Welcome!

Microservices Expo Authors: Liz McMillan, Zakia Bouachraoui, Elizabeth White, Pat Romanski, Yeshim Deniz

Related Topics: Microservices Expo

Microservices Expo: News Item

Where Is the SOA in REST-Based SOA?

We must pare down the essentials of both REST and SOA to understand the true nature of the combined approach.

Over the years, updating our Licensed ZapThink Architect (LZA) course has given us ample time to explore advances in SOA and Cloud Computing. Now that we’re working on version 9 of the course, we’re taking a closer look at REST-based SOA. Of course, ZapThink has discussed REST for several years now, but recently we’ve seen some fascinating REST-based SOA case studies, both at startups as well as within the US Federal Government.

Nevertheless, while many architects believe that as an architectural style, REST is simpler and more straightforward that Web Services-based SOA, our research is turning up continued confusion over the principles of REST and how best to implement them. Everybody seems to get the basics—operate on resources at URIs with the four HTTP-centric operations GET, POST, PUT, and DELETE—but most people seem to miss the subtleties. Combine that confusion with the fact that you can do REST without SOA, the specifics of REST-based SOA are even more elusive, as we must pare down the essentials of both REST and SOA to understand the true nature of the combined approach. How, therefore, should we handle Service abstractions, contracts, and compositions – arguably, the essence of SOA – in a REST-based SOA world?

Where is the Service Abstraction?
At the center of the SOA approach is the notion of a Service abstraction. REST resources are abstractions as well, but resources are abstractions of capabilities or entities on the server, which is not quite the same thing as a Service abstraction. In SOA, the Service abstraction supports Business Services, which represent flexible, business-centric capabilities. A Business Service may abstract multiple Service interfaces, where routing and transformation operations on intermediaries present a loosely coupled façade.

Most RESTafarians, however, don’t think at this level. They are thinking of clients (e.g. browsers) accessing resources at URIs which return representations. A representation is an HTML page, an XML file, a video, etc. The business context is lost in a sea of URI formats and Internet media types.

What RESTafarians often overlook is that the intermediary pattern is actually one of the core architectural constraints of REST. URIs need not point directly to resources; it is perfectly OK for an intermediary to resolve the URI into a physical endpoint. After all, that’s what DNS servers do!

From the SOA perspective, we can rely upon the intermediary to execute routing rules and transformations as necessary to support the business abstraction. Furthermore, we can establish and enforce the policy (as a part of our SOA governance framework) that the only allowed way to access resources is via endpoints on an intermediary. From the REST perspective, think DNS server on steroids: instead of simply resolving URLs to IP addresses, resolve any formal URI structure to physical resource endpoints by following a rich set of transformation and routing metadata.

Where is the Contract?
At the technical level, a Service is a contracted interface or an abstraction of contracted interfaces. Web Services have contracts that comply with WSDL, but there’s no equivalent of WSDL for REST resources. True, resources have uniform interfaces that the four HTTP operations define, but simply knowing you can GET a resource or POST to a resource doesn’t tell you anything about what that resource is supposed to do. Accessing a resource does give you a representation of that resource, however. Representations can comply with standard Internet media types (formerly known as MIME types), but even the media type specification is insufficient to qualify as a contract.

Sun Microsystems tried to promote the Web Application Description Language (WADL) as a RESTafarian alternative to WSDL, but work on WADL has largely petered out now that Sun is part of Oracle. The point to WADL was more to stub out REST resources in Java than to provide an implementation-neutral contract language in any case.

Where, then, is the contract? Let’s look at a simple REST example: the simplest, of course, being the Web itself. Let’s say you are filling in a form on a Web page and then hit submit. Where is the contract?

The form method is POST, and the POST data are the information that you filled into the form. The resource is identified by the form action URL. So far so good. Have you found the contract yet?

In this example, the contract is the Web form itself. The form specifies and constrains the POST data you may input, and specifies the form action, which is a hyperlink to the next resource. You browsed to the page with the Web form by following an earlier link or loading a URL for a resource that returned that Web page as a representation of that resource.

Remember, a REST application is a set of resources that return representations that link to other resources – in other words, hypermedia. One resource returns one or more representations (Web pages, XML files, etc.) that contain links to other resources, and it is those hyperlinks (and their associated metadata) that specify the application behavior.

