Click here to close now.




Welcome!

@CloudExpo Authors: SmartBear Blog, Tom Kelly, Kevin Jackson, Elizabeth White, William Schmarzo

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).

@CloudExpo Stories
SYS-CON Events announced today that Men & Mice, the leading global provider of DNS, DHCP and IP address management overlay 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. The Men & Mice Suite overlay solution is already known for its powerful application in heterogeneous operating environments, enabling enterprises to scale without fuss. Building on a solid range of diverse platform support,...
Father business cycles and digital consumers are forcing enterprises to respond faster to customer needs and competitive demands. Successful integration of DevOps and Agile development will be key for business success in today’s digital economy. In his session at DevOps Summit, Pradeep Prabhu, Co-Founder & CEO of Cloudmunch, covered the critical practices that enterprises should consider to seamlessly integrate Agile and DevOps processes, barriers to implementing this in the enterprise, and pr...
Cognitive Computing is becoming the foundation for a new generation of solutions that have the potential to transform business. Unlike traditional approaches to building solutions, a cognitive computing approach allows the data to help determine the way applications are designed. This contrasts with conventional software development that begins with defining logic based on the current way a business operates. In her session at 18th Cloud Expo, Judith S. Hurwitz, President and CEO of Hurwitz & ...
SYS-CON Events announced today that Commvault, a global leader in enterprise data protection and information management, has been named “Bronze 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. Commvault is a leading provider of data protection and information management...
The cloud promises new levels of agility and cost-savings for Big Data, data warehousing and analytics. But it’s challenging to understand all the options – from IaaS and PaaS to newer services like HaaS (Hadoop as a Service) and BDaaS (Big Data as a Service). In her session at @BigDataExpo at @ThingsExpo, Hannah Smalltree, a director at Cazena, will provide an educational overview of emerging “as-a-service” options for Big Data in the cloud. This is critical background for IT and data profes...
SYS-CON Events announced today that VAI, a leading ERP software provider, 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. VAI (Vormittag Associates, Inc.) is a leading independent mid-market ERP software developer renowned for its flexible solutions and ability to automate critical business functions for the distribution, manufacturing, specialty retail and service sectors. An IBM Premier Business Part...
SYS-CON Events announced today that Alert Logic, Inc., the leading provider of Security-as-a-Service solutions for the cloud, 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. Alert Logic, Inc., provides Security-as-a-Service for on-premises, cloud, and hybrid infrastructures, delivering deep security insight and continuous protection for customers at a lower cost than traditional security solutions. Ful...
In most cases, it is convenient to have some human interaction with a web (micro-)service, no matter how small it is. A traditional approach would be to create an HTTP interface, where user requests will be dispatched and HTML/CSS pages must be served. This approach is indeed very traditional for a web site, but not really convenient for a web service, which is not intended to be good looking, 24x7 up and running and UX-optimized. Instead, talking to a web service in a chat-bot mode would be muc...
It's easy to assume that your app will run on a fast and reliable network. The reality for your app's users, though, is often a slow, unreliable network with spotty coverage. What happens when the network doesn't work, or when the device is in airplane mode? You get unhappy, frustrated users. An offline-first app is an app that works, without error, when there is no network connection.
SYS-CON Events announced today that Catchpoint Systems, Inc., a provider of innovative web and infrastructure monitoring solutions, has been named “Silver Sponsor” of SYS-CON's DevOps Summit at 18th Cloud Expo New York, which will take place June 7-9, 2016, at the Javits Center in New York City, NY. Catchpoint is a leading Digital Performance Analytics company that provides unparalleled insight into customer-critical services to help consistently deliver an amazing customer experience. Designed...
As someone who has been dedicated to automation and Application Release Automation (ARA) technology for almost six years now, one of the most common questions I get asked regards Platform-as-a-Service (PaaS). Specifically, people want to know whether release automation is still needed when a PaaS is in place, and why. Isn't that what a PaaS provides? A solution to the deployment and runtime challenges of an application? Why would anyone using a PaaS then need an automation engine with workflow ...
SYS-CON Events announced today that Interoute, owner-operator of one of Europe's largest networks and a global cloud services platform, has been named “Bronze 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. Interoute is the owner-operator of one of Europe's largest networks and a global cloud services platform which encompasses 12 data centers, 14 virtual data centers and 31 colocation centers, with connections to 195 ad...
More and more companies are looking to microservices as an architectural pattern for breaking apart applications into more manageable pieces so that agile teams can deliver new features quicker and more effectively. What this pattern has done more than anything to date is spark organizational transformations, setting the foundation for future application development. In practice, however, there are a number of considerations to make that go beyond simply “build, ship, and run,” which changes ho...
With an estimated 50 billion devices connected to the Internet by 2020, several industries will begin to expand their capabilities for retaining end point data at the edge to better utilize the range of data types and sheer volume of M2M data generated by the Internet of Things. In his session at @ThingsExpo, Don DeLoach, CEO and President of Infobright, will discuss the infrastructures businesses will need to implement to handle this explosion of data by providing specific use cases for filte...
SYS-CON Events announced today that AppNeta, the leader in performance insight for business-critical web applications, will exhibit and present at SYS-CON's @DevOpsSummit at Cloud Expo New York, which will take place on June 7-9, 2016, at the Javits Center in New York City, NY. AppNeta is the only application performance monitoring (APM) company to provide solutions for all applications – applications you develop internally, business-critical SaaS applications you use and the networks that deli...
SYS-CON Events announced today that Pythian, a global IT services company specializing in helping companies adopt disruptive technologies to optimize revenue-generating systems, has been named “Bronze 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. Founded in 1997, Pythian is a global IT services company that helps companies compete by adopting disruptive technologies such as cloud, Big Data, advanced analytics, and DevO...
Advances in technology and ubiquitous connectivity have made the utilization of a dispersed workforce more common. Whether that remote team is located across the street or country, management styles/ approaches will have to be adjusted to accommodate this new dynamic. In his session at 17th Cloud Expo, Sagi Brody, Chief Technology Officer at Webair Internet Development Inc., focused on the challenges of managing remote teams, providing real-world examples that demonstrate what works and what do...
As enterprises work to take advantage of Big Data technologies, they frequently become distracted by product-level decisions. In most new Big Data builds this approach is completely counter-productive: it presupposes tools that may not be a fit for development teams, forces IT to take on the burden of evaluating and maintaining unfamiliar technology, and represents a major up-front expense. In his session at @BigDataExpo at @ThingsExpo, Andrew Warfield, CTO and Co-Founder of Coho Data, will dis...
SYS-CON Events announced today that Fusion, a leading provider of cloud services, 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. Fusion, a leading provider of integrated cloud solutions to small, medium and large businesses, is the industry's single source for the cloud. Fusion's advanced, proprietary cloud service platform enables the integration of leading edge solutions in the cloud, including clou...
Your business relies on your applications and your employees to stay in business. Whether you develop apps or manage business critical apps that help fuel your business, what happens when users experience sluggish performance? You and all technical teams across the organization – application, network, operations, among others, as well as, those outside the organization, like ISPs and third-party providers – are called in to solve the problem.