Click here to close now.

Welcome!

MICROSERVICES Authors: Liz McMillan, Elizabeth White, Michael Kanasoot, Carmen Gonzalez, Dana Gardner

Related Topics: MICROSERVICES, XML

MICROSERVICES: Article

Long-Running Transactions in SOA

Transaction management in long running service based activities

Most organizations that have tried have been successful in implementing a pliable Service Oriented Architecture (SOA) paradigm. Analysts have come out with strategies to translate existing applications into SOA-compliant systems using a staggered approach. The rewards reaped come in the form of low-cost maintenance and agility in their business, along with reusable and self-contained services. But there are still challenges in this form of service-based architecture and solutions need to be devised.

One of the biggest hurdles has been coordinating technology-agnostic services into a single long-running unit of work that produces predictable results. The transactions running across multiple services over multiple domains need to be synchronized to maintain business integrity. Currently organizations depend on proprietary solutions to coordinate transactions for data consistency. This article will walk you through the definition of long-running transaction in SOA and its challenges then talk about the various approaches to resolving the issue while retaining the characteristics of a service-based architecture.

ACID Applications
Applications utilize multiple services across different modules or layers to serve a particular business need. For example, security authentication, service information, EIS information, updating services need to coordinate in a business unit termed a transaction thatcomprehends data consistency and business integrity in an organization.

Transactions are a set of operations that must be executed entirely or not at all. The fault-tolerance mechanism of managing transactions is to maintain the so-called ACID properties: A - Atomicity (all or none), C - Consistency (the resource must start and end in a consistent state), I - Isolation (make the transactions appear isolated from all the other operations) and D - Durability (once notified, the transaction will persist). ACID provides concurrency in operations and retains data integrity.

ACID properties are easier to implement on transactions that run only a short time because during a transaction the resources are held in a locked state. Transactions that run for a long time can't afford to lock up resources. Till date, an ACID transaction assumes closely coupled systems that aren't an SOA-mandated environment. So the ACID properties in a long-running activity need to be applied so that locking doesn't occur, or if it does, then the duration of the locking is as short as possible.

Long-Running Transactions in Service-Crowded Systems
To understand the concept of a long-running transaction, we need to look first into the various lifetimes of a transaction. A transaction lifetime can be defined as the minimum amount of time a transaction is kept open. This time period can be anywhere from a few seconds to several hours. A transaction with a short lifetime can begin and end in a matter of seconds, while a long-running transaction can be alive for minutes, hours, even days depending upon the underlying business requirements and implementation. Transactions with a short lifetime are easy to handle since the resources they use can be locked for the time required by maintaining the ACID properties. But the same strategy can't be applied to long-running transactions. Locking up resources for a long time can seriously hamper the application's performance bringing in unnecessary deadlock situations and long wait-times. Any transaction left in an open state for an indefinite amount of time qualifies as a long-running transaction.

The following scenarios make long-running transactions possible:

  1. A transaction with lots of database queries
  2. B2B transactions
  3. Batch processes
  4. Pseudo-Asynchronous activities within a transaction
In a long running transaction with multiple queries made to the database, the failure of any single query would result in a transaction failure that requires rolling back completely to the previously saved safe state of the database. The scenario might be across different data sources across different administrative domains.

Batch processes run for long periods of time, usually for hours. Regularly backing up sensitive data is an example. In most cases, batch processes only involve reading data and hence not many transactional issues are encountered. But in certain cases these long batch processes can include modifying the data. A failure during that operation would require an equally long rollback process.

Pseudo-asynchronous activities are used in concurrent activities but the transactions are resumed at some kind of notification. Such operations can be trivial to handle as the control is passed on completely and there is a complex or no way back to reach the sender once the activity is completed. This results in a complex scenario where an independent or intelligently handled rollback needs to be initiated on the source.

In a SOA each functionality is separated as a service. So, a certain application may use many services to provide a defined functionality. The principles of SOA define services as separate platform- and system-independent entities - each capable of functioning on their own, thus providing reusability and interoperability across disparate platforms.

