Welcome!

Microservices Expo Authors: Yeshim Deniz, Pat Romanski, Todd Matters, Mark Leake, Stefana Muller

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

Microservices Expo: Article

Toss Your Cookies: Maintaining State on the Client with REST

Feel free to transfer application state to the client and rest assured you’re following REST.

REST quiz of the day: which is more important when following REST: updating the resource state or updating state on the client? Most developers are likely to say that REST focuses on updating resource state on the server. After all, POST, PUT, and DELETE all do so. GET is the only HTTP verb that fetches resource state without changing it.

If you've been reading ZapThink's discussion on REST, you probably realize that those developers are incorrect. Updating resource state is clearly an important part of REST, but updating state on the client is even more important. Why? Because client state is the foundation for distributed hypermedia applications. And after all, such applications are the point of REST.

In fact, the RESTful world distinguishes between resource state and application state, which is the state information the client maintains. And since hypermedia are the engine of application state, it makes sense that application state is more important to REST than resource state. After all, REST is representational state transfer. The representations are what the resources send to the clients, including application state information that belongs on the client.

HATEOAS and the Cloud
The topic of application state came up in an interesting discussion during our recent Cloud Computing for Architects course in San Diego. I was explaining how it's important to maintain a stateless application tier in the Cloud, because we want to put the components on that tier (Web servers, application servers, ESBs, etc.) onto virtual machine (VM) instances. In order to achieve the elasticity and resilience of the Cloud, then, we can't afford to maintain state information on such instances. We always have the option of persisting such state information, making it a part of the resource state, but relying too heavily on our resource state limits our scalability. The clear alternative is to transfer state information to the client, and let hypermedia be the engine of application state (otherwise known as the dreaded HATEOAS REST constraint).

One of the attendees in the class was confused by this discussion. He pointed out that if we use the client (say, a browser) to maintain state in a stateful application like an eCommerce shopping cart, then such state information must either go into hidden form fields or into the URL, so that the server can pass it along to the browser from one request to the next. But if the user is clicking a link rather than submitting a form, then they are executing a GET, and with a GET, the only place to put state information from the client to the server is in the URL. And we all know that URLs have a maximum length. What do we do, he asked, if we have too much state information for the URL? For example, we might have dozens of items in our cart. Was I suggesting passing the entire contents of each cart - product descriptions, prices, etc. - in the URL?

The answer, of course, is no. I say "of course" because such a question would be silly for anyone who truly understands REST. But I must admit, it took me a while to think through my response. The problem was that I have a background as a Web developer, and my student may have also built his share of Web sites back in the day as well. And back in the 1990s, before REST, in the early days of HTML and JavaScript, maintaining state in a browser was problematic. All we had were cookies and the aforementioned hidden form fields and URL query strings. And since people can turn their cookies off, we never wanted to rely on them. So yes, back in the day, if the user is clicking a link (i.e., performing a GET), the URL was all you had to work with.

With REST, however, we're working with an abstracted client. It need not be a browser, and in fact, it need not have a user interface at all. A RESTful client may serve as an intermediary, for example. Even when the client has a UI, it could be any type of application. For example, most mobile apps are written natively to the mobile environment (iPhone or Android, for the most part), and will continue to be at least until HTML5 is fully baked.

Even when the client is a browser, however, we have numerous ways of maintaining application state. Each approach, as you might expect, has its strengths and weaknesses:

  • Cookies - long a part of the HTTP protocol, cookies are universally supported and almost as universally reviled. We love them for enabling the "remember me" feature on Web sites with logins we visit frequently, and we hate them for enabling advertisers to track our browsing habits. Few app developers would rely on them for much else.
  • Hidden form fields - every Web developer's secret sauce. You can put whatever you want into such fields, and as long as the user submits the corresponding form, the contents of hidden fields go along for the ride. The problem is that hidden form fields only work with POST. In REST, POST is only for initializing a subsidiary resource, so if that's not what you're doing, then you don't want to POST. The other downside to hidden form fields is that application state information must always make a round trip to the server and back again, whether the server needs to do anything with it or not.
  • Frames - Frames made their debut in 1996 in Netscape Navigator 2.0, the same browser that introduced JavaScript to the world. Iframes came soon after. Both types of frames allowed new pages in the frame while maintaining state information in JavaScript variables in the enclosing page. In either case, however, updating the content of a frame doesn't change the URL in the browser's location field. As a result, reloading or following a bookmarked page takes you back to square one, deleting all state information.
  • JavaScript-only updates - More recent advances to the Document Object Model (DOM), in particular the innerHTML property, allow JavaScript to update any <div> element after the page is loaded. And since JavaScript can also perform all manner of RESTful calls, it's possible to make it appear that any or all of a page is changing, even though the page itself isn't actually reloading. As with frames, JavaScript variables can store state information, but also similar to frames, the URL the user sees doesn't change when your script interacts with the server.
  • Signed scripts - What about simply writing arbitrary content to the user's hard drive? Browser publishers have been monkeying with this capability since signed scripts debuted in the 1990s. The problem with giving the browser write privileges, of course, is security. One flaw and hackers can easily take over your computer. Needless to say, this capability never took off, although plugins like Adobe Flash can allow the ability to write to the users' hard drive.
  • DOM storage - Today we have DOM storage. Think cookies on steroids. Every modern browser can essentially store a JSON object that persists as the browser loads different pages. You have the option of maintaining such information for a browser session (you lose it when you quit the browser) or persisting it across browser sessions (where the browser writes the data to a file). This capability also enables developers to write browser apps that can function properly when the user is offline. The downside to DOM storage is that it only works in newer browsers - although Firefox, Internet Explorer, Chrome, and Safari all support it.
  • URL query string - finally, let's discuss storing state information in the URL. Yes, there's a character limit - the HTTP spec recommends sticking to 255 characters or less, although most browsers and Web servers support much longer URLs. So, how much can you cram into 255 characters? More than you might expect, if you use a tool like RISON for compacting JSON to squeeze more of it into each URL. Don't like RISON? There are alternatives available or you can create your own approach. Even with such techniques, however, there is still a size limit, and all such information must make the round trip to server and back.

