|By Jason Bloomberg||
|May 21, 2013 03:30 PM EDT||
When ZapThink last wrote about Business Process Management (BPM) in the Cloud in March 2012, we challenged both vendors and BPM customers to rethink their approach to BPM software, eschewing a heavyweight middleware approach for the lightweight, hypermedia-oriented approach that Representational State Transfer (REST) encourages. And while we did generate some short-lived buzz, most of the response – or lack thereof – was little more than a resounding silence.
True, work on Cloud-friendly, REST-based BPM continues in certain dusty corners of academia, most notably in the research of Cesare Pautasso, a professor at the University of Lugano in Switzerland. But in spite of his notable contributions to Thomas Erl’s SOA with REST book, the enterprise software and Cloud marketplaces have largely either ignored or misunderstood his research as well as ZapThink’s on this topic.
While it’s amusing to theorize a vast vendor conspiracy, positing middleware dinosaurs actively working to distract their customer base from lighter weight, Cloud-friendly approaches, the reality is likely to be far more mundane. People just don’t get it. Or to be precise, our audience doesn’t get how all the pieces—BPM, REST, Cloud, and even a bit of SOA—fit together. To help resolve this confusion, let’s resort to an age-old technique: let’s draw some pictures.
Framing the Cloud-Friendly BPM Problem
Let’s start this discussion with an illustration of an admittedly simplistic business process involving one person and some back-end system, as shown in Figure 1 below.
Note that in the figure above, the user might tackle a few tasks, and then the server takes over, executing a few tasks on its own. While the server is busy doing its thing, the user might query the server as to the current status of the process.
So far so good, but we don’t want our server to serve only one user at a time. After all, the whole point of the client/server pattern is that it is many to one. As a result, we need to introduce the notion of a process instance. For the sake of simplicity let’s assume that we don’t have more than one person participating in a particular instance at the same time. But we might have multiple people each running their own instance of a process, for example, completing a purchase on a Web site, as shown in Figure 2 below.
In the figure above, the BPM engine running on the server spawns a process instance to deal with the interactions with the user. If multiple users initiate the same process, the server can instantiate as many process instances as necessary, and the engine keeps track of where every user is in their instance—in other words, the instance state.
How to keep track of all this state information in a scalable, robust manner is at the core of numerous distributed computing challenges. Today’s BPM engines generally run on Enterprise Service Buses (ESBs), which maintain state by spawning threads—short-lived, specialized object instances that run in the execution environment of the ESB. But while threads are short-lived, process instances might take days or weeks to complete, and furthermore, threads are specific to the execution environment, making cross-ESB processes difficult to implement. For these reasons, we call state management the Achilles Heel of traditional, heavyweight (Web Services-based) SOA.
If such ESB-centric issues weren’t bad enough, the Cloud introduces a new wrinkle. Because we want to run our server in the Cloud, we don’t want to use it to maintain any state information, because we expect virtual machine (VM) instances to fail. In the Cloud, we provide automated recovery from failure rather than avoiding failure. However, if we store all the state information in the underlying persistence tier (not shown), then we limit our scalability, since every time anyone clicks a link, we must update a database somewhere.
What we need is a better way of dealing with state information that both allows our BPM engines to be Cloud friendly, and also frees us from the limitations of our ESBs. Or perhaps we must reinvent our ESBs to work in the Cloud. However you slice the problem, Hypermedia-Oriented Architecture (HOA) has the answer.
HOA to the Rescue
As ZapThink has discussed before, many people misconstrue REST as an API style that features a uniform interface, where in reality it’s a style of software architecture for building hypermedia systems. Why is the latter definition a better one? Because Roy Fielding, its creator, says so. That being said, work continues on the architectural context of REST, perhaps extending Fielding’s original thinking, as well as beyond the API style that most techies think of when they think about REST. We call this extension of the REST architectural style Hypermedia-Oriented Architecture, or HOA.
The central principle of HOA is the HATEOAS REST constraint: hypermedia is the engine of application state. In essence, HOA separates two different types of state information: application state and resource state. Application state corresponds to the user’s place in the runtime workflow consisting of hyperlinked representations, while resource state remains on the server, keeping track of persisted state information and state information that multiple users share.
On the one hand, HATEOAS requires hypermedia to manage all state information specific to individual clients, and on the other hand, delegates all other state information to the server. REST also specifies a set of verbs for querying an changing state information: GET for querying resource state without changing it, and three verbs that change the resource state: POST for initializing a resource, PUT for updating a resource, and DELETE for deleting a resource (assuming we’re using HTTP as our transport protocol).
Note, therefore, that all verbs other than GET change the resource state, while all verbs, including GET, change the application state. Furthermore, all state information appears in the messages between client and server: the requests from client to resource, and the representations from resource to client. By extension, HATEOAS requires us to only use POST, PUT, or DELETE when—and only when—we must update resource state.
With this principle in mind, we have a real problem with the process in Figure 2. Note that the server is maintaining application state, which HOA forbids. But we can’t solve this problem simply by picking up the process instance from the server and sticking it in the client and expecting it to work properly, because sometimes we really do want to update the resource state. We somehow need to separate the process instance into two (or more) pieces so that hypermedia on the client can be the engine of application state while the BPM engine remains the engine of resource state.
Figure 3 below illustrates this principle. The client sends a POST to the server, which initializes a resource. In this case, that new resource sends a hypermedia representation to a stateless intermediary which caches the representation. This hypermedia representation is essentially an abstraction of a dynamic set of hyperlinked representations, for example, one or more php scripts that can generate a set of hyperlinked Web pages. Once the intermediary has the hypermedia representation, it returns the initial representation (for instance, a Web page) to the client.
From that point on, as long as the client is navigating the application via hypermedia, changing only the application state as the user moves from one step in the process to the next, there is no need to change the resource state—and thus, no further POSTs, PUTs, or DELETEs are allowed. The client may perform a GET, because GETs change only the application state. The intermediary may be able to handle the GET on its own (if the necessary information is resident in the cache) or can turn around and perform a GET on an underlying resource, if necessary.
Furthermore, the application state may change without any interactions with the intermediary or the server by leveraging programmatic capabilities on the client. If the client is an arbitrary piece of software then this capability is trivial. But even if the client is a browser, it’s possible to change the state of an application without fetching anything from the server. In fact, there are many was to accomplish this feat.
Sometimes, of course, a hypermedia application, which we might also call a HOA process, must update resource state, for example, when it’s time to process the user’s credit card or change the number of widgets in inventory. Then—and only then—do we perform a PUT.
The most important characteristic of the process in Figure 3 is the fact that the intermediary is entirely stateless. If for some reason the VM that is hosting the hypermedia representation that is serving the client crashes, the Cloud environment must simply spawn a replacement and reload the same hypermedia representation as before. The client won’t lose its place because the hypermedia on the client are maintaining the application state. Similarly, we can horizontally scale the middle tier however and whenever we like. Instead of one VM hosting a particular hypermedia representation, we could have two or a hundred, and it doesn’t matter which one responds to a particular GET from the client.
Combining HOA Processes and Traditional BPM
The problem with the example in Figure 3, of course, is that every client’s process is separate from every other client’s process. However, most business processes in today’s organizations involve multiple parties—either multiple people or multiple enterprise applications or some combination.
On first glance, HOA doesn’t address such complex processes, since HATEOAS only deals with application state, not resource state. Fortunately, HOA works perfectly fine in this broader context as well, because it calls for a separation of application and resource state while providing for multiple ways to update resource state. After all, POST, PUT, and DELETE all update resource state, and any user can execute these verbs for a particular resource. Figure 4 below illustrates this more complex process.
In the figure above, a POST from a client instructs the BPM engine to instantiate a process instance on the server as in Figure 2. The first step in this process creates a hypermedia representation for the client to interact with as in Figure 3. Meanwhile, the resource state may change via any event, including a server-generated event or the action of a different user. If a user executes a PUT on the client to the hypermedia representation on the intermediary, then that representation turns around and PUTs to the appropriate underlying resource. Or perhaps the client PUTs to an underlying resource directly. Either way, the PUT goes to a hyperlink the client obtained from a previous representation at an earlier step in the process.
We might call the process running on the server a Composite RESTful Service, because the intermediary may abstract the entire server-based process via one or more RESTful URIs. A simple example of a Composite RESTful Service is a chat window application. Multiple users share the same chat session, so clearly the chat session state is part of the resource state.
There are a few essential points to keep in mind about the illustration in Figure 4. First, the intermediary remains stateless and therefore Cloud-friendly. We must maintain resource state in the persistence tier, but since we’ve offloaded the maintenance of application state to the client, we won’t be overburdening our database. We may also interact with our Composite RESTful Service via RESTful interactions, an essential benefit that Prof. Pautasso emphasizes in his research. And finally, not only is the middle tier horizontally scalable and elastic, so is the client tier—because every user brings their own client to the process.
The ZapThink Take
With the addition of an appropriate approach to building a RESTful Service abstraction, Figure 4 also serves as an illustration of how to implement RESTful SOA, what ZapThink refers to as “next generation” SOA in our Licensed ZapThink Architect (LZA) course as well as in my new book, The Agile Architecture Revolution. We therefore have a single, simple diagram bring together the worlds of SOA, BPM, Cloud, REST, and HOA.
The secret to getting all these architectural trends to work well together centers on how we deal with state information. We must first separate application state from resource state, and then subsequently take the conceptual leap to understanding that the best way to implement our business processes is by combining HOA processes with Composite RESTful Services. Once we make this leap, however, the pieces of this complicated puzzle finally fall into place.
Image credit: Bruce Guenter
How will your company move to the cloud while ensuring a solid security posture? Organizations from small to large are increasingly adopting cloud solutions to deliver essential business services at a much lower cost. According to cyber security experts, the frequency and severity of cyber-attacks are on the rise, causing alarm to businesses and customers across a variety of industries. To defend against exploits like these, a company must adopt a comprehensive security defense strategy that is ...
