|By Jason Bloomberg||
|February 22, 2014 04:00 PM EST||
Whether you're a Cloud Computing aficionado, an enterprise integration specialist, or an IT executive, it's hard to have a conversation today without mention of REST. Representational State Transfer, or REST to the cognoscenti, is an architectural style that treats distributed computing problems as though they were Web problems. On the Web you have browsers chatting via HTTP to Web servers, and those servers can work whatever magic they need to in order to serve up the full wealth we've all come to expect from the World Wide Web. Take those basic Web patterns, extend them to general distributed computing problems (including Cloud and legacy integration), and voila! You have REST.
However, while REST has achieved substantial success in simplifying software interfaces and thus facilitating many forms of integration, it is still inherently inflexible. What works well for humans using browsers often doesn't apply to arbitrary software clients. And most fundamentally, REST does not address the most difficult distributed computing challenge of all: how to deal with dynamic business context.
Freeing Ourselves from REST's Four Constraints
The majority of RESTafarians, as the aforementioned cognoscenti have so eloquently dubbed themselves, treat REST as an Application Programming Interface (API) style. After all, REST does call for a uniform interface, a requirement that in one fell swoop addresses many of the knottier problems of Web Services and other, more tightly coupled API styles that came before. Compared to the complexities of Web Service operations or object-oriented remote method calls, REST's uniform interface is the essence of simplicity. Furthermore, there's no question that REST's uniform interface requirement is at the heart of what analysts like to refer to as the API Economy.
But there is more to REST than a uniform interface. In fact, REST isn't an API style at all. It's an architectural style. As an architectural style, REST consists of a set of constraints on software architecture. In other words, feel free to follow what architectural rules you like, but if you want to follow REST you must comply with the following RESTful constraints:
- Separation of resources from representations
- Manipulation of resources by representations
- Self-descriptive messages
- Hypermedia as the engine of application state, or HATEOAS
Let's take a quick tour of these constraints to put them in plain language. In so doing, we'll also why REST fails to adequately address the problem of dynamic business context.
The first constraint is essentially the encapsulation requirement. Resources are abstractions of capabilities on a server, while the representations are what the resources provide to the client. For example, a resource might be a php script running on a Web server, and the representation might be an HTML file it returns when a browser makes a GET request of it. But the browser never, ever gets the php itself; it only sees the HTML. The php is forever hidden from view.
The second constraint calls for the uniform interface. The only way that clients are able to interact with resources is by following hyperlinks in representations - in other words, making GET, POST, PUT, or DELETE requests to the URI of the resource, assuming we're using HTTP as our transport protocol, which we usually are.
The third, self-descriptive message constraint is actually quite straightforward: all the data as well as all the metadata the resource needs to process a request must be contained in that request, and correspondingly, the resource must send all necessary metadata in the representation response to the client that the client will need to understand the representation. In other words, REST requires that there be no out-of-band metadata: information pertinent to the interaction that doesn't actually appear in the interaction. Furthermore, the interaction must be stateless: the resource isn't expected to keep track of any information pertinent to any particular client.
The problem with this third constraint, of course, is that out-of-band metadata is very handy in many situations. Take security-related metadata, for example. REST calls for all such metadata to be in every request, which led to the development of the OAuth (Open Authorization) standard. Yes, OAuth is quite powerful and Web friendly. Yes, OAuth is making inroads into the enterprise. But do you really want to restrict the security protocols for all of your interactions to OAuth and nothing but OAuth? Probably not.
If you have a more complex interaction than a simple request, then the ban on out-of-band metadata becomes increasingly impractical. For example, let's say you're trying to support a complex business process by building a composite application. You're trying to follow REST so you're composing resources. But then you find you need to somehow deal with a range of policies, business rules, or other out-of-band metadata that impact the behavior of your composite application for certain users but not others. REST alone simply doesn't deal well with such complexities.