A long-running transaction creates a number of problems in a SOA architecture. As long as a transaction is limited to a closed environment, catching faults or exceptions and triggering the appropriate rollback mechanism can easily be defined in the underlying application architecture. For example, a transaction involving a database as a resource would already have mechanisms defined in it to handle errors and do rollbacks. Even in a distributed database environment these things can be taken care of. Imagine the same situation in an open SOA scenario where each transactional query is executed on an altogether different platform or system. How a rollback would be implemented in such a case is just one of the immediate questions that comes to mind.

Let's consider a scenario where the transaction involves the participation of three different services - each performing a particular operation. Only if all three operations are successful would the transaction be deemed a success. Any other outcome would result in the transaction being marked as a failure. Then, if and when the transaction fails, appropriate recovery measures have to be implemented. And to top it off, we can lock a resource only for the time when the service local to the resource is operating.

Troubles Within
Let's look into the problems encountered with long-running transactions in SOA. They can be referred to as failure cases:

  1. The participation of multiple services results in multiple endpoints being invoked during one cycle of the transaction. Any of these services can be down at the instance when the transaction is in process.
  2. SOA boasts of loosely coupled systems. Maintaining transactions is only possible in closely coupled systems.
  3. The services involved can be based on any platform. Because of the disparity among the underlying implementation of the services, a context can't be deployed across the services to manage the transactions.
  4. The current status in the flow of the transaction can't be known at a given instance.
  5. Ifasynchronous services are involved in the transaction they can't be reached back, unless the service information is explicitly passed on.
  6. Resources can't be kept in a locked state for long periods of time. To free a resource once the service is done with it, it must release it. Doing this can cause a problem later on if the service fails and a rollback is issued throughout all the services.
  7. Alternate methods need to be devised to perform the appropriate recovery operations. In most cases these methods are either platform-specific or too dependent on the underlying business process.
Viable Methodologies
Any methodology that tries to implement transaction management for a long-running transaction scenario in a SOA needs to make sure to:
  1. Uniquely identify a transaction across the various participating services
  2. Guarantee that the data is delivered and the notifications are sent
  3. Some compensation must be provided in case something goes wrong during the transaction
  4. Errors in asynchronous services have to be addressed
Keeping these points in mind, the following are some ways to manage long-running transactions in SOA:
  1. A compensation methodology
  2. Transaction coordinator
Methodology 1: Compensation
In an ideal situation any changes done during a long-running transaction must be reverted back to the original content in case there's a failure somewhere else along the flow of the transaction. This is precisely what happens in a closed environment and is known as a rollback. In a SOA architecture, a situation might arise where a rollback isn't an option. In that case, instead of a rollback, compensation is provided. For example, in WS choreography, the self-reliant services pass control messages back and forth to notify the participating services of a rollback operation.

Compensation may be defined as the most logical change applied to the resource to maintain data consistency and integrity. How it's constructed depends on the governing business rules and underlying technical implementation of the services. In certain cases, compensation can include a rollback. In the example above, if the transaction fails at the third service (the transaction is uniquely identified by an id throughout its lifetime), we need to perform a compensatory operation at the previous service to negate the effect caused by the transaction. So, if the second service sent out an e-mail announcing that it has implemented the changes, a compensatory operation would be to send another e-mail announcing the failure of the transaction and that the changes have been undone. A synchronous process showcasing the scenario is illustrated in Figure 1.

But what if the services participating in the process are asynchronous, as one would expect in a long-running transaction? One way would be to save states and service information.

Methodology 2: Transaction Coordinator
A more appropriate solution would be to orchestrate the process using a transaction manager or process coordinator. Instead of inter-service communication, the services would be answerable to the coordinator, which in turn would handle all the transaction and compensation scenarios. Once again the transaction will be uniquely identified throughout the transaction cycle by an id. This would help the coordinator perform compensatory operations on the required set of data. The coordinator can manage the service information as well. This would solve any issues with asynchronous services. Figure 2 illustrates the coordinator service. This kind of methodology is used mostly in service orchestration-type applications and is a more centralized approach unlike methodology 1.

