I've been using WebSockets for a while now, I have chosen to create an Agile project management tool for my final year project at University utilizing Node server and WebSockets. I found using WebSockets provided a 624% increase in the number of requests per second my application could process.
However since starting the project I've read of security loopholes, and some browsers choosing to disable WebSockets by default..
This leads me to the question:
Why use AJAX when WebSockets seems to do such a great job of lowering latency and resource overhead, is there anything that AJAX does better than WebSockets?
WebSockets isn't intended to replace AJAX and is not strictly even a replacement for Comet/long-poll (although there are many cases where this makes sense).
The purpose of WebSockets is to provide a low-latency, bi-directional, full-duplex and long-running connection between a browser and server. WebSockets opens up new application domains to browser applications that were not really possible using HTTP and AJAX (interactive games, dynamic media streams, bridging to existing network protocols, etc).
However, there is certainly an overlap in purpose between WebSockets and AJAX/Comet. For example, when the browser wants to be notified of server events (i.e. push) then Comet techniques and WebSockets are certainly both viable options. If your application needs low-latency push events then this would be a factor in favor of WebSockets. On the other hand, if you need to co-exist with existing frameworks and deployed technologies (OAuth, RESTful APIs, proxies, load balancers) then this would be a factor in favor of Comet techniques (for now).
If you don't need the specific benefits that WebSockets provides, then it's probably a better idea to stick with existing techniques like AJAX and Comet because this allows you to re-use and integrate with a huge existing ecosystem of tools, technologies, security mechanisms, knowledge bases (i.e. far more people on stackoverflow know HTTP/Ajax/Comet than WebSockets), etc.
On the other hand, if you are creating a new application that just doesn't work well within the latency and connection constraints of HTTP/Ajax/Comet, then consider using WebSockets.
Also, some answers indicate that one of the downsides of WebSockets is limited/mixed server and browser support. Let me just diffuse that a bit. While iOS (iPhone, iPad) still supports the older protocol (Hixie) most WebSockets servers support both Hixie and the HyBi/IETF 6455 version. Most other platforms (if they don't already have built-in support) can get WebSockets support via web-socket-js (Flash based polyfill). This covers the vast majority of web users. Also, if you are using Node for the server backend, then consider using Socket.IO which includes web-socket-js as a fallback and if even that is not available (or disabled) then it will fall back to using whatever Comet technique is available for the given browser.
Update: iOS 6 now supports the current HyBi/IETF 6455 standard.
Fast forward to December 2017, Websockets are supported by (practically) every browser and their use is very common.
However, this does not mean that Websockets managed to replace AJAX, at least not completely, especially as HTTP/2 adaptation is on the rise.
The short answer is that AJAX is still great for most REST applications, even when using Websockets. But god is in the details, so...:
AJAX for polling?
The use of AJAX for polling (or long polling) is dying out (and it should be), but it still remains in use for two good reasons (mainly for smaller web apps):
For many developers, AJAX is easier to code, especially when it comes to coding and designing the backend.
With HTTP/2, the highest cost related to AJAX (the establishment of a new connection) was eliminated, allowing AJAX calls to be quite performant, especially for posting and uploading data.
However, Websocket push is far superior to AJAX (no need to re-authenticate or resend headers, no need for "no data" roundtrips, etc'). This was discussed a number of times.
AJAX for REST?
A better use for AJAX is REST API calls. This use simplifies the code base and prevents the Websocket connection from blocking (especially on medium sized data uploads).
There are a number of compelling reasons to prefer AJAX for REST API calls and data uploads:
The AJAX API was practically designed for REST API calls and it's a great fit.
REST calls and uploads using AJAX are significantly easier to code, both on the client and the backend.
As data payload increases, Websocket connections might get blocked unless message fragmentation / multiplexing logic is coded.
If an upload is performed in a single Websocket send call, it could block a Websocket stream until the upload had finished. This will reduce performance, especially on slower clients.
