Microservices Expo Authors: Jason Bloomberg, Elizabeth White, Carmen Gonzalez, Pat Romanski, AppNeta Blog

Related Topics: @CloudExpo, Java IoT, Microservices Expo, Open Source Cloud, Agile Computing, Apache

@CloudExpo: Article

The Power of Opacity in REST

There’s more to the opacity story than opaque URIs

Ever wonder how a sophisticated Web site works? Take Facebook, for example. You can view the source and you can hardly pick out any recognizable HTML, let alone divine how the wizards back at Facebook HQ get the site to work. Now, try viewing the source at a simpler Web site, like ZapThink’s. Sure enough, there’s HTML under the covers, but you still can’t tell from the file the Web server sends to your browser what’s going on behind the scenes (we use WordPress, in case you were wondering).

Put into RESTful terms, there is a separation between resource (e.g., the program running on the server) and the representation (e.g., the Web page it sends to your browser). In fact, this separation is a fundamental REST constraint which allows the resource to be opaque.

When people talk about opacity in the REST context, they are usually referring to Uniform Resource Indicators (URIs). You should be able to construct URIs however you like, the theory goes, and it’s up to the resource to figure out how to respond appropriately. In other words, it’s not up to the client to know how to provide specific instructions to the server, other than by clicking the hyperlinks the resource has previously provided to the client.

But there’s more to the opacity story than opaque URIs. Fundamentally, the client has no way of knowing anything at all about what’s really going on behind the scenes. The resource might be a file, a script, a container, an object, or some complicated combination of these and other kinds of things. There are two important lessons for the techies behind the curtain: first, don’t assume resources come in one flavor, and second, it’s important to understand the full breadth of capabilities and patterns that you can leverage when architecting or building resources. After all, anything you can give a URI to can be a resource.

Exploring the Power of Opacity
Let’s begin our exploration of opacity with HTTP’s POST method. Of the four primary HTTP methods (GET, POST, PUT, and DELETE), POST is the only one that’s not idempotent: in other words, not only does it change the state of the resource, but it does so in a way that calling it twice has a different effect than calling it once. In the RESTful context, you should use POST to initialize a resource. According to the HTTP spec, POST creates a subordinate resource, as the figure below illustrates:

In the interaction above, the client POSTs to the cart resource, which initializes a cart instance, names it “abcde,” and returns a hyperlink to that new subordinate resource to the client. In this context, subordinate means that the abcde comes after cart and a slash in the URI http://example.com/cart/abcde.

Here’s the essential question: just what do cart and abcde represent on the server? cart looks like a directory and abcde looks like a file, given the pathlike structure of the URI. But we know that guess probably isn’t right, because POSTing to the cart resource actually created the abcde resource, which represents the cart instance. So could abcde be an object instance? Perhaps. The bottom line is you can’t tell, because as far as the client is concerned, it doesn’t matter. What matters is that the client now has one (or more) hyperlinks to its own cart that it can interact with via a uniform interface.

One way or the other, however, POST changes the state of the abcde cart instance, which requires a relatively onerous level of processing on the server. To lighten the future load on the server, thus improving its scalability, we may want to cache the representation the resource provides. Fortunately, REST explicitly supports cacheability, as the figure below illustrates:

In the pattern above, a gateway intermediary passes along the POST to the server, fetching a static representation it puts in its cache. As long as clients make requests that aren’t intended to change the state of the resource (namely, GETs), then serving up the cached copy is as good as passing along the request to the underlying resource, until the representation expires from the cache.

Opacity plays a critical role in this example as well, since saying the cached copy is just as good as a response directly from the resource is an example of opacity. As a result, the gateway is entirely transparent to the client, serving in the role of server in interactions with the client but in the role of client in interactions with the underlying server.

The limitation of the example above, of course, is the static nature of the cache. If the client wants to change the state of the resource (via PUT or another POST), then such a request would necessarily expire the cache, requiring the intermediary to pass the request along to the underlying server. In situations where the resource state changes frequently, therefore, caching is of limited value.