Case study - Money Transfer Scenario
Consider a money transfer scenario (Figure 4) where a complete transaction process involves five different services. All five services are separated by virtue of both system and the language of implementation.

The first service, the initiation service, is exposed to the client to pick up the user input. It validates the necessary input parameters and processes the transaction by sequentially executing the credit service and the debit service. Then the system notifies the stakeholder and the internal logs for auditing.

With no transaction context involved in this processing, the services are executed independently with no knowledge of the member service status. There's no way for the executed services to rollback and for specific reasons:

  1. Service status isn't shared
  2. Non-availability of co-ordination federation in the processing
  3. Compensation services for revoking the services
Let's take one of the approaches and bridge the gaps. The solution is to have a coordinator orchestrating though the services and managing the transaction context. The coordinator invariably stores the status of the services and maintains the transaction supporting the ACID properties.

The coordinator receives the input and generates an id to uniquely identify the transaction. An acknowledgement is sent to the initiation service as RECEIVED. The initiation service notifies the client about the start of the process and provides the unique transaction id. The client can use this transaction id to monitor and track the transaction. The initiation service is now ready to take further client input. The coordinator maintains a log to record each operation it performs. The log is created against the transaction id.

After generating the id for the transaction, the coordinator calls the external service of the bank, which accepts the money. This credit service takes the necessary input and starts updating the records in the database. Depending upon the style of the compensation, state information is saved before the update process initiates. Once the update takes place successfully, an acknowledgement to the coordinator is sent. (Figure 3)

The coordinator then logs the changes and proceeds to call the debit service. The debit service makes the necessary changes to the local database to reflect the debit. The debit process follows the same pattern as the credit process. On successful operation, a DEBITED acknowledgement is sent to the coordinator. The coordinator notifies each service involved of successful individual transactions at each step by means enacts the 2PC execution. When there's a failure, the coordinator runs the compensation service for each activity.

Conclusion
The long-running transaction is designed specifically for business interactions that take a long time. The intention is to tie the logical single business-to-business unit of work across heterogeneous domains. Each methodology depends on the architecture of the system and the existing assets in the organization. Technical analysts need to differentiate such special transaction in the SOA study and deal with them through special defined methodologies.

References
1.  William Cox. "Transactional Web Services."
http://dev2dev.bea.com/pub/a/2004/01/cox.html

2.  Pat Helland. "Why I hate the phrase Long running Transactions..."
http://blogs.msdn.com/pathelland/archive/2004/08/12/213552.aspx

3.  Wikipedia Atomic Transactions:
http://en.wikipedia.org/wiki/Atomic_transaction
Database Transactions:
http://en.wikipedia.org/wiki/Database_transaction
Two-phase commit protocol:
http://en.wikipedia.org/wiki/2-phase_commit
ACID properties:
http://en.wikipedia.org/wiki/ACID

More Stories By Anshuk Pal Chaudhari

The authors are interning and/or working as part of the Web Services COE (Center of Excellence) for Infosys Technologies, a global IT consulting firm, and have substantial experience in publishing papers, presenting papers at conferences, and defining standards for SOA and Web services. The Web Services COE specializes in SOA, Web services, and other related technologies.

More Stories By Bijoy Majumdar

Bijoy Majumdar is a member of the Web Services COE (Center of Excellence) for Infosys Technologies, a global IT consulting firm, and has substantial experience in publishing papers, presenting papers at conferences, and defining standards for SOA and Web services. Prior to Infosys, Bijoy Majumdar worked as an IT Analyst, and had been a member of the GE Center of Excellence (e-center) under the E-Business Practice of Tata Consultancy Services.

More Stories By Sunny Saxena

Sunny Saxena currently works with the Web Services Centre of Excellence in SETLabs, the technology research division at Infosys Technologies, India. His interests range from Web service security platforms to aspect-oriented development models.

