Welcome!

@CloudExpo Authors: Elizabeth White, Kelly Burford, Karthick Viswanathan, Xenia von Wedel, Yeshim Deniz

Related Topics: Microservices Expo

Microservices Expo: Article

Is SOA Non-Trivial?

Exploring key service characteristics

Contract Based
Software in general is required to conform to a defined functional interface, and services are no different in this respect. For example, web service interfaces defined in WSDL (Web Service Definition Language) allow the definition of data types, input and output messages, operations, invocation protocols, and even the location of services. WS-Policy may also be used to define additional elements of the interface such as security policies.

Interfaces are however very weak on the behavioural aspects (semantics) of services. A service could return structurally correct data to a consumer but still not meet its functional obligations. Ensuring that services satisfy the behavioural contract is best done through automated test suites in my experience. Perhaps one day we will be able to define pre- and post-conditions and have these verified by the service management software, but don't hold your breath.

In addition to functional obligations, services also have operational obligations both to their consumers and to their operators. In other words service contracts are much more like SLAs and OLAs than traditional functional interfaces.

Contracts should ideally be kept in the service registry/repository, and where possible in a machine readable format to be used by service management software to help enforce the contracts at runtime.  Of course such runtime enforcement of contracts comes with a necessary performance penalty, but lets not spoil a lovely ideal with picky details... ;-)

Composable
Composability is the ability of services to be used in orchestration scenarios by higher level services or processes. It is a special case of the reusability characteristic in that the services need to be uniform as well as reusable. The primary reason for this requirement is that the orchestrating service will in all probability be built using something like BPEL, not a conventional programming language, so any variations in service style become more difficult to deal with.

This uniformity includes things like:

1. Interface Granularity
I hate the phrase "coarse-grained" because it's almost meaningless in any practical sense; however, services do need to ideally offer a uniform level of granularity in order to be composable.

2. Error Handling
Service consumers need to be able to differentiate between unexpected and generally unmanageable "system" exceptions, and recoverable "business" exceptions that may be retried under different conditions or by supplying different data. In the case of system exceptions, the consumer won't know for sure if the service operation completed or not, since, for example, the network connection might have died after the service completed its transaction. For this reason it is desirable that services be idempotent, i.e., retry-able. Where services are not idempotent, compensating (undo) operations should be offered.

3. Security
Composable services should ideally offer a uniform security model to consumers, including single sign-on abilities, channel or payload encryption.

While it is possible to design such uniformity into your services, the reality is that in a typical enterprise landscape the underlying service platforms and functional interfaces will be quite varied. This is where Enterprise Service Buses come in, providing features such as multi-channel adapters, single sign-on, security adapters, routing, message transformation, as well as world peace (if you believe the vendors.)

Abstract
Services must be abstract in the sense that they offer a functional interface that is not tied to any particular underlying implementation of that interface. In other words they should hide implementation details such as programming language, operating system platform, database structure, internal object model, etc. Abstraction supports other service characteristics such as reusability, extensibility, as well as reduces coupling between producer and consumer.

The degree of service abstraction that is achieved is often linked to whether the service was designed top down or bottom up.

Top-down services begin with a business domain model and processes that ultimately translate to service operations and types, e.g., in the form of WSDL and XML Schema, in the case of web services. Such services will offer the highest level of abstraction since they are designed without an implementation in mind. However, top-down services require a translation between the interface and implementation that can sometimes introduce a performance penalty, e.g., translating business keys to database identifiers.

Bottom-up services begin with an implementation and typically involve the use of toolkits to generate the service interfaces. Such services are closely coupled to their implementations and consumers. However, bottom-up services are enticing because first they offer the ability to quickly expose existing code as services, and second because they allow the use of implementation specifics such as database identifiers to improve performance.

These gains offer a false economy and should be strenuously resisted. The long-term gains of well-designed, adaptable services that reflect a business domain far outweigh any short-term performance or time-to-market gains.

Autonomous
A service is autonomous if it has full control over its internal logic. This requires that it has clearly defined and isolated (decoupled) functional and operational boundaries, that it is independent of other services, and that it only communicates via contract-driven messages and policies.

A consumer should exercise no influence over the service other than to execute it and provide input values. The service should have minimal dependency on its execution environment.

Autonomy has benefits for both the service consumer and provider:

  • Consumers are protected in that the service adheres strictly to agreed contracts.
  • Providers have greater reassurance because service-level agreements are adhered to and services offer deployment flexibility because of their environment independence

Extensible
The only constant in life is change, and this is no different for services. Services must be built with this fact in mind: that they will have to adapt to new or changing requirements. Extensibility is the ability of services to adapt while preserving existing consumer contracts.