And then there's the fourth constraint: the dreaded HATEOAS. REST separates state information into two types: resource state and application state. Resource state is shared or persisted state information on the server, while application state is specific to the individual client, who negotiates the application (think abstracted Web site) by following hyperlinks. The HATEOAS constraint hammers home the fact that the point of REST is building distributed hypermedia systems, where the client is responsible for running hypermedia-based applications. In other words, the hypermedia contain the business context for the interactions between client and server.
Hypermedia drive the Web, of course, but once you start breaking down REST's notions of client and server, however, then the power of hypermedia starts to wane. After all, enterprises often want to build or leverage business applications that offer more than a simple Web site, especially when there's a shared business context across nodes, where those nodes are more than just clients and servers. Hypermedia - and REST - simply weren't built for such complex, dynamic situations.
The Devil in the Details
There's a very good reason why REST eschews out-of-band metadata and shared business context beyond the scope of hypermedia: both of these requirements are inherently dynamic, and furthermore, depend upon multiple actors - actors who may change over time. By constraining the architecture to avoid such complexities, REST provides a useful set of simplifications that have provided unquestionable value throughout the API economy.
The challenges in the section above, however, go well beyond REST. The problems we're discussing have plagued software interfaces in general, from the earliest screen-scraping programs to object-oriented APIs to Web Services to today's RESTful APIs. The entire notion of a software interface is an agreement between the people building the software provider and consumer endpoints that the interface behaves a particular way. Loose coupling, after all, relies upon an interface contract that fixes the behavior of the API so that the parties involved can make various decisions about their software under the covers without breaking the interaction. But woe to those who dare to change the contract, or who want to consider metadata the contract knows nothing about!
Out-of-band metadata and business context outside hypermedia applications are by definition exterior to the contract, and thus aren't amenable to any distributed computing architectural style that relies too heavily on static APIs. Therein lies the essential challenge of the API. To those analysts trumpeting the API Economy I say: the API Economy has nearly run its course. We've solved as many problems as we're going to solve with contracted software interfaces. But the business stakeholders still aren't happy. After all, it's their context - the business context - that APIs (whether RESTful or not) are so woefully unable to deal with. It's time for another approach.
The EnterpriseWeb Take
I'm not saying that we don't need APIs, of course, or that REST doesn't serve a useful purpose. I am declaring, however, that something critically important is missing from this picture. APIs are far too static to address issues of dynamic business context. We tried to address these issues with the SOA intermediary (typically an ESB), where the intermediary executed policy-based routing and transformation rules to abstract a set of inflexible Service interfaces, thus providing the illusion of flexibility, much as a flip deck provides the illusion of motion. But even the most successful implementers of SOA were still unable to deal with most out-of-band metadata - and dynamic business context? That nut no one has been able to crack.
What we really need is an entirely different kind of intermediary. A smarter intermediary that knows how to deal with all types of metadata and furthermore, can resolve the more difficult challenge of business context - in real time, where the business lives. In the next issue of Loosely-Coupled I'll discuss how such a smarter intermediary might actually work. And naturally, if you want to see one in action, drop us a line.
Image credit: lin440315
Peak 10, Inc., has announced the implementation of IT service management, a business process alignment initiative based on the widely adopted Information Technology Infrastructure Library (ITIL) framework. The implementation of IT service management enhances Peak 10’s current service-minded approach to IT delivery by propelling the company to deliver higher levels of personalized and prompt service. The majority of Peak 10’s operations employees have been trained and certified in the ITIL frame...
Apr. 29, 2016 07:30 AM EDT Reads: 803
As the rapid adoption of containers continues, companies are finding that they lack the operational tools to understand the behavior of applications deployed in these containers, and how to identify issues in their application infrastructure. For example, how are multiple containers within an application impacting each other’s performance? If an application’s service is degraded, which container is to blame? In the case of an application outage, what was the root cause of the outage?
Apr. 29, 2016 07:00 AM EDT Reads: 767
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.
Apr. 29, 2016 05:45 AM EDT Reads: 2,395
SYS-CON Events announced today TMCnet 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, and the 19th International Cloud Expo, which will take place on November 1–3, 2016, at the Santa Clara Convention Center in Santa Clara, CA. Technology Marketing Corporation (TMC) is the world's leading business-to-business and integrated marketing media company, servicing niche markets within the com...