Comments (0)

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.


@MicroservicesExpo Stories
SYS-CON Events announced today that Cisco, the worldwide leader in IT that transforms how people connect, communicate and collaborate, has been named “Gold 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 City, NY. Cisco makes amazing things happen by connecting the unconnected. Cisco has shaped the future of the Internet by becoming the worldwide leader in transforming how people connect, communicate and collaborat...
Hosted PaaS providers have given independent developers and startups huge advantages in efficiency and reduced time-to-market over their more process-bound counterparts in enterprises. Software frameworks are now available that allow enterprise IT departments to provide these same advantages for developers in their own organization. In his workshop session at DevOps Summit, Troy Topnik, ActiveState’s Technical Product Manager, will show how on-prem or cloud-hosted Private PaaS can enable organ...
SYS-CON Events announced today that Akana, formerly SOA Software, has been named “Bronze Sponsor” of SYS-CON's 16th International Cloud Expo® New York, which will take place June 9-11, 2015, at the Javits Center in New York City, NY. Akana’s comprehensive suite of API Management, API Security, Integrated SOA Governance, and Cloud Integration solutions helps businesses accelerate digital transformation by securely extending their reach across multiple channels – mobile, cloud and Internet of Thi...
Cloud computing is changing the way we look at IT costs, according to industry experts on a recent Cloud Luminary Fireside Chat panel discussion. Enterprise IT, traditionally viewed as a cost center, now plays a central role in the delivery of software-driven goods and services. Therefore, companies need to understand their cloud utilization and resulting costs in order to ensure profitability on their business offerings. Led by Bernard Golden, this fireside chat offers valuable insights on ho...
Exelon Corporation employs technology and process improvements to optimize their IT operations, manage a merger and acquisition transition, and to bring outsourced IT operations back in-house. To learn more about how this leading energy provider in the US, with a family of companies having $23.5 billion in annual revenue, accomplishes these goals we're joined by Jason Thomas, Manager of Service, Asset and Release Management at Exelon. The discussion is moderated by me, Dana Gardner, Principal A...
SYS-CON Events announced today that MangoApps 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., and the 17th International Cloud Expo®, which will take place on November 3–5, 2015, at the Santa Clara Convention Center in Santa Clara, CA. MangoApps provides private all-in-one social intranets allowing workers to securely collaborate from anywhere in the world and from any device. Social, mobile, and eas...
SYS-CON Events announced today that Solgenia 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, and the 17th International Cloud Expo®, which will take place on November 3–5, 2015, at the Santa Clara Convention Center in Santa Clara, CA. Solgenia is the global market leader in Cloud Collaboration and Cloud Infrastructure software solutions. Designed to “Bridge the Gap” between Personal and Professional S...
Modern Systems announced completion of a successful project with its new Rapid Program Modernization (eavRPMa"c) software. The eavRPMa"c technology architecturally transforms legacy applications, enabling faster feature development and reducing time-to-market for critical software updates. Working with Modern Systems, the University of California at Santa Barbara (UCSB) leveraged eavRPMa"c to transform its Student Information System from Software AG's Natural syntax to a modern application lev...
SYS-CON Events announced today Sematext Group, Inc., a Brooklyn-based Performance Monitoring and Log Management solution provider, will exhibit at SYS-CON's DevOps Summit 2015 New York, which will take place on June 9-11, 2015, at the Javits Center in New York City, NY. Sematext is a globally distributed organization that builds innovative Cloud and On Premises solutions for performance monitoring, alerting and anomaly detection (SPM), log management and analytics (Logsene), search analytics (S...
In the midst of the widespread popularity and adoption of cloud computing, it seems like everything is being offered “as a Service” these days: Infrastructure? Check. Platform? You bet. Software? Absolutely. Toaster? It’s only a matter of time. With service providers positioning vastly differing offerings under a generic “cloud” umbrella, it’s all too easy to get confused about what’s actually being offered. In his session at 16th Cloud Expo, Kevin Hazard, Director of Digital Content for SoftL...
