|By Jason Bloomberg||
|December 17, 2012 08:45 AM EST||
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?
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.
- 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
The 5th International DevOps Summit, co-located with 17th International Cloud Expo – being held November 3-5, 2015, at the Santa Clara Convention Center in Santa Clara, CA – announces that its Call for Papers is open. Born out of proven success in agile development, cloud computing, and process automation, DevOps is a macro trend you cannot afford to miss. From showcase success stories from early adopters and web-scale businesses, DevOps is expanding to organizations of all sizes, including the...
Apr. 28, 2015 03:00 PM EDT Reads: 2,302
Health care systems across the globe are under enormous strain, as facilities reach capacity and costs continue to rise. M2M and the Internet of Things have the potential to transform the industry through connected health solutions that can make care more efficient while reducing costs. In fact, Vodafone's annual M2M Barometer Report forecasts M2M applications rising to 57 percent in health care and life sciences by 2016. Lively is one of Vodafone's health care partners, whose solutions enable o...
Apr. 28, 2015 03:00 PM EDT Reads: 1,603
Modern Systems announced completion of a successful project with its new Rapid Program Modernization (eavRPMa"c) software. The eavRPMa"c technology architecturally transforms legacy applications, enabling faster feature development and reducing time-to-market for critical software updates. Working with Modern Systems, the University of California at Santa Barbara (UCSB) leveraged eavRPMa"c to transform its Student Information System from Software AG's Natural syntax to a modern application lev...
Apr. 28, 2015 02:15 PM EDT Reads: 1,879
Public Cloud IaaS started it's life in the developer and startup communities and has grown rapidly to a $20B+ industry, but it still pales in comparison to how much is spent worldwide on IT: $3.6 trillion. In fact, there are 8.6 million data centers worldwide, the reality is many small and medium sized business have server closets and colocation footprints filled with servers and storage gear. While on-premise environment virtualization may have peaked at 75%, the Public Cloud has lagged in ado...
Apr. 28, 2015 02:00 PM EDT Reads: 1,423
Dave will share his insights on how Internet of Things for Enterprises are transforming and making more productive and efficient operations and maintenance (O&M) procedures in the cleantech industry and beyond. Speaker Bio: Dave Landa is chief operating officer of Cybozu Corp (kintone US). Based in the San Francisco Bay Area, Dave has been on the forefront of the Cloud revolution driving strategic business development on the executive teams of multiple leading Software as a Services (SaaS) ap...
Apr. 28, 2015 02:00 PM EDT Reads: 1,718
SYS-CON Events announced today that Secure Infrastructure & Services will exhibit at SYS-CON's 16th International Cloud Expo®, which will take place on June 9-11, 2015, at the Javits Center in New York City, NY, and the 17th International Cloud Expo®, which will take place on November 3–5, 2015, at the Santa Clara Convention Center in Santa Clara, CA. Secure Infrastructure & Services (SIAS) is a managed services provider of cloud computing solutions for the IBM Power Systems market. The company...
Apr. 28, 2015 01:30 PM EDT Reads: 452
SYS-CON Events announced today that CenturyLink, Inc., a leader in the network services market, has been named “Platinum Sponsor” of SYS-CON's 16th International Cloud Expo®, which will take place on June 9-11, 2015, at the Javits Center in New York City, NY. CenturyLink is the third largest telecommunications company in the United States and is recognized as a leader in the network services market by technology industry analyst firms. The company is a global leader in cloud infrastructure and ...
Apr. 28, 2015 01:02 PM EDT Reads: 506
Docker, Inc., has been included in the list of "Cool Vendors" in the April 21, 2015 report by Gartner, Inc, Cool Vendors in DevOps, 2015. In the report, Gartner notes, “As virtualization and cloud applications grow beyond being single images run on premise to being comprised of multiple tiers that can be run and scaled in a hybrid cloud, new approaches are needed to reduce complexity.” “Docker has gained great traction within the developer community for how efficient it makes the individual de...
Apr. 28, 2015 01:00 PM EDT Reads: 427
From telemedicine to smart cars, digital homes and industrial monitoring, the explosive growth of IoT has created exciting new business opportunities for real time calls and messaging. In his session at @ThingsExpo, Ivelin Ivanov, CEO and Co-Founder of Telestax, shared some of the new revenue sources that IoT created for Restcomm – the open source telephony platform from Telestax. Ivelin Ivanov is a technology entrepreneur who founded Mobicents, an Open Source VoIP Platform, to help create, de...
Apr. 28, 2015 12:00 PM EDT Reads: 5,328
SYS-CON Events announced today that B2Cloud, a provider of enterprise resource planning software, will exhibit at SYS-CON's 16th International Cloud Expo®, which will take place on June 9-11, 2015, at the Javits Center in New York City, NY. B2cloud develops the software you need. They have the ideal tools to help you work with your clients. B2Cloud’s main solutions include AGIS – ERP, CLOHC, AGIS – Invoice, and IZUM
Apr. 28, 2015 12:00 PM EDT Reads: 3,717
ProfitBricks has launched its new DevOps Central and REST API, along with support for three multi-cloud libraries and a Python SDK. This, combined with its already existing SOAP API and its new RESTful API, moves ProfitBricks into a position to better serve the DevOps community and provide the ability to automate cloud infrastructure in a multi-cloud world. Following this momentum, ProfitBricks has also introduced several libraries that enable developers to use their favorite language to code ...