We would expect the following types of changes to services to have no impact on other consumers:

1. Internal Source Code Changes
Insulating consumers from internal changes is achieved through another service characteristic: abstraction, i.e., it is critical that services do not "leak" implementation details into the interface. A typical example of this is the use of underlying database identifiers in the interface instead of meaningful business keys.

2. Interface Extensions
In general, interface changes will break existing code. The exceptions to this are the addition of new operations or certain types of service data extension. Where breaking changes are introduced, a versioning scheme is required to separate the old and the new, while supporting both concurrently. Versioning for web services is typically done via the introduction of major and minor numbers to XML namespaces, such as proposed <a href="http://blogs.iona.com/sos/20070410-WSDL-Versioning-Best-Practise.pdf">here</a>, or alternatively via a service lookup registry.

3. New Consumer Take-on
The take-on of new consumers will increase the load on a service. Services need to ensure that previously agreed consumer service-level agreements (SLA) are not violated. Achieving this will involve a combination of automated performance regression test suites and runtime SLA monitoring.

4. Environmental changes
Services need to ensure that any planned maintenance that is performed on their underlying execution platform such as the application of critical patches does not affect consumers. Services need to run in a cluster with the ability for service instances to be transparently taken out of commission during maintenance periods while other service instances continue to support consumer requests. It is advisable to run automated regression test suites after such maintenance.

More Stories By Robert Morschel

Robert Morschel is chief architect at Neptune Software Plc and has extensive experience in distributed software development for companies such as British Telecom, Nomura and Fidelity Investments. He blogs on SOA at soaprobe.blogspot.com.

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.