When it comes to microservices there are myths and uncertainty about the journey ahead. Deploying a “Hello World” app on Docker is a long way from making microservices work in real enterprises with large applications, complex environments and existing organizational structures. February 19, 2015 10:00am PT / 1:00pm ET → 45 Minutes Join our four experts: Special host Gene Kim, Gary Gruver, Randy Shoup and XebiaLabs’ Andrew Phillips as they explore the realities of microservices in today’s IT worl...
The world's leading Cloud event, Cloud Expo has launched Microservices Journal on the SYS-CON.com portal, featuring over 19,000 original articles, news stories, features, and blog entries. DevOps Journal is focused on this critical enterprise IT topic in the world of cloud computing. Microservices Journal offers top articles, news stories, and blog posts from the world's well-known experts and guarantees better exposure for its authors than any other publication. Follow new article posts on T...
SYS-CON Media announced that IBM, which offers the world’s deepest portfolio of technologies and expertise that are transforming the future of work, has launched ad campaigns on SYS-CON’s numerous online magazines such as Cloud Computing Journal, Virtualization Journal, SOA World Magazine, and IoT Journal. IBM’s campaigns focus on vendors in the technology marketplace, the future of testing, Big Data and analytics, and mobile platforms.
For those of us that have been practicing SOA for over a decade, it's surprising that there's so much interest in microservices. In fairness microservices don't look like the vendor play that was early SOA in the early noughties. But experienced SOA practitioners everywhere will be wondering if microservices is actually a good thing. You see microservices is basically an SOA pattern that inherits all the well-known SOA principles and adds characteristics that address the use of SOA for distribut...
Microservice architectures are the new hotness, even though they aren't really all that different (in principle) from the paradigm described by SOA (which is dead, or not dead, depending on whom you ask). One of the things this decompositional approach to application architecture does is encourage developers and operations (some might even say DevOps) to re-evaluate scaling strategies. In particular, the notion is forwarded that an application should be built to scale and then infrastructure sho...
SYS-CON Events announced today the IoT Bootcamp – Jumpstart Your IoT Strategy, being held June 9–10, 2015, in conjunction with 16th Cloud Expo and Internet of @ThingsExpo at the Javits Center in New York City. This is your chance to jumpstart your IoT strategy. Combined with real-world scenarios and use cases, the IoT Bootcamp is not just based on presentations but includes hands-on demos and walkthroughs. We will introduce you to a variety of Do-It-Yourself IoT platforms including Arduino, Ras...
Microservices are the result of decomposing applications. That may sound a lot like SOA, but SOA was based on an object-oriented (noun) premise; that is, services were built around an object - like a customer - with all the necessary operations (functions) that go along with it. SOA was also founded on a variety of standards (most of them coming out of OASIS) like SOAP, WSDL, XML and UDDI. Microservices have no standards (at least none deriving from a standards body or organization) and can be b...
Our guest on the podcast this week is Jason Bloomberg, President at Intellyx. When we build services we want them to be lightweight, stateless and scalable while doing one thing really well. In today's cloud world, we're revisiting what to takes to make a good service in the first place. Listen in to learn why following "the book" doesn't necessarily mean that you're solving key business problems.
Right off the bat, Newman advises that we should "think of microservices as a specific approach for SOA in the same way that XP or Scrum are specific approaches for Agile Software development". These analogies are very interesting because my expectation was that microservices is a pattern. So I might infer that microservices is a set of process techniques as opposed to an architectural approach. Yet in the book, Newman clearly includes some elements of concept model and architecture as well as p...
Microservices, for the uninitiated, are essentially the decomposition of applications into multiple services. This decomposition is often based on functional lines, with related functions being grouped together into a service. While this may sound a like SOA, it really isn't, especially given that SOA was an object-centered methodology that focused on creating services around "nouns" like customer and product. Microservices, while certainly capable of being noun-based, are just as likely to be v...