Apr. 28, 2015 12:00 PM EDT Reads: 1,872
The IoT Bootcamp is coming to Cloud Expo | @ThingsExpo on June 9-10 at the Javits Center in New York. Instructor. Registration is now available at http://iotbootcamp.sys-con.com/ Instructor Janakiram MSV previously taught the famously successful Multi-Cloud Bootcamp at Cloud Expo | @ThingsExpo in November in Santa Clara. Now he is expanding the focus to Janakiram is the founder and CTO of Get Cloud Ready Consulting, a niche Cloud Migration and Cloud Operations firm that recently got acquir...
Apr. 28, 2015 12:00 PM EDT Reads: 1,790
The 17th International Cloud Expo has announced that its Call for Papers is open. 17th International Cloud Expo, to be held November 3-5, 2015, at the Santa Clara Convention Center in Santa Clara, CA, brings together Cloud Computing, APM, APIs, Microservices, Security, Big Data, Internet of Things, DevOps and WebRTC to one location. With cloud computing driving a higher percentage of enterprise IT budgets every year, it becomes increasingly important to plant your flag in this fast-expanding bu...
Apr. 28, 2015 12:00 PM EDT Reads: 2,493
Many of the well-known examples of DevOps success we read in blogs on the Internet paint an idyllic picture of DevOps productivity. A team was facing a stodgy, slow-moving operations department, teams weren’t delivering software on time. Those teams moved to DevOps, became proactive about infrastructure and deployment automation, and an overnight transition to productivity ensues. People are promoted, projects are successful, and developers and system administrators dance hand-in-hand in a final...
Apr. 28, 2015 11:15 AM EDT Reads: 1,389
SYS-CON Media announced today that @ThingsExpo Blog launched with 7,788 original stories. @ThingsExpo Blog offers top articles, news stories, and blog posts from the world's well-known experts and guarantees better exposure for its authors than any other publication. @ThingsExpo Blog can be bookmarked. The Internet of Things (IoT) is the most profound change in personal and enterprise IT since the creation of the Worldwide Web more than 20 years ago.
Apr. 28, 2015 11:00 AM EDT Reads: 2,712
As Marc Andreessen says software is eating the world. Everything is rapidly moving toward being software-defined – from our phones and cars through our washing machines to the datacenter. However, there are larger challenges when implementing software defined on a larger scale - when building software defined infrastructure. In his session at 16th Cloud Expo, Boyan Ivanov, CEO of StorPool, will provide some practical insights on what, how and why when implementing "software-defined" in the dat...
Apr. 28, 2015 11:00 AM EDT Reads: 1,812
SYS-CON Events announced today that robomq.io will exhibit at SYS-CON's @ThingsExpo, which will take place on June 9-11, 2015, at the Javits Center in New York City, NY. robomq.io is an interoperable and composable platform that connects any device to any application. It helps systems integrators and the solution providers build new and innovative products and service for industries requiring monitoring or intelligence from devices and sensors.
Apr. 28, 2015 11:00 AM EDT Reads: 2,194
SYS-CON Events announced today that MangoApps will exhibit at SYS-CON's 16th International Cloud Expo®, which will take place on June 9-11, 2015, at the Javits Center in New York City, NY., and the 17th International Cloud Expo®, which will take place on November 3–5, 2015, at the Santa Clara Convention Center in Santa Clara, CA. MangoApps provides private all-in-one social intranets allowing workers to securely collaborate from anywhere in the world and from any device. Social, mobile, and eas...
Apr. 28, 2015 11:00 AM EDT Reads: 3,787
Containers and microservices have become topics of intense interest throughout the cloud developer and enterprise IT communities. Accordingly, attendees at the upcoming 16th Cloud Expo at the Javits Center in New York June 9-11 will find fresh new content in a new track called PaaS | Containers & Microservices Containers are not being considered for the first time by the cloud community, but a current era of re-consideration has pushed them to the top of the cloud agenda. With the launch ...
Apr. 28, 2015 11:00 AM EDT Reads: 3,018
The world's leading Cloud event, Cloud Expo has launched Microservices Journal on the SYS-CON.com portal, featuring over 19,000 original articles, news stories, features, and blog entries. DevOps Journal is focused on this critical enterprise IT topic in the world of cloud computing. Microservices Journal offers top articles, news stories, and blog posts from the world's well-known experts and guarantees better exposure for its authors than any other publication. Follow new article posts on T...
Apr. 28, 2015 11:00 AM EDT Reads: 2,228