The ZapThink Take
Based on the discussion above, you should have no more concerns about storing application state on the client. There are always tradeoffs, but one of the scenarios above should handle virtually every application state issue you're likely to come up with. Feel free to transfer application state to the client and rest assured you're following REST.

That is, of course, if you really are following REST, which means that you're building a hypermedia application. And while POST, PUT, and DELETE update resource state for hypermedia applications, every representation from resource back to client updates client state. Even a GET, which never changes resource state, still changes the application state. In other words, clicking a link or submitting a form loads a new page. Of course REST behaves that way.

While this article focused more on maintaining state on the client, therefore, REST is more concerned with updating state on the client. The real point here is that we have the luxury of choosing to maintain the state information we require while running an application whose state is supposed to change. Either way, hypermedia are the engine of application state.

Image source: bloggyboulga

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
Cloud Expo, Inc. has announced today that Andi Mann and Aruna Ravichandran have been named Co-Chairs of @DevOpsSummit at Cloud Expo Silicon Valley which will take place Oct. 31-Nov. 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. "DevOps is at the intersection of technology and business-optimizing tools, organizations and processes to bring measurable improvements in productivity and profitability," said Aruna Ravichandran, vice president, DevOps product and solutions marketing...
"When we talk about cloud without compromise what we're talking about is that when people think about 'I need the flexibility of the cloud' - it's the ability to create applications and run them in a cloud environment that's far more flexible,” explained Matthew Finnie, CTO of Interoute, in this SYS-CON.tv interview at 20th Cloud Expo, held June 6-8, 2017, at the Javits Center in New York City, NY.
For most organizations, the move to hybrid cloud is now a question of when, not if. Fully 82% of enterprises plan to have a hybrid cloud strategy this year, according to Infoholic Research. The worldwide hybrid cloud computing market is expected to grow about 34% annually over the next five years, reaching $241.13 billion by 2022. Companies are embracing hybrid cloud because of the many advantages it offers compared to relying on a single provider for all of their cloud needs. Hybrid offers bala...
A common misconception about the cloud is that one size fits all. Companies expecting to run all of their operations using one cloud solution or service must realize that doing so is akin to forcing the totality of their business functionality into a straightjacket. Unlocking the full potential of the cloud means embracing the multi-cloud future where businesses use their own cloud, and/or clouds from different vendors, to support separate functions or product groups. There is no single cloud so...
Containers, microservices and DevOps are all the rage lately. You can read about how great they are and how they’ll change your life and the industry everywhere. So naturally when we started a new company and were deciding how to architect our app, we went with microservices, containers and DevOps. About now you’re expecting a story of how everything went so smoothly, we’re now pushing out code ten times a day, but the reality is quite different.
"We are a monitoring company. We work with Salesforce, BBC, and quite a few other big logos. We basically provide monitoring for them, structure for their cloud services and we fit into the DevOps world" explained David Gildeh, Co-founder and CEO of Outlyer, in this SYS-CON.tv interview at DevOps Summit at 20th Cloud Expo, held June 6-8, 2017, at the Javits Center in New York City, NY.
21st International Cloud Expo, taking place October 31 - November 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA, will feature technical sessions from a rock star conference faculty and the leading industry players in the world. Cloud computing is now being embraced by a majority of enterprises of all sizes. Yesterday's debate about public vs. private has transformed into the reality of hybrid cloud: a recent survey shows that 74% of enterprises have a hybrid cloud strategy. Me...
If you cannot explicitly articulate how investing in a new technology, changing the approach or re-engineering the business process will help you achieve your customer-centric vision of the future in direct and measurable ways, you probably shouldn’t be doing it. At Intellyx, we spend a lot of time talking to technology vendors. In our conversations, we explore emerging new technologies that are either disrupting the way enterprise organizations work or that help enable those organizations to ...
In 2014, Amazon announced a new form of compute called Lambda. We didn't know it at the time, but this represented a fundamental shift in what we expect from cloud computing. Now, all of the major cloud computing vendors want to take part in this disruptive technology. In his session at 20th Cloud Expo, Doug Vanderweide, an instructor at Linux Academy, discussed why major players like AWS, Microsoft Azure, IBM Bluemix, and Google Cloud Platform are all trying to sidestep VMs and containers wit...
