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I am learning about REST API and I am unable to understand how REST is used in distributed web application?
This is the only reference i have seen. But still I am unable to learn about REST for distributed computing.
Thank You in advance.
It isn’t really clear to me, what you are asking with your question, but generally - REST is just another way to do RMI (Remote Method Invocation) or RPC (Remote Procedure Call). However, while RMI works only within Java, REST uses the HTTP Protocol to for communication. Since HTTP is implemented in most of the technologies / libraries / languages we use today, it is an easy way to connect them.
Originally SOAP (Simple Object Access Protocol) was used to implement inter server and client-server communications. SOAP has many additional features on top of HTTP. The WSDL (Web Services Description Language) allows for automatic proxy generation, for instance. While those features make SOAP rich and perfect fit for Enterprise applications (CERN implemented their own version of SOAP which allowed state-full communication), it was also too bulky for many, quickly changing, smaller companies.
REST uses features from HTTP but can basically vary in many ways. The url's and the objects can be defined freely, as well as the format in which objects are serialised (mostly JSON). This feature paired with dynamic languages like Python, Ruby or JavaScript (Client, or NodeJS) makes it very easy to set up communication between different services as well as client and service (SPA - Single Page Application, for the later).
However, I think the very interesting fact is, that people discovered, you have to pay a high price for this elasticity:
JSON represented objects - although smaller than XML - are still larger than byte-code (this can be solved to a large part by gzip, but creates a second problem)
Serialising and Deserialising object to/from strings is very inefficient und much slower than byte-code representations. (And of course zipping the strings to reduce size also costs CPU)
So far there was the choice - HTTP, which is inefficient, or RMI, which is inflexible and can be used only by few languages. This is why there are two projects to solve this:
Protocol Buffers from Google https://code.google.com/p/protobuf/
Apache Thrift http://thrift.apache.org/
Both of those projects allow you to use a specific binary format, to you and your messages. And because both projects have implementations in different languages (Apache Thrift many more than Google's Protocol Buffer) you can use this format to communicate between different servers.
Also a direct end-to-end communication is not always what you want, which is, why there are different Messaging Queues which can fulfil many tasks additionally to message forwarding (for instance publish-subscribe, round robin delivery to a set of services, ...) The probably most widely used one is ZeroMQ.
Conclusion
You can use REST to communicate between different services in your distributed web applications. And this is also often used, due to the simplicity of implementing such a communication channel between many different hosts and technologies. However the overhead in serialising / deserialising can cost you a lot of CPU-Time, especially if you have a large backend infrastructure with many services. This is why you should rather choose one of the binary formats (Apache Thrift, Protocol Buffers), to ensure efficiency.
Related
I want to dive into the whole diversity of tools which provide connection between programs over the network.
To clarify the question, I divide it on subquestions:
Why some groups of programs (or specific tools/frameworks/approaches with programming languages where this frameworks can be used) were popular in each period of time? (I expect description of problems which were solved, description of tools, why those tools are considered as best solution to those problems at that time, why some tools lost popularity)
What is the entire history of software communication over the network? (tools/approaches popularity precisely to decades)
What are the modern solutions to this problem?
I can distinguish only two significant approaches.
RPC, RMI and their implementations (I saw this, but it is about concrete problem and specific tools to solve this problem, I want to see the place of this problem in the whole picture of interconnection programs over the network. I heard about implementations: ONC RPC, XML-RPC, CORBA, DCOM, gRPC, but which are active now? which are reasonable to use? which are preferable and why? I want answers not to be opinion based, so I accept answers like "technology A better than technology B for problem X because ..." only if there is reliable research/statistics or facts). I heard that RPC and RMI were popular 10 years ago. Are they still?
Web services: REST, SOAP.
Am I miss something? Maybe there are some technologies which solve problem completely new way? Maybe there are technologies which can be treated as replacement to RPC(RMI) and Web Services? Can we replace RPC(RMI) by REST for any task? Can we replace RPC(RMI) by REST only for modern tasks? Should I separate technologies not as RPC and Web Services, but in some other manner?
As a partial answer, I can give you my feedback on the use of RabbitMQ.
As explain here, it provides a lot of different ways to use it :
RPC by implementing a "callback" queue
One to one, one to many routing strategy to propagate your events through your whole infrastructure and target the right destination.
It comes with the ability to persist messages to avoid loosing data when a crash appears but also with some plugins to increase possibilities (e.g x-delayed plugin)
This technologie written in Erlang is powerful and is a must try in term of communication between programs.
To your question „Am I missing something“: yes.