While a Web page with a form is the simplest and most common example of how to contract POST data, we can generalize that form however we like, depending on what type of client we want to support. For machine-to-machine interactions, for example (that is, when the client is not simply a browser), the first resource may return an XML representation that provides a contracted interface to the client for POSTing to the linked resource. How your resource builds that representation is up to you.

In Web Services-based SOA we store the contract metadata in a centralized registry/repository. In REST-based SOA each resource is responsible for returning contract metadata either for itself or for any resource it hyperlinks to. As a result, we may not able to obtain contracts for resources we’re not (yet) able to access, but on the other hand, we can code our resources to dynamically generate contracts if we wish. In REST-based SOA, therefore, contract changes can be automated, where in Web Services-based SOA, contract change is a complex, manual process that requires rigorous governance.

Where is the Composition?
The third core characteristic of SOA we look for is the ability to compose Services into applications. Such compositions might be orchestrations, when they have a pre-defined flow, or choreographies, when the order of steps in the composition is not determined ahead of time.

A REST application, of course, is an example of a composition of resources. From the SOA perspective, furthermore, a REST application is a workflow – that is, a composition with human steps. We can also consider such compositions to be choreographies, because the order of steps depends upon which links the user clicks. Users may click links in a different order every time they work their way through the application.

The question still remains: how do we create automated orchestrations in the REST world? The answer is simpler than it looks. In REST, everything can be a resource. Therefore, orchestrations can be resources as well. An orchestration resource might return a BPEL representation or a BPMN representation or perhaps a simplified representation of an orchestration that doesn’t have the baggage of either BPEL or BPMN. If anything, establishing a pre-defined orchestration is simpler than a hypermedia composition, because the orchestration logic is static, while with a hypermedia composition, the underlying resource logic may change the composition logic on the fly. Just because we don’t have to fix our application state transitions ahead of time doesn’t mean we’re not allowed to.

The ZapThink Take
Over the more than ten years ZapThink has been writing about SOA, we’ve fought the battle to explain what SOA really was, fighting the deluge of misinformation from profit-seeking vendors and ill-informed industry analysts. Fortunately, this time vendors aren’t trying to coopt REST to sell software the way they did SOA, to be sure, but the fact still remains that there is extensive confusion and misinformation about REST, just as there still is for SOA.

Mix the two together, therefore, and you’re just asking for trouble. But the effort is worth the trouble, for one simple fact: done right, REST-based SOA actually works. It paves a path to the agile architecture that we’ve been seeking since we first dipped our toe into the ocean of distributed computing. Of course, there’s a catch: the “done right” bit. The devil is in the details.

ZapThink will be providing far more detail on this topic over the next year, in our ZapFlash newsletters, in the next version of our LZA course, and in our Podcasts and at our events. Our new REST-based SOA module in the LZA course in particular breaks new ground and lays the groundwork for simpler, more successful approaches to SOA. Hope to see you at one of our events or classes soon!

More Stories By Jason Bloomberg

Jason Bloomberg is a leading IT industry analyst, Forbes contributor, keynote speaker, and globally recognized expert on multiple disruptive trends in enterprise technology and digital transformation. He is ranked #5 on Onalytica’s list of top Digital Transformation influencers for 2018 and #15 on Jax’s list of top DevOps influencers for 2017, the only person to appear on both lists.

As founder and president of Agile Digital Transformation analyst firm Intellyx, he advises, writes, and speaks on a diverse set of topics, including digital transformation, artificial intelligence, cloud computing, devops, big data/analytics, cybersecurity, blockchain/bitcoin/cryptocurrency, no-code/low-code platforms and tools, organizational transformation, internet of things, enterprise architecture, SD-WAN/SDX, mainframes, hybrid IT, and legacy transformation, among other topics.

Mr. Bloomberg’s articles in Forbes are often viewed by more than 100,000 readers. During his career, he has published over 1,200 articles (over 200 for Forbes alone), spoken at over 400 conferences and webinars, and he has been quoted in the press and blogosphere over 2,000 times.

Mr. Bloomberg is the author or coauthor of four books: The Agile Architecture Revolution (Wiley, 2013), Service Orient or Be Doomed! How Service Orientation Will Change Your Business (Wiley, 2006), XML and Web Services Unleashed (SAMS Publishing, 2002), and Web Page Scripting Techniques (Hayden Books, 1996). His next book, Agile Digital Transformation, is due within the next year.