The taxi industry never saw Uber coming. Startups are a threat to incumbents like never before, and a major enabler for startups is that they are instantly “cloud ready.” If innovation moves at the pace of IT, then your company is in trouble. Why? Because your data center will not keep up with frenetic pace AWS, Microsoft and Google are rolling out new capabilities. In his session at 20th Cloud Expo, Don Browning, VP of Cloud Architecture at Turner, posited that disruption is inevitable for comp...
For organizations that have amassed large sums of software complexity, taking a microservices approach is the first step toward DevOps and continuous improvement / development. Integrating system-level analysis with microservices makes it easier to change and add functionality to applications at any time without the increase of risk. Before you start big transformation projects or a cloud migration, make sure these changes won’t take down your entire organization.
There's a lot to gain from cloud computing, but success requires a thoughtful and enterprise focused approach. Cloud computing decouples data and information from the infrastructure on which it lies. A process that is a LOT more involved than dragging some folders from your desktop to a shared drive. Cloud computing as a mission transformation activity, not a technological one. As an organization moves from local information hosting to the cloud, one of the most important challenges is addressi...
What's the role of an IT self-service portal when you get to continuous delivery and Infrastructure as Code? This general session showed how to create the continuous delivery culture and eight accelerators for leading the change. Don Demcsak is a DevOps and Cloud Native Modernization Principal for Dell EMC based out of New Jersey. He is a former, long time, Microsoft Most Valuable Professional, specializing in building and architecting Application Delivery Pipelines for hybrid legacy, and cloud ...
Companies have always been concerned that traditional enterprise software is slow and complex to install, often disrupting critical and time-sensitive operations during roll-out. With the growing need to integrate new digital technologies into the enterprise to transform business processes, this concern has become even more pressing. A 2016 Panorama Consulting Solutions study revealed that enterprise resource planning (ERP) projects took an average of 21 months to install, with 57 percent of t...
Microservices are increasingly used in the development world as developers work to create larger, more complex applications that are better developed and managed as a combination of smaller services that work cohesively together for larger, application-wide functionality. Tools such as Service Fabric are rising to meet the need to think about and build apps using a piece-by-piece methodology that is, frankly, less mind-boggling than considering the whole of the application at once. Today, we'll ...
In his session at Cloud Expo, Alan Winters, an entertainment executive/TV producer turned serial entrepreneur, presented a success story of an entrepreneur who has both suffered through and benefited from offshore development across multiple businesses: The smart choice, or how to select the right offshore development partner Warning signs, or how to minimize chances of making the wrong choice Collaboration, or how to establish the most effective work processes Budget control, or how to ma...
Hybrid IT is today’s reality, and while its implementation may seem daunting at times, more and more organizations are migrating to the cloud. In fact, according to SolarWinds 2017 IT Trends Index: Portrait of a Hybrid IT Organization 95 percent of organizations have migrated crucial applications to the cloud in the past year. As such, it’s in every IT professional’s best interest to know what to expect.
Both SaaS vendors and SaaS buyers are going “all-in” to hyperscale IaaS platforms such as AWS, which is disrupting the SaaS value proposition. Why should the enterprise SaaS consumer pay for the SaaS service if their data is resident in adjacent AWS S3 buckets? If both SaaS sellers and buyers are using the same cloud tools, automation and pay-per-transaction model offered by IaaS platforms, then why not host the “shrink-wrapped” software in the customers’ cloud? Further, serverless computing, cl...
In the decade following his article, cloud computing further cemented Carr’s perspective. Compute, storage, and network resources have become simple utilities, available at the proverbial turn of the faucet. The value they provide is immense, but the cloud playing field is amazingly level. Carr’s quote above presaged the cloud to a T. Today, however, we’re in the digital era. Mark Andreesen’s ‘software is eating the world’ prognostication is coming to pass, as enterprises realize they must be...
Colocation is a central pillar of modern enterprise infrastructure planning because it provides greater control, insight, and performance than managed platforms. In spite of the inexorable rise of the cloud, most businesses with extensive IT hardware requirements choose to host their infrastructure in colocation data centers. According to a recent IDC survey, more than half of the businesses questioned use colocation services, and the number is even higher among established businesses and busin...