Very popular communication patterns are the so-called Event-Driven or Message-Driven protocols. This type of protocols are often used in distributed systems such web applications, microservices and IoT-Environments. The communication is complete asynchronously and allows building scalable and loosely coupled systems.
There are many different frameworks and methods for Event-Driven systems like WebSockets, WebHooks, Pub-Sub and Messaging-Librarys like AcitveMQ, OpenMQ, RabbitMQ, ZeroMQ and MQTT.
Hope this info helps for your research.
I have been reading on difference between REST and SOAP. I see in many posts that SOAP is a better choice for distributed transactional resources.
Please give me a practical example of SOAP being used for distributed transaction.
SOAP has been the main player for many years inside enterprise applications simply because there was no alternative. REST came later.
Since SOAP is a protocol it is easier to build tools around it since you know how it behaves always (i.e. as the protocol is defined). For this reason and because it's mature as technology, a lot of other specifications were build around it, to cover any uses one might have for doing something with SOAP. See a list here. There are of course some for transactional semantics also. If you use
SOAP with a technology like Java or C# (which are heavyweight champions in the enterprise applications field) then you can have these transactional specifications already implemented in the framework or libraries and you just use them.
REST on the other hand is an architectural style of building applications. It's harder to limit it to a set of specifications. You can implement it in many ways. It is also going somehow against "the way of the SOAP" by staying away of creating new standards or specifications and instead just reusing the ones of the web. For this reason, there are no specs or tools to help you with transactional RESTful services. You have to build your own.
So when your application is build by self-contained web services, and these services need to cooperate on creating the applications outcome, and you need a distributed transaction to guarantee that outcome is consistent (all operations succeeding or none succeeding) then it's (more) practical to go for the technology that has the better tooling in supporting it.
I am currently doing my research on building a chat system with more than 10k users connected online. I came across technologies and ways to do it such as jabber(XMPP), websockets, long polling, push. As far as I now, long polling might not work given the number of users. I know there is a lot of ways to accomplish this. I also know that facebook and Google chat systems are developed on XMPP.
I would truly appreciate if anyone could point me to the right direction. I believe all these methods and technologies out there are good depending on the scale of the project. I definitely need performance and scalability.
I've used Socket.io together with NodeJS for such a chat application. It scaled to over 10K concurrent users on moderate servers and there was a lot of room to grow.
This does depend on your limitations, tho.
What kind of hardware are you planning on using?
Which operating system would power your servers?
Which client platforms are you targeting?
Do you have an existing infrastructure you need to fit this into?
Do you have a previously selected programming language?
The existing skill sets your team members have and your team's ability to adopt new platforms and languages if necessary.
Take all of the above into consideration when making your decision.
Personally, I've found XMPP to be quite adequate, but a bit bloated for my purposes. YMMV.
You are comparing a fruit basket and three different variety of oranges.
XMPP is the only protocol that you have mentioned that actually is designed to support a chat system (of which many exist). The others are simply asynchronous messaging protocols/techniques. XMPP already supports http based chat via BOSH. Without a doubt, it will also support WebSockets when the specification is finalized. There is actually a draft of this already written, but at this point it appears to be a draft using a draft, so there will probably be few, if any, implementations.
Using XMPP would allow you to build on a proven technology for implementing a chat system and would allow you to choose what transport you want to use "under the hood". You haven't actually said whether you need a http based transport or not, but with XMPP you can use the stock tcp socket based transport or a http based one (BOSH) with the knowledge that it will also support WebSockets in the future.
The other benefit is of course that this is a widely used standard that will allow reuse of existing clients, servers and libraries in pretty much all popular (and not so popular) languages and platforms.
Scalability is not too much of a concern with the numbers you are quoting, as most (maybe all) existing xmpp servers will handle that many users.
I've recently decided to take on a pretty big software engineering project that will involve developing a client-server based application. My plan is to develop as many clients as possible: including native iPhone, Android and Blackberry Apps as well as a web-based app.
For my server I'm planning on using a VPS (possibly from slicehost.com) running a flavor of Linux with a MySQL database. My first question is what should be my strategy for clients to interface with the server. My ideas are:
HTTP-POST or GET based communication with a PHP script.
This is something I'm very familiar with - passing information to a PHP script from a form, working with it and returning output. I'm assuming I'd want to return output to clients as some sort of XML or JSON based string. I'm also assuming I'd want to create a well defined API for clients that want to interface with my server.
Socket based communication with either a PHP script, Java program, or C++ program
This I'm less familiar with. I've worked with basic tutorials on creating a script or simple application that creates a socket, listens for a connection and returns data. I'm assuming there is far less communication data-overhead with this method than an HTTP based method. My dream is for there to be A LOT of concurrent clients in use, all working with the server/database. I'm not sure if a simple HTTP/PHP script based communication design can scale effectively to meet the needs of many clients. Also, I may eventually want the capability of a Server-Push to clients triggered by various server events. I'm also unsure of what programming language is best suited for this. If efficiency is a big concern I'd imagine a PHP script might not be efficient enough?
Is there a commonly accepted way of doing this? For me this is an attempt to bridge a gap between some of my current skills. I have a lot of experience with PHP and interfacing with a MySQl database to serve dynamic web pages. I also have a lot of experience developing native iPhone applications (however none that have had any significant server-based communication). Also I've worked with Java/C++, and I've developed applications in both languages that have interfaced with MySQL.
I don't anticipate my clients sending/receiving a tremendous amount of data to/from a server. Something on par with a set of strings per a given client-side event.
Another question: Using a VPS - good idea? I obviously don't want to pay for a full-dedicated server (slicehost offers a VPS starting at ~ $20/month), and I'm assuming a VPS will be capable of meeting the requirements of a few initial clients. As more and more users begin to interface with my server, I'm assuming it will be possible to migrate to larger and larger 'slices' and possibly eventually moving to a full-dedicated server if necessary.
Thanks for the advice! :)
I'd say go with the simplicity of HTTP, at least until your needs outgrow its capabilities. (The more stateful your application needs to be, the less HTTP fits).
For low cost and scalability, you probably can't go wrong with a cloud like Rackspace's or Amazon's. But I'm just getting started with those, my servers have been VPSs from tektonic until now.
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I'm looking for some guidance/books to read when it comes to creating a software requirement specification for a web application. For inspiration I have read some spec documents for desktop based applications. The documents I have read capture a systems functional requirements in use cases which tend to be rather data oriented with use cases centered around the various CRUD operations the application is intended to perform.
I like this structure however I'm finding it rather difficult to marry it to what my web application needs to do, mostly reading data as opposed to manipulating it. I've had a go at writing some use cases however they all tend to boil down to "Search for item", "Change view of search results" or "User selects facet to refine search results". This doesn't sound quite right to me and makes me wonder if I'm going about this the right way.
Are there planning differences between web based and desktop based applications?
In my experience, there is really nothing wrong as having all the specifications being CRUD. Most of the time, any application isn't just "a simple CRUD app." Requirements evolve and different parts of the systems tend to diverge and acquire some specific logic.
Even if it feels like repeating the same CRUD sentences over and over, actually writing them down and thinking about it (instead of copy & pasting) will often uncover hidden requirements.
The differences between desktop based applications and web based applications is staggering.
I recommend reading these in exactly this order and apply this knowledge in exactly the opposite order, aside from CSS 3, HTML 5, and XHTML 1.1:
RFC 3986 - URI
RFC 2616 - HTTP 1.1
RFC 4346 - TLS 1.1
RFC 4251 - SSH Protocol
RFC 4252 - SSH Authentication
RFC 4253 - SSH Transport
RFC 2045 - MIME
RFC 4627 - JSON
HTML 4.01
XML
XHTML 1.0
XHTML 1.1
ECMAScript
CSS 2
HTML 5 (Not a standard)
CSS 3 (Not a standard)
Web Content Accessibility Guidelines 2.0
Symantec Internet Security Threat Report Volume XIV
Symantec Internet Security Threat Report Volume XV
OWASP Top 10
SEO
Once you have finished reading this you should begin to understand how the basic technology of the web works. Only at this point would you be ready to develop, conformantly, for a web application. There are many other technologies at play, but these are the basics and once you are familiar with the basics you will know where else to look for more information.
Basically you can sue the same method as for desktop applications, although you might make some addition, because we applications often tend to have different type of requrements. First of all, read something good about Use Cases, there are different use case levels and that might be a solution to your use cases which do not seem so right. Also do not forget about use case generalization and parametrized use cases if CRUD repetition is the problem. One thing, which is often more important in web applications than in desktop apps is the aspect of usability. This is because of the nature of the web - people have ofthe the coice of not using your service and go to next google result if you app is not usable. So what I think is a good addition to the spec are Personas - just find some possible instances of the human actors for your use cases and try to think of some goals they might want to achieve often using your web app and present how they will achieve them using your web app (and try to make it super easy of course). Another important thing is the Information Architecture - the way in which you will provide information in your web app. This comprises of navigation, some basic layout, but not necessarily design, just information about where to find something in your web app. This can be done using some rapid prototyping tools.