Opacity and RESTful Clouds
We can extend the pattern above to provide greater capabilities on the intermediary. In the example below, the intermediary is a full-fledged server in its own right, and the underlying server returns executable server scripts for the intermediary to execute on behalf of the underlying server. In other words, the intermediary caches representations that are themselves server programs (e.g., php scripts). Furthermore, these server scripts are prepopulated with any initial state data in response to the original POST from the client.

Increasing the sophistication of our cache would provide little value, however, if we didn’t have a better way of dealing with state information. Fortunately, REST grants our wishes in this case as well, because it enables us to separate resource state (maintained on the underlying server) from application state, which we can transfer to the client.

In the figure above, after the client has initialized the resource, it may wish to, say, update its cart. So, the user clicks a link that executes a PUT that sends the updated information, along with values from one or more hidden form fields to the intermediary. However, instead of updating resource state, the state information remains in the messages (both requests from the client and representations returned from the intermediary) as long as the client only executes idempotent requests. There is no need to update resource state in this situation, because the scripts on the intermediary know to pass along state information in hidden form fields, for example. When the cart process is complete and the user is ready to submit an order, only then does the client execute another POST, which the intermediary knows to pass along to the underlying server.

However, there’s no strict rule that says that the intermediary can only handle idempotent requests; you could easily put a script on it that would handle POSTs, and similarly, it might make sense to send an idempotent request like a DELETE along to the underlying server for execution. But on the other hand, the rule that the intermediary handles only the idempotent requests may be appropriate in your situation, because POST would then be the only method that could ever change state on the underlying server.

As we explained in an earlier ZapFlash, one of the primary benefits to following the pattern in the figure above is to support elasticity when you put the intermediary server in the Cloud. Because it is stateless, it doesn’t matter which virtual machine (VM) instance replies to any client request, and if a VM instance crashes, we can bootstrap its replacement without losing any state information. In other words, opacity is essential to both the elasticity and fault tolerance of the Cloud, and furthermore, following a RESTful approach provides that opacity.

The ZapThink Take
There’s one more RESTful pattern that ZapThink is particularly interested in: RESTful SOA, naturally. For this pattern we need another kind of intermediary: a RESTful SOA intermediary, in addition to the Cloud-based stateless server intermediary, or anything else we want to abstract for that matter. The figure below illustrates the RESTful SOA pattern.

The role of the RESTful SOA intermediary is to provide abstracted (in other words, opaque) RESTful Service endpoints that follow strict URI formatting rules. Furthermore, this intermediary must handle state information appropriately, that is, following a RESTful approach that transfers state information in messages. As a result, the SOA intermediary can support stateless message protocols for interactions with Service consumers while remaining stateless itself. Most ESBs maintain state, and therefore a RESTful SOA intermediary wouldn’t be a typical ESB, although it could certainly route messages to one.

So, which pattern is the best one? As we say in our Licensed ZapThink Architect (LZA) and Cloud Computing for Architects (CCA) courses, it depends. The architect is looking for the right tool for the job. You must understand the problem before recommending the appropriate solution. We cover REST-based SOA in our LZA course (coming to Johannesburg) and RESTful Clouds in the CCA course (coming to London, DC, and San Diego). See you there!

Image credit: Derek Keats

More Stories By Jason Bloomberg

Jason Bloomberg is the leading expert on architecting agility for the enterprise. As president of Intellyx, Mr. Bloomberg brings his years of thought leadership in the areas of Cloud Computing, Enterprise Architecture, and Service-Oriented Architecture to a global clientele of business executives, architects, software vendors, and Cloud service providers looking to achieve technology-enabled business agility across their organizations and for their customers. His latest book, The Agile Architecture Revolution (John Wiley & Sons, 2013), sets the stage for Mr. Bloomberg’s groundbreaking Agile Architecture vision.

Mr. Bloomberg is perhaps best known for his twelve years at ZapThink, where he created and delivered the Licensed ZapThink Architect (LZA) SOA course and associated credential, certifying over 1,700 professionals worldwide. He is one of the original Managing Partners of ZapThink LLC, the leading SOA advisory and analysis firm, which was acquired by Dovel Technologies in 2011. He now runs the successor to the LZA program, the Bloomberg Agile Architecture Course, around the world.