Apr. 29, 2016 04:45 AM EDT Reads: 2,342
Between the mockups and specs produced by analysts, and resulting applications built by developers, there exists a gulf where projects fail, costs spiral, and applications disappoint. Methodologies like Agile attempt to address this with intensified communication, with partial success but many limitations. In his session at 18th Cloud Expo, Charles Kendrick, CTO & Chief Architect at Isomorphic Software, will present a revolutionary model enabled by new technologies. Learn how business and devel...
Apr. 29, 2016 03:45 AM EDT Reads: 1,641
Unless you don’t use the internet, don’t live in California, or haven’t been paying attention to the recent news… you should be aware that self-driving cars are on their way to becoming a reality. I have seen them – they are real. If you believe in the future reality of self-driving cars, then continue reading on. If you don’t believe in the future possibilities, then I am not sure what to do to convince you other than discuss the very real changes that will roll out with the consumer producti...
Apr. 28, 2016 09:45 PM EDT Reads: 368
If there is anything we have learned by now, is that every business paves their own unique path for releasing software- every pipeline, implementation and practices are a bit different, and DevOps comes in all shapes and sizes. Software delivery practices are often comprised of set of several complementing (or even competing) methodologies – such as leveraging Agile, DevOps and even a mix of ITIL, to create the combination that’s most suitable for your organization and that maximize your busines...
Apr. 28, 2016 08:45 PM EDT Reads: 1,724
In the rush to compete in the digital age, a successful digital transformation is essential, but many organizations are setting themselves up for failure. There’s a common misconception that the process is just about technology, but it’s not. It’s about your business. It shouldn’t be treated as an isolated IT project; it should be driven by business needs with the committed involvement of a range of stakeholders.
Apr. 28, 2016 07:30 PM EDT Reads: 1,768
New Relic, Inc. has announced a set of new features across the New Relic Software Analytics Cloud that offer IT operations teams increased visibility, and the ability to diagnose and resolve performance problems quickly. The new features further IT operations teams’ ability to leverage data and analytics, as well as drive collaboration and a common, shared understanding between teams. Software teams are under pressure to resolve performance issues quickly and improve availability, as the comple...
Apr. 28, 2016 07:15 PM EDT Reads: 2,373
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, will discuss 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 Technol...
Apr. 28, 2016 07:00 PM EDT Reads: 1,469
SYS-CON Events announced today that Enzu, a leading provider of cloud hosting solutions, 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. Enzu’s mission is to be the leading provider of enterprise cloud solutions worldwide. Enzu enables online businesses to use its IT infrastructure to their competitive advantage. By offering a suite of proven hosting and management services, Enzu wants companies to foc...
Apr. 28, 2016 05:30 PM EDT Reads: 827
Many private cloud projects were built to deliver self-service access to development and test resources. While those clouds delivered faster access to resources, they lacked visibility, control and security needed for production deployments. In their session at 18th Cloud Expo, Steve Anderson, Product Manager at BMC Software, and Rick Lefort, Principal Technical Marketing Consultant at BMC Software, will discuss how a cloud designed for production operations not only helps accelerate developer...
Apr. 28, 2016 05:00 PM EDT Reads: 992
Join IBM June 8 at 18th Cloud Expo at the Javits Center in New York City, NY, and learn how to innovate like a startup and scale for the enterprise. You need to deliver quality applications faster and cheaper, attract and retain customers with an engaging experience across devices, and seamlessly integrate your enterprise systems. And you can't take 12 months to do it.
Apr. 28, 2016 04:45 PM EDT Reads: 1,735
This is not a small hotel event. It is also not a big vendor party where politicians and entertainers are more important than real content. This is Cloud Expo, the world's longest-running conference and exhibition focused on Cloud Computing and all that it entails. If you want serious presentations and valuable insight about Cloud Computing for three straight days, then register now for Cloud Expo.
Apr. 28, 2016 04:30 PM EDT Reads: 1,622