A common design uses small bidi messages transferred over Websockets while REST and data uploads (client to server) leverage AJAX's ease of use to prevent the Websocket from blocking.
However, on larger projects, the flexibility offered by Websockets and the balance between code complexity and resource management will tip the balance in favor of Websockets.
For example, Websocket based uploads could offer the ability to resume large uploads after a connection is dropped and re-established (remember that 5GB movie you wanted to upload?).
By coding upload fragmentation logic, it's easy to resume an interrupted upload (the hard part was coding the thing).
What about HTTP/2 push?
I should probably add that the HTTP/2 push feature doesn't (and probably can't) replace Websockets.
This had been discussed here before, but suffice to mention that a single HTTP/2 connection serves the whole browser (all the tabs/windows), so data being pushed by HTTP/2 doesn't know which tab/window it belongs to, eliminating it's capacity to replace Websocket's ability to push data directly to a specific browser tab / window.
While Websockets are great for small bi-directional data communication, AJAX still carried a number of advantages - especially when considering larger payloads (uploads etc').
And Security?
Well, generally, the more trust and control is offered to a programmer, the more powerful the tool... and the more security concerns that creep up.
AJAX by nature would have the upper hand, since it's security is built in to the browser's code (which is sometimes questionable, but it's still there).
On the other hand, AJAX calls are more susceptible to "man in the middle" attacks, while Websockets security issues are usually bugs in the application code that introduced a security flaw (usually backend authentication logic is where you'll find these).
Personally I don't find this to be that big of a difference, if anything I think Websockets are slightly better off, especially when you know what you're doing.
My Humble Opinion
IMHO, I would use Websockets for everything but REST API calls. Big data uploads I would fragment and send over Websockets when possible.
Polling, IMHO, should be outlawed, the cost in network traffic is horrid and Websocket push is easy enough to manage even for new developers.
In addition to issues with older browsers (including IE9, as WebSockets will be supported starting from IE10), there are still big problems with network intermediaries not yet supporting WebSockets, including transparent proxies, reverse proxies, and load balancers.
There are some mobile carriers that completely block the WebSocket traffic (that is, after the HTTP UPGRADE command).
With years passing, WebSockets will be more and more supported, but in the meantime you should always have an HTTP-based fall-back method for sending data to the browsers.
Most of the complaining I have read about websockets and security is from security vendors of web browser security and firewall security tools. The problem is they don't know how to do security analysis of websockets traffic, because once it has done the upgrade from HTTP to the websocket binary protocol, the packet content and its meaning is application specific (based on whatever you program). This is obviously a logistic nightmare for these companies whose livelihood is based on analyzing and classifying all your internet traffic. :)
WebSockets don't work in older web browsers, and the ones that do support it often have differing implementations. That's pretty much the only good reason why they aren't used all the time in place of AJAX.
I don't think we can do a a clear comparison of Websockets and HTTP as they're no rivals nor solve the same problems.
Websockets are a great choice for handling long-lived bidirectional data streaming in near real-time manner, whereas REST is great for occasional communications. Using websockets is a considerable investment, hence it is an overkill for occasional connections.
You may find that Websockets do better when high loads are present, HTTP is slightly faster in some cases because it can utilise caching. Comparing REST with Websockets is like comparing apples to oranges.
We should be checking which one provides better solution for our application, which one fits best in our use case wins.
An example of the differences between HTTP and Websockets in the form of a client-size lib that can handle Websocket endpoint like REST APIs and RESTful endpoints like Websockets on the client.
https://github.com/mikedeshazer/sockrest
Also, for those who are trying to consume a websocket API on client or vice versa the way they are used to. The libs/sockrest.js pretty much makes it clear the differences (or rather is supposed to).
Related
When using websocket, we need a dedicated connection for bidirectionnel communication. If we use http/2 we have a second connection maintained by the server.
In that case, using websocket seems to introduce an unecessary overhead because with SSE and regular http request we can have the advantage of bidirectionnal communication over a single HTTP/2 connection.
What do you think?
Using 2 streams in one multiplexed HTTP/2 TCP connection (one stream for server-to-client communication - Server Sent Events (SSE), and one stream for client-to-server communication and normal HTTP communication) versus using 2 TCP connections (one for normal HTTP communication and one for WebSocket) is not easy to compare.
Probably the mileage will vary depending on applications.
Overhead ? Well, certainly the number of connections doubles up.
However, WebSocket can compress messages, while SSE cannot.
Flexibility ? If the connections are separated, they can use different encryptions. HTTP/2 typically requires very strong encryption, which may limit performance.
On the other hand, WebSocket does not require TLS.
Does clear-text WebSocket work in mobile networks ? In the experience I have, it depends. Antiviruses, application firewalls, mobile operators may limit WebSocket traffic, or make it less reliable, depending on the country you operate.
API availability ? WebSocket is a wider deployed and recognized standard; for example in Java there is an official API (javax.websocket) and another is coming up (java.net.websocket).
I think SSE is a technically inferior solution for bidirectional web communication and as a technology it did not become very popular (no standard APIs, no books, etc - in comparison with WebSocket).
I would not be surprised if it gets dropped from HTML5, and I would not miss it, despite being one of the first to implement it in Jetty.
Depending on what you are interested in, you have to do your benchmarks or evaluate the technology for your particular case.
From the perspective of a web developer, the difference between Websockets and a REST interface is semantics. REST uses a request/response model where every message from the server is the response to a message from the client. WebSockets, on the other hand, allow both the server and the client to push messages at any time without any relation to a previous request.
Which technique to use depends on what makes more sense in the context of your application. Sure, you can use some tricks to simulate the behavior of one technology with the other, but it is usually preferably to use the one which fits your communication model better when used by-the-book.
Server-sent events are a rather new technology which isn't yet supported by all major browsers, so it is not yet an option for a serious web application.
It depends a lot on what kind of application you want to implement. WebSocket is more suitable if you really need a bidirectional communication between server and client, but you will have to implement all the communication protocol and it might not be well supported by all IT infrastructures (some firewall, proxy or load balancers may not support WebSockets). So if you do not need a 100% bidirectional link, I would advise to use SSE with REST requests for additional information from client to server.
But on the other hand, SSE comes with certain caveats, like for instance in Javascript implementation, you can not overwrite headers. The only solution is to pass query parameters, but then you can face an issue with the query string size limit.
So, again, choosing between SSE and WebSockets really depends on the kind of application you need to implement.
A few months ago, I had written a blog post that may give you some information: http://streamdata.io/blog/push-sse-vs-websockets/. Although at that time we didn't consider HTTP2, this can help know what question you need to ask yourself.
I am redesigning a web application which previously has been rendered server side to a Single Page Application and started to read about websockets . The web application will be using sockets to have new records and/or messages pushed to the client. I have been wondering why most pages which make use of sockets don't handle all their communication over the socket. Most of the times there is RESTful backend in addition to the websocket. Would it be a bad idea to have the client query for new resources over the socket? If so why - other than that a RESTful api might be easier to use with other devices?
I can imagine that using websockets would probably not be the best idea in case the network connection is kind of bad like on mobile devices, but that probably should work quite well with a reasonable connection to the web.
I found this related question, however it is from 2011 and seems a little outdated:
websocket api to replace rest api?
No, it won´t be a bad idea. Actually I work in an application that uses a WebSocket connection for all what is data interaction, the web server only handles requests for resources, views under different languages, dimensions .. etc..
The problem may be the lack of frameworks/tools based on a persistent connection. For many years most of frameworks, front and back end, have been designed and built around the request/response model. The approach shift may be no so easy to accept.
Coming back to this question a few years later, I would like to point out a few aspects to illustrate that having all your communication through websockets does have its drawbacks:
there is no common support for compression. You can easily configure your webserver to compress http requests and browsers have been known to happily accept compressed responses for years, however for web sockets it is still not that easy (even though the situation has improved)
client frameworks often are build upon commonly used standards like rest. The further away you move from frameworks expectations, the less addons or features will be available.
caching in the browser is not as easy. By now this goes a long way, reaching into the realm of offline availability and PWAs.
when using technology, that is only used by a subset of users, it is more likely to find new bugs, or bugs might take longer to fix. And if it's not bugs, there might be an edge case somewhere around the corner. This isn't an issue per se - but something to be aware of. If one runs into those things, they often easily take up quite some time to fix or work around.
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or do Server-Sent Events and WebSocket replace Comet techniques?
I will approach this answer from both a terminology and historical perspective.
As I wrote in this other answer, we can use one of the several umbrella terms to refer to the set of technologies available to asynchronously send events from a web server to a web client (and vice versa). The "Push Technology" term has been used for fifteen years (for a short history of Push Technology you can see this old white paper I wrote many years ago—full disclosure: I am the creator of Lightstreamer). Now, the "Web Streaming" term is gaining consensus among the IT analysts (see Gartner, "Cool Vendors in Application and Integration Platforms, 2012", by Massimo Pezzini and Jess Thompson, 11 April 2012).
The important aspect is that we are talking about Web-based communication, that is, leveraging Web protocols. There are tons of messaging protocols and technologies that are not Web based (most of MOMs, for example) and we do not consider them as part of Push Technology (or Web Streaming).
That being said, you can distinguish between two sub-categories of Push Technology (or Web Streaming):
HTTP based
WebSockets based
Both HTTP and WebSockets are Web protocols.
If you explode the HTTP-based push mechanisms, you can identify:
HTTP Streaming
HTTP Long Polling
HTTP Polling
Traditionally, the "Comet" term (coined in 2006 by Alex Russell) has been referring to both HTTP Streaming and HTTP Polling. But consider that the first implementations of HTTP Streaming go back to 2000, well before the Comet term was coined (examples are Pushlets and Lightstreamer).
Now WebSockets make it simpler to implement Web Streaming, especially for the "backward" channel (messages sent from the browser to the server). For a more detailed explanation on the peculiarities of the backward channel over HTTP, see the final part of this article I wrote for CometDaily: http://cometdaily.com/2011/07/06/push-technology-comet-and-websockets-10-years-of-history-from-lightstreamers-perspective/
As pointed out by Phil, Comet is still necessary and will probably be for some more years, as there are not only old browsers around (including IE9, which does not support WebSockets…) but also infinite pieces of network intermediaries that do not speak WS. For example, we have seen that some mobile carriers in some countries (for example Vodafone Italy) support WSS but block WS. So a world without the Comet "hacks" is still far away… And let me add, on a personal note, that I've never loved the term "hack" applied to Comet (or, from a more correct historical point of view, applied to HTTP Streaming and HTTP Long Polling). Having worked on these techniques for 12 years now, I can say we have been able to refine them so much that they have become a full-blown technology themselves, completely reliable and used every day in many critical production scenarios (in finance, aerospace, and military, to name a few industries).
Now, let's imagine a world where WebSockets are universally supported and Comet is no more necessary. What do you get exactly? Well, just a bi-directional transport, nothing more... On the top of it you need to build everything: a messaging protocol (perhaps based on pub/sub), a server-side interface to talk to your server code, and a good set of optimization techniques and algorithms to manage the data flow, including bandwidth management, data conflation, automatic throttling, delta delivery, etc.
The good thing is that both the messaging protocols and the optimization mechanisms have already been implemented by good Comet solutions. So, extending former Comet servers to support WebSocket is the natural evolution that all of us vendors have implemented.
So, in a nutshell, in a not-so-near future WebSockets might make Comet transports obsolete, but will need to suck in all the higher layers already implemented and well tested on traditional Comet servers.
Comet is a set of technology principles/communication patterns that are typically implemented using HTTP long-poll. It enables a server to send data to the browser on demand (i.e. server push). Current comet implementations require some complex Javascript on the client side and support from the server-side (for long-held requests).
Server-Sent Events is a standard (HTML5) browser API for enabling this sort of on demand server push. You can think of Server-Sent Events as taking what has been done with complex Javascript and pushing it down into the browser itself.
WebSockets allows a browser to establish a persistent full-duplex/bi-directional connection to a server with WebSocket support. It does not require the client to keep making periodic HTTP requests to the server in order to maintain the connection as with AJAX/long-poll. Once the connection is established the overhead per message is very low (a few bytes) compared to the overhead with normal HTTP/HTTP long-poll. You can use WebSockets for efficient server push, but this is just one application.
There are also libraries that build on the AJAX/comet/WebSockets transport layer to provide things like session management, channels, broadcast, pubsub, etc. CometD is an example of this. Another popular example is Socket.IO. Both support WebSockets if it is available for the underlying transport but also support standard AJAX/long-poll if WebSockets is not available.
I initially thought that WebSockets realise Comet. They’re not an alternative. However, after some discussion I was later corrected and convinced by Alex Russell, the creator of "Comet", that this was not the case.
Comet, as #kanaka says, is a set of principles for simulating bi-directional communication between client and server (server push is half of the solution and is now provided by Server-Sent Events and the Event Source API).
However, Comet solutions are hacks because they work inconsistently across web browsers. For that reason Alex Russell says:
Next, are Web Sockets a form of Comet? Or is Comet just the HTTP hacks? I'm gonna go for the latter definition. The phrase and the hacks should probably ride off into the sunset together. I, for one, welcome our non-HTTP realtime overlords. To the extent that we can forget about old browsers (and god know I'm doing my bit: http://google.com/chromeframe), we can all get on board with "Web Sockets" and the need for any particular umbrella goes away.
So lets focus on that: how do we get users into a shiny new browser car? What sort of offer can we make to them about the richness and real-time experiences that an app based on WebSockets can deliver? Comet is about the past. Lets make the future real.
I'm now with Alex on this one. However, Comet - HTTP solutions - aren't going to become obsolete until:
Browser support is 100% and we don't need fallbacks for < IE10. I don't believe that Firefox, Safari, and Opera users are going to be a problem. There may be a small percentage of users that ignore the auto-update prompts for browsers like Firefox but not many.
Anti-virus manufacturers (such as Avast!) start support HTML5 web technologies and stop their software interfering with connectivity.
Some Internet infrastructure is updated to ensure the support of WebSockets. In my experiences connected over WSS over port 443 (a secure WebSocket connection) normally means connections make their way through Firewalls and Proxies but we want WS over port 80 to always be supported too.
While WebSocket does provide at the most fundamental level a way to communicate bi-directionally between a client and a server within the context of the Web and HTTP, it is a simple form of communications.
Comet provides more functionality on top of WebSocket (in fact, cometd even supports websocket), for features:
like publish/subscribe and channels of communications
fallback to older client<->server communications techniques when websocket is unvailable
I thought about getting rid of all client-side Ajax calls (jQuery) and instead use a permanent socket connection (Socket.IO).
Therefore I would use event listeners/emitters client-side and server-side.
Ex. a click event is triggered by user in the browser, client-side emitter pushes the event through socket connection to server. Server-side listener reacts on incoming event, and pushes "done" event back to client. Client's listener reacts on incoming event by fading in DIV element.
Does that make sense at all?
Pros & cons?
There is a lot of common misinformation in this thread that is very inaccurate.
TL/DR;
WebSocket replaces HTTP for applications! It was designed by Google with the help of Microsoft and many other leading companies. All browsers support it. There are no cons.
SocketIO is built on top of the WebSocket protocol (RFC 6455). It was designed to replace AJAX entirely. It does not have scalability issues what-so-ever. It works faster than AJAX while consuming an order of magnitude fewer resources.
AJAX is 10 years old and is built on top of a single JavaScript XMLHTTPRequest function that was added to allow callbacks to servers without reloading the entire page.
In other words, AJAX is a document protocol (HTTP) with a single JavaScript function.
In contrast, WebSocket is a application protocol that was designed to replace HTTP entirely. When you upgrade an HTTP connection (by requesting WebSocket protocol), you enable two-way full duplex communication with the server and no protocol handshaking is involved what so ever. With AJAX, you either must enable keep-alive (which is the same as SocketIO, only older protocol) or, force new HTTP handshakes, which bog down the server, every time you make an AJAX request.
A SocketIO server running on top of Node can handle 100,000 concurrent connections in keep-alive mode using only 4gb of ram and a single CPU, and this limit is caused by the V8 garbage collection engine, not the protocol. You will never, ever achieve this with AJAX, even in your wildest dreams.
Why SocketIO so much faster and consumes so much fewer resources
The main reasons for this is again, WebSocket was designed for applications, and AJAX is a work-around to enable applications on top of a document protocol.
If you dive into the HTTP protocol, and use MVC frameworks, you'll see a single AJAX request will actually transmit 700-900 bytes of protocol load just to AJAX to a URL (without any of your own payload). In striking contrast, WebSocket uses about 10 bytes, or about 70x less data to talk with the server.
Since SocketIO maintains an open connection, there's no handshake, and server response time is limited to round-trip or ping time to the server itself.
There is misinformation that a socket connection is a port connection; it is not. A socket connection is just an entry in a table. Very few resources are consumed, and a single server can provide 1,000,000+ WebSocket connections. An AWS XXL server can and does host 1,000,000+ SocketIO connections.
An AJAX connection will gzip/deflate the entire HTTP headers, decode the headers, encode the headers, and spin up a HTTP server thread to process the request, again, because this is a document protocol; the server was designed to spit out documents a single time.
In contrast, WebSocket simply stores an entry in a table for a connection, approximately 40-80 bytes. That's literally it. No polling occurs, at all.
WebSocket was designed to scale.
As far as SocketIO being messy... This is not the case at all. AJAX is messy, you need promise/response.
With SocketIO, you simply have emitters and receivers; they don't even need to know about each-other; no promise system is needed:
To request a list of users you simply send the server a message...
socket.emit("giveMeTheUsers");
When the server is ready, it will send you back another message. Tada, you're done. So, to process a list of users you simply say what to do when you get a response you're looking for...
socket.on("HereAreTheUsers", showUsers(data) );
That's it. Where is the mess? Well, there is none :) Separation of concerns? Done for you. Locking the client so they know they have to wait? They don't have to wait :) You could get a new list of users whenever... The server could even play back any UI command this way... Clients can connect to each other without even using a server with WebRTC...
Chat system in SocketIO? 10 lines of code. Real-time video conferencing? 80 lines of code Yes... Luke... Join me. use the right protocol for the job... If you're writing an app... use an app protocol.
I think the problem and confusion here is coming from people that are used to using AJAX and thinking they need all the extra promise protocol on the client and a REST API on the back end... Well you don't. :) It's not needed anymore :)
yes, you read that right... a REST API is not needed anymore when you decide to switch to WebSocket. REST is actually outdated. if you write a desktop app, do you communicate with the dialog with REST? No :) That's pretty dumb.
SocketIO, utilizing WebSocket does the same thing for you... you can start to think of the client-side as simple the dialog for your app. You no longer need REST, at all.
In fact, if you try to use REST while using WebSocket, it's just as silly as using REST as the communication protocol for a desktop dialog... there is absolutely no point, at all.
What's that you say Timmy? What about other apps that want to use your app? You should give them access to REST? Timmy... WebSocket has been out for 4 years... Just have them connect to your app using WebSocket, and let them request the messages using that protocol... it will consume 50x fewer resources, be much faster, and 10x easier to develop... Why support the past when you're creating the future?
Sure, there are use cases for REST, but they are all for older and outdated systems... Most people just don't know it yet.
UPDATE:
A LOT of people have been asking me recently how can they start writing an app in 2018 (and now soon 2019) using WebSockets, that the barrier seems really high, that once they play with Socket.IO they don't know where else to turn or what to learn.
Fortunately the last 3 years have been very kind to WebSockets...
There are now 3 major frameworks that support BOTH REST and WebSocket, and even IoT protocols or other minimal/speedy protocols like ZeroMQ, and you don't have to worry about any of it; you just get support for it out of the box.
Note: Although Meteor is by far the most popular, I am leaving it out because although they are a very, very well-funded WebSocket framework, anyone who has coded with Meteor for a few years will tell you, it's an internal mess and a nightmare to scale. Sort of like WordPress is to PHP, it is there, it is popular, but it is not very well made. It's not well-thought out, and it will soon die. Sorry Meteor folks, but check out these 3 other projects compared to Meteor, and you will throw Meteor away the same day :)
With all of the below frameworks, you write your service once, and you get both REST and WebSocket support. What's more, it's a single line of config code to swap between almost any backend database.
Feathers Easiest to use, works the same on the front and backend, and supports most features, Feathers is a collection of light-weight wrappers for existing tools like express. Using awesome tools like feathers-vuex, you can create immutable services that are fully mockable, support REST, WebSocket and other protocols (using Primus), and get free full CRUD operations, including search and pagination, without a single line of code (just some config). Also works really great with generated data like json-schema-faker so you can not only fully mock things, you can mock it with random yet valid data. You can wire up an app to support type-ahead search, create, delete and edit, with no code (just config). As some of you may know, proper code-through-config is the biggest barrier to self-modifying code. Feathers does it right, and will push you towards the front of the pack in the future of app design.
Moleculer Moleculer is unfortunately an order of magnitude better at the backend than Feathers. While feathers will work, and let you scale to infinity, feathers simply doesn't even begin to think about things like production clustering, live server consoles, fault tolerance, piping logs out of the box, or API Gateways (while I've built a production API gateway out of Feathers, Moleculer does it way, way better). Moleculer is also the fastest growing, both in popularity and new features, than any WebSocket framework.
The winning strike with Moleculer is you can use a Feathers or ActionHero front-end with a Moleculer backend, and although you lose some generators, you gain a lot of production quality.
Because of this I recommend learning Feathers on the front and backend, and once you make your first app, try switching your backend to Moleculer. Moleculer is harder to get started with, but only because it solves all the scaling problems for you, and this information can confuse newer users.
ActionHero Listed here as a viable alternative, but Feathers and Moleculer are better implementations. If anything about ActionHero doesn't Jive with you, don't use it; there are two better ways above that give you more, faster.
NOTE: API Gateways are the future, and all 3 of the above support them, but Moleculer literally gives you it out of the box. An API gateway lets you massage your client interaction, allowing caching, memoization, client-to-client messaging, blacklisting, registration, fault tolerance and all other scaling issues to be handled by a single platform component. Coupling your API Gateway with Kubernetes will let you scale to infinity with the least amount of problems possible. It is the best design method available for scalable apps.
Update for 2021:
The industry has evolved so much that you don't even need to pay attention to the protocol. GraphQL now uses WebSockets by default! Just look up how to use subscriptions, and you're done. The fastest way to handle it will occur for you.
If you use Vue, React or Angular, you're in luck, because there is a native GraphQL implementation for you! Just call your data from the server using a GraphQL subscription, and that data object will stay up to date and reactive on it's own.
GraphQL will even fall-back to REST for you when you need to use legacy systems, and subscriptions will still update using sockets. Everything is solved when you move to GraphQL.
Yes, if you thought "WTH?!?" when you heard you can simply subscribe, like with FireBase, to a server object, and it will update itself for you. Yes. That's now true. Just use a GraphQL subscription. It will use WebSockets.
Chat system? 1 line of code.
Real time video system? 1 line of code.
Video game with 10mb of open world data shared across 1m real-time users? 1 line of code. The code is just your GQL query now.
As long as you build or use the right back-end, all this realtime stuff is now done for you with GQL subscriptions. Make the switch as soon as you can and stop worrying about protocols.
Socket.IO uses persistