your data. In his session at @ThingsExpo, Sarbjit Sarkaria, data science team lead ...
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, will explain how M2M certificates can efficiently enable confidentiality, integrity, and authenticity on highly constrained devices.
You deployed your app with the Bluemix PaaS and it's gaining some serious traction, so it's time to make some tweaks. Did you design your application in a way that it can scale in the cloud? Were you even thinking about the cloud when you built the app? If not, chances are your app is going to break. Check out this webcast to learn various techniques for designing applications that will scale successfully in Bluemix, for the confidence you need to take your apps to the next level and beyond.