At SOA-focused industry analyst firm ZapThink from 2001 to 2013, Mr. Bloomberg created and delivered the Licensed ZapThink Architect (LZA) Service-Oriented Architecture (SOA) course and associated credential, certifying over 1,700 professionals worldwide. He is one of the original Managing Partners of ZapThink LLC, which was acquired by Dovel Technologies in 2011.

Prior to ZapThink, Mr. Bloomberg built a diverse background in eBusiness technology management and industry analysis, including serving as a senior analyst in IDC’s eBusiness Advisory group, as well as holding eBusiness management positions at USWeb/CKS (later marchFIRST) and WaveBend Solutions (now Hitachi Consulting), and several software and web development positions.

Microservices Articles
The now mainstream platform changes stemming from the first Internet boom brought many changes but didn’t really change the basic relationship between servers and the applications running on them. In fact, that was sort of the point. In his session at 18th Cloud Expo, Gordon Haff, senior cloud strategy marketing and evangelism manager at Red Hat, will discuss how today’s workloads require a new model and a new platform for development and execution. The platform must handle a wide range of rec...
When building large, cloud-based applications that operate at a high scale, it’s important to maintain a high availability and resilience to failures. In order to do that, you must be tolerant of failures, even in light of failures in other areas of your application. “Fly two mistakes high” is an old adage in the radio control airplane hobby. It means, fly high enough so that if you make a mistake, you can continue flying with room to still make mistakes. In his session at 18th Cloud Expo, Lee A...
In his general session at 19th Cloud Expo, Manish Dixit, VP of Product and Engineering at Dice, discussed how Dice leverages data insights and tools to help both tech professionals and recruiters better understand how skills relate to each other and which skills are in high demand using interactive visualizations and salary indicator tools to maximize earning potential. Manish Dixit is VP of Product and Engineering at Dice. As the leader of the Product, Engineering and Data Sciences team at D...
Lori MacVittie is a subject matter expert on emerging technology responsible for outbound evangelism across F5's entire product suite. MacVittie has extensive development and technical architecture experience in both high-tech and enterprise organizations, in addition to network and systems administration expertise. Prior to joining F5, MacVittie was an award-winning technology editor at Network Computing Magazine where she evaluated and tested application-focused technologies including app secu...
Containers and Kubernetes allow for code portability across on-premise VMs, bare metal, or multiple cloud provider environments. Yet, despite this portability promise, developers may include configuration and application definitions that constrain or even eliminate application portability. In this session we'll describe best practices for "configuration as code" in a Kubernetes environment. We will demonstrate how a properly constructed containerized app can be deployed to both Amazon and Azure ...
Modern software design has fundamentally changed how we manage applications, causing many to turn to containers as the new virtual machine for resource management. As container adoption grows beyond stateless applications to stateful workloads, the need for persistent storage is foundational - something customers routinely cite as a top pain point. In his session at @DevOpsSummit at 21st Cloud Expo, Bill Borsari, Head of Systems Engineering at Datera, explored how organizations can reap the bene...
Using new techniques of information modeling, indexing, and processing, new cloud-based systems can support cloud-based workloads previously not possible for high-throughput insurance, banking, and case-based applications. In his session at 18th Cloud Expo, John Newton, CTO, Founder and Chairman of Alfresco, described how to scale cloud-based content management repositories to store, manage, and retrieve billions of documents and related information with fast and linear scalability. He addresse...
SYS-CON Events announced today that DatacenterDynamics has been named “Media Sponsor” of 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. DatacenterDynamics is a brand of DCD Group, a global B2B media and publishing company that develops products to help senior professionals in the world's most ICT dependent organizations make risk-based infrastructure and capacity decisions.
Discussions of cloud computing have evolved in recent years from a focus on specific types of cloud, to a world of hybrid cloud, and to a world dominated by the APIs that make today's multi-cloud environments and hybrid clouds possible. In this Power Panel at 17th Cloud Expo, moderated by Conference Chair Roger Strukhoff, panelists addressed the importance of customers being able to use the specific technologies they need, through environments and ecosystems that expose their APIs to make true ...
In his keynote at 19th Cloud Expo, Sheng Liang, co-founder and CEO of Rancher Labs, discussed 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 Docker c...