Mr. Bloomberg is a frequent conference speaker and prolific writer. He has published over 500 articles, spoken at over 300 conferences, Webinars, and other events, and has been quoted in the press over 1,400 times as the leading expert on agile approaches to architecture in the enterprise.

Mr. Bloomberg’s previous book, Service Orient or Be Doomed! How Service Orientation Will Change Your Business (John Wiley & Sons, 2006, coauthored with Ron Schmelzer), is recognized as the leading business book on Service Orientation. He also co-authored the books XML and Web Services Unleashed (SAMS Publishing, 2002), and Web Page Scripting Techniques (Hayden Books, 1996).

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).

@MicroservicesExpo Stories
By now, every company in the world is on the lookout for the digital disruption that will threaten their existence. In study after study, executives believe that technology has either already disrupted their industry, is in the process of disrupting it or will disrupt it in the near future. As a result, every organization is taking steps to prepare for or mitigate unforeseen disruptions. Yet in almost every industry, the disruption trend continues unabated.
SYS-CON Events announced today that HTBase will exhibit at SYS-CON's 20th International Cloud Expo®, which will take place on June 6-8, 2017, at the Javits Center in New York City, NY. HTBase (Gartner 2016 Cool Vendor) delivers a Composable IT infrastructure solution architected for agility and increased efficiency. It turns compute, storage, and fabric into fluid pools of resources that are easily composed and re-composed to meet each application’s needs. With HTBase, companies can quickly prov...
DevOps is often described as a combination of technology and culture. Without both, DevOps isn't complete. However, applying the culture to outdated technology is a recipe for disaster; as response times grow and connections between teams are delayed by technology, the culture will die. A Nutanix Enterprise Cloud has many benefits that provide the needed base for a true DevOps paradigm. In his Day 3 Keynote at 20th Cloud Expo, Chris Brown, a Solutions Marketing Manager at Nutanix, will explore t...
SYS-CON Events announced today that Auditwerx will exhibit at SYS-CON's 20th International Cloud Expo®, which will take place on June 6-8, 2017, at the Javits Center in New York City, NY. Auditwerx specializes in SOC 1, SOC 2, and SOC 3 attestation services throughout the U.S. and Canada. As a division of Carr, Riggs & Ingram (CRI), one of the top 20 largest CPA firms nationally, you can expect the resources, skills, and experience of a much larger firm combined with the accessibility and attent...
Everyone wants to use containers, but monitoring containers is hard. New ephemeral architecture introduces new challenges in how monitoring tools need to monitor and visualize containers, so your team can make sense of everything. In his session at @DevOpsSummit, David Gildeh, co-founder and CEO of Outlyer, will go through the challenges and show there is light at the end of the tunnel if you use the right tools and understand what you need to be monitoring to successfully use containers in your...
With major technology companies and startups seriously embracing Cloud strategies, now is the perfect time to attend @CloudExpo | @ThingsExpo, June 6-8, 2017, at the Javits Center in New York City, NY and October 31 - November 2, 2017, Santa Clara Convention Center, CA. Learn what is going on, contribute to the discussions, and ensure that your enterprise is on the right path to Digital Transformation.
What if you could build a web application that could support true web-scale traffic without having to ever provision or manage a single server? Sounds magical, and it is! In his session at 20th Cloud Expo, Chris Munns, Senior Developer Advocate for Serverless Applications at Amazon Web Services, will show how to build a serverless website that scales automatically using services like AWS Lambda, Amazon API Gateway, and Amazon S3. We will review several frameworks that can help you build serverle...
The IT industry is undergoing a significant evolution to keep up with cloud application demand. We see this happening as a mindset shift, from traditional IT teams to more well-rounded, cloud-focused job roles. The IT industry has become so cloud-minded that Gartner predicts that by 2020, this cloud shift will impact more than $1 trillion of global IT spending. This shift, however, has left some IT professionals feeling a little anxious about what lies ahead. The good news is that cloud computin...
Lots of cloud technology predictions and analysis are still dealing with future spending and planning, but there are plenty of real-world cloud use cases and implementations happening now. One approach, taken by stalwart GE, is to use SaaS applications for non-differentiated uses. For them, that means moving functions like HR, finance, taxes and scheduling to SaaS, while spending their software development time and resources on the core apps that make GE better, such as inventory, planning and s...