@CloudExpo Stories
Leading companies, from the Global Fortune 500 to the smallest companies, are adopting hybrid cloud as the path to business advantage. Hybrid cloud depends on cloud services and on-premises infrastructure working in unison. Successful implementations require new levels of data mobility, enabled by an automated and seamless flow across on-premises and cloud resources. In his general session at 21st Cloud Expo, Greg Tevis, an IBM Storage Software Technical Strategist and Customer Solution Architec...
The cloud era has reached the stage where it is no longer a question of whether a company should migrate, but when. Enterprises have embraced the outsourcing of where their various applications are stored and who manages them, saving significant investment along the way. Plus, the cloud has become a defining competitive edge. Companies that fail to successfully adapt risk failure. The media, of course, continues to extol the virtues of the cloud, including how easy it is to get there. Migrating...
In his keynote at 18th Cloud Expo, Andrew Keys, Co-Founder of ConsenSys Enterprise, provided an overview of the evolution of the Internet and the Database and the future of their combination – the Blockchain. Andrew Keys is Co-Founder of ConsenSys Enterprise. He comes to ConsenSys Enterprise with capital markets, technology and entrepreneurial experience. Previously, he worked for UBS investment bank in equities analysis. Later, he was responsible for the creation and distribution of life settle...
The use of containers by developers -- and now increasingly IT operators -- has grown from infatuation to deep and abiding love. But as with any long-term affair, the honeymoon soon leads to needing to live well together ... and maybe even getting some relationship help along the way. And so it goes with container orchestration and automation solutions, which are rapidly emerging as the means to maintain the bliss between rapid container adoption and broad container use among multiple cloud host...
Blockchain is a shared, secure record of exchange that establishes trust, accountability and transparency across business networks. Supported by the Linux Foundation's open source, open-standards based Hyperledger Project, Blockchain has the potential to improve regulatory compliance, reduce cost as well as advance trade. Are you curious about how Blockchain is built for business? In her session at 21st Cloud Expo, René Bostic, Technical VP of the IBM Cloud Unit in North America, discussed the b...
Blockchain. A day doesn’t seem to go by without seeing articles and discussions about the technology. According to PwC executive Seamus Cushley, approximately $1.4B has been invested in blockchain just last year. In Gartner’s recent hype cycle for emerging technologies, blockchain is approaching the peak. It is considered by Gartner as one of the ‘Key platform-enabling technologies to track.’ While there is a lot of ‘hype vs reality’ discussions going on, there is no arguing that blockchain is b...
Imagine if you will, a retail floor so densely packed with sensors that they can pick up the movements of insects scurrying across a store aisle. Or a component of a piece of factory equipment so well-instrumented that its digital twin provides resolution down to the micrometer.
"IBM is really all in on blockchain. We take a look at sort of the history of blockchain ledger technologies. It started out with bitcoin, Ethereum, and IBM evaluated these particular blockchain technologies and found they were anonymous and permissionless and that many companies were looking for permissioned blockchain," stated René Bostic, Technical VP of the IBM Cloud Unit in North America, in this SYS-CON.tv interview at 21st Cloud Expo, held Oct 31 – Nov 2, 2017, at the Santa Clara Conventi...
While some developers care passionately about how data centers and clouds are architected, for most, it is only the end result that matters. To the majority of companies, technology exists to solve a business problem, and only delivers value when it is solving that problem. 2017 brings the mainstream adoption of containers for production workloads. In his session at 21st Cloud Expo, Ben McCormack, VP of Operations at Evernote, discussed how data centers of the future will be managed, how the p...
As DevOps methodologies expand their reach across the enterprise, organizations face the daunting challenge of adapting related cloud strategies to ensure optimal alignment, from managing complexity to ensuring proper governance. How can culture, automation, legacy apps and even budget be reexamined to enable this ongoing shift within the modern software factory? In her Day 2 Keynote at @DevOpsSummit at 21st Cloud Expo, Aruna Ravichandran, VP, DevOps Solutions Marketing, CA Technologies, was jo...
"Since we launched LinuxONE we learned a lot from our customers. More than anything what they responded to were some very unique security capabilities that we have," explained Mark Figley, Director of LinuxONE Offerings at IBM, in this SYS-CON.tv interview at 21st Cloud Expo, held Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA.
When shopping for a new data processing platform for IoT solutions, many development teams want to be able to test-drive options before making a choice. Yet when evaluating an IoT solution, it’s simply not feasible to do so at scale with physical devices. Building a sensor simulator is the next best choice; however, generating a realistic simulation at very high TPS with ease of configurability is a formidable challenge. When dealing with multiple application or transport protocols, you would be...
Nordstrom is transforming the way that they do business and the cloud is the key to enabling speed and hyper personalized customer experiences. In his session at 21st Cloud Expo, Ken Schow, VP of Engineering at Nordstrom, discussed some of the key learnings and common pitfalls of large enterprises moving to the cloud. This includes strategies around choosing a cloud provider(s), architecture, and lessons learned. In addition, he covered some of the best practices for structured team migration an...
In his session at 21st Cloud Expo, Raju Shreewastava, founder of Big Data Trunk, provided a fun and simple way to introduce Machine Leaning to anyone and everyone. He solved a machine learning problem and demonstrated an easy way to be able to do machine learning without even coding. Raju Shreewastava is the founder of Big Data Trunk (www.BigDataTrunk.com), a Big Data Training and consulting firm with offices in the United States. He previously led the data warehouse/business intelligence and B...
Smart cities have the potential to change our lives at so many levels for citizens: less pollution, reduced parking obstacles, better health, education and more energy savings. Real-time data streaming and the Internet of Things (IoT) possess the power to turn this vision into a reality. However, most organizations today are building their data infrastructure to focus solely on addressing immediate business needs vs. a platform capable of quickly adapting emerging technologies to address future ...
In his general session at 21st Cloud Expo, Greg Dumas, Calligo’s Vice President and G.M. of US operations, discussed the new Global Data Protection Regulation and how Calligo can help business stay compliant in digitally globalized world. Greg Dumas is Calligo's Vice President and G.M. of US operations. Calligo is an established service provider that provides an innovative platform for trusted cloud solutions. Calligo’s customers are typically most concerned about GDPR compliance, application p...
You know you need the cloud, but you’re hesitant to simply dump everything at Amazon since you know that not all workloads are suitable for cloud. You know that you want the kind of ease of use and scalability that you get with public cloud, but your applications are architected in a way that makes the public cloud a non-starter. You’re looking at private cloud solutions based on hyperconverged infrastructure, but you’re concerned with the limits inherent in those technologies.
Is advanced scheduling in Kubernetes achievable?Yes, however, how do you properly accommodate every real-life scenario that a Kubernetes user might encounter? How do you leverage advanced scheduling techniques to shape and describe each scenario in easy-to-use rules and configurations? In his session at @DevOpsSummit at 21st Cloud Expo, Oleg Chunikhin, CTO at Kublr, answered these questions and demonstrated techniques for implementing advanced scheduling. For example, using spot instances and co...
DevOps is under attack because developers don’t want to mess with infrastructure. They will happily own their code into production, but want to use platforms instead of raw automation. That’s changing the landscape that we understand as DevOps with both architecture concepts (CloudNative) and process redefinition (SRE). Rob Hirschfeld’s recent work in Kubernetes operations has led to the conclusion that containers and related platforms have changed the way we should be thinking about DevOps and...
The need for greater agility and scalability necessitated the digital transformation in the form of following equation: monolithic to microservices to serverless architecture (FaaS). To keep up with the cut-throat competition, the organisations need to update their technology stack to make software development their differentiating factor. Thus microservices architecture emerged as a potential method to provide development teams with greater flexibility and other advantages, such as the abili...