May. 28, 2016 12:00 PM EDT Reads: 514
SYS-CON Events announced today that ContentMX, the marketing technology and services company with a singular mission to increase engagement and drive more conversations for enterprise, channel and SMB technology marketers, has been named “Sponsor & Exhibitor Lounge Sponsor” of SYS-CON's 18th Cloud Expo, which will take place on June 7-9, 2016, at the Javits Center in New York City, New York. “CloudExpo is a great opportunity to start a conversation with new prospects, but what happens after the...
May. 28, 2016 11:15 AM EDT Reads: 1,196
SYS-CON Events announced today the How to Create Angular 2 Clients for the Cloud Workshop, being held June 7, 2016, in conjunction with 18th Cloud Expo | @ThingsExpo, at the Javits Center in New York, NY. Angular 2 is a complete re-write of the popular framework AngularJS. Programming in Angular 2 is greatly simplified. Now it’s a component-based well-performing framework. The immersive one-day workshop led by Yakov Fain, a Java Champion and a co-founder of the IT consultancy Farata Systems and...
May. 28, 2016 11:00 AM EDT Reads: 4,041
In his session at 18th Cloud Expo, Andrew Cole, Director of Solutions Engineering at Peak 10, will discuss how the newest technology advances are reducing the cost and complexity of traditional business continuity and disaster recovery solutions. Attendees will: Learn why having a full disaster recovery strategy is more important now than ever before Explore the key drivers of a successful disaster recovery solution Achieve measurable operational and business value from a disaster recovery ...
May. 28, 2016 11:00 AM EDT Reads: 1,406
Customer experience has become a competitive differentiator for companies, and it’s imperative that brands seamlessly connect the customer journey across all platforms. With the continued explosion of IoT, join us for a look at how to build a winning digital foundation in the connected era – today and in the future. In his session at @ThingsExpo, Chris Nguyen, Group Product Marketing Manager at Adobe, will discuss how to successfully leverage mobile, rapidly deploy content, capture real-time d...
May. 28, 2016 10:45 AM EDT Reads: 1,612
SYS-CON Events announced today that Hanu Software 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. Leveraging best-in-class people, processes, and technologies, Hanu provides high-quality, high-value software development and business process outsourcing services to independent software vendors (ISVs) and enterprises.
May. 28, 2016 10:30 AM EDT Reads: 1,377
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...
May. 28, 2016 10:00 AM EDT Reads: 515
SYS-CON Events announced today that BMC Software has been named "Siver Sponsor" of SYS-CON's 18th Cloud Expo, which will take place on June 7-9, 2015 at the Javits Center in New York, New York. BMC is a global leader in innovative software solutions that help businesses transform into digital enterprises for the ultimate competitive advantage. BMC Digital Enterprise Management is a set of innovative IT solutions designed to make digital business fast, seamless, and optimized from mainframe to mo...
May. 28, 2016 09:45 AM EDT Reads: 2,252
As organizations shift towards IT-as-a-service models, the need for managing and protecting data residing across physical, virtual, and now cloud environments grows with it. Commvault can ensure protection, access and E-Discovery of your data – whether in a private cloud, a Service Provider delivered public cloud, or a hybrid cloud environment – across the heterogeneous enterprise. In his general session at 18th Cloud Expo, Randy De Meno, Chief Technologist - Windows Products and Microsoft Part...
May. 28, 2016 09:45 AM EDT Reads: 592
What a difference a year makes. Organizations aren’t just talking about IoT possibilities, it is now baked into their core business strategy. With IoT, billions of devices generating data from different companies on different networks around the globe need to interact. From efficiency to better customer insights to completely new business models, IoT will turn traditional business models upside down. In the new customer-centric age, the key to success is delivering critical services and apps wit...
May. 28, 2016 09:15 AM EDT Reads: 1,178
Join us at Cloud Expo | @ThingsExpo 2016 – June 7-9 at the Javits Center in New York City and November 1-3 at the Santa Clara Convention Center in Santa Clara, CA – and deliver your unique message in a way that is striking and unforgettable by taking advantage of SYS-CON's unmatched high-impact, result-driven event / media packages.
May. 28, 2016 09:00 AM EDT Reads: 2,420
In his keynote at 18th Cloud Expo, Andrew Keys, Co-Founder of ConsenSys Enterprise, will provide 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 ...
May. 28, 2016 08:45 AM EDT Reads: 1,970
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.
May. 28, 2016 08:00 AM EDT Reads: 2,555
SYS-CON Events announced today that MobiDev 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. MobiDev is a software company that develops and delivers turn-key mobile apps, websites, web services, and complex software systems for startups and enterprises. Since 2009 it has grown from a small group of passionate engineers and business managers to a full-scale mobile software company with over 200 develope...
May. 28, 2016 07:15 AM EDT Reads: 2,654
SoftLayer operates a global cloud infrastructure platform built for Internet scale. With a global footprint of data centers and network points of presence, SoftLayer provides infrastructure as a service to leading-edge customers ranging from Web startups to global enterprises. SoftLayer's modular architecture, full-featured API, and sophisticated automation provide unparalleled performance and control. Its flexible unified platform seamlessly spans physical and virtual devices linked via a world...
May. 28, 2016 06:00 AM EDT Reads: 2,243