After more than five years of DevOps, definitions are evolving, boundaries are expanding, ‘unicorns’ are no longer rare, enterprises are on board, and pundits are moving on. Can we now look at an evolution of DevOps? Should we? Is the foundation of DevOps ‘done’, or is there still too much left to do? What is mature, and what is still missing? What does the next 5 years of DevOps look like? In this Power Panel at DevOps Summit, moderated by DevOps Summit Conference Chair Andi Mann, panelists l...
Without a clear strategy for cost control and an architecture designed with cloud services in mind, costs and operational performance can quickly get out of control. To avoid multiple architectural redesigns requires extensive thought and planning. Boundary (now part of BMC) launched a new public-facing multi-tenant high resolution monitoring service on Amazon AWS two years ago, facing challenges and learning best practices in the early days of the new service.
DevOps is often described as a combination of technology and culture. Without both, DevOps isn't complete. However, applying the culture to outdated technology is a recipe for disaster; as response times grow and connections between teams are delayed by technology, the culture will die. A Nutanix Enterprise Cloud has many benefits that provide the needed base for a true DevOps paradigm.
The rise of containers and microservices has skyrocketed the rate at which new applications are moved into production environments today. While developers have been deploying containers to speed up the development processes for some time, there still remain challenges with running microservices efficiently. Most existing IT monitoring tools don’t actually maintain visibility into the containers that make up microservices. As those container applications move into production, some IT operations t...
DevOps tends to focus on the relationship between Dev and Ops, putting an emphasis on the ops and application infrastructure. But that’s changing with microservices architectures. In her session at DevOps Summit, Lori MacVittie, Evangelist for F5 Networks, will focus on how microservices are changing the underlying architectures needed to scale, secure and deliver applications based on highly distributed (micro) services and why that means an expansion into “the network” for DevOps.
As Enterprise business moves from Monoliths to Microservices, adoption and successful implementations of Microservices become more evident. The goal of Microservices is to improve software delivery speed and increase system safety as scale increases. Documenting hurdles and problems for the use of Microservices will help consultants, architects and specialists to avoid repeating the same mistakes and learn how and when to use (or not use) Microservices at the enterprise level. The circumstance w...
Buzzword alert: Microservices and IoT at a DevOps conference? What could possibly go wrong? In this Power Panel at DevOps Summit, moderated by Jason Bloomberg, the leading expert on architecting agility for the enterprise and president of Intellyx, panelists peeled away the buzz and discuss the important architectural principles behind implementing IoT solutions for the enterprise. As remote IoT devices and sensors become increasingly intelligent, they become part of our distributed cloud enviro...
@DevOpsSummit has been named the ‘Top DevOps Influencer' by iTrend. iTrend processes millions of conversations, tweets, interactions, news articles, press releases, blog posts - and extract meaning form them and analyzes mobile and desktop software platforms used to communicate, various metadata (such as geo location), and automation tools. In overall placement, @DevOpsSummit ranked as the number one ‘DevOps Influencer' followed by @CloudExpo at third, and @MicroservicesE at 24th.
In his General Session at 16th Cloud Expo, David Shacochis, host of The Hybrid IT Files podcast and Vice President at CenturyLink, investigated three key trends of the “gigabit economy" though the story of a Fortune 500 communications company in transformation. Narrating how multi-modal hybrid IT, service automation, and agile delivery all intersect, he will cover the role of storytelling and empathy in achieving strategic alignment between the enterprise and its information technology.
While DevOps most critically and famously fosters collaboration, communication, and integration through cultural change, culture is more of an output than an input. In order to actively drive cultural evolution, organizations must make substantial organizational and process changes, and adopt new technologies, to encourage a DevOps culture. Moderated by Andi Mann, panelists discussed how to balance these three pillars of DevOps, where to focus attention (and resources), where organizations might...
Microservices are a very exciting architectural approach that many organizations are looking to as a way to accelerate innovation. Microservices promise to allow teams to move away from monolithic "ball of mud" systems, but the reality is that, in the vast majority of organizations, different projects and technologies will continue to be developed at different speeds. How to handle the dependencies between these disparate systems with different iteration cycles? Consider the "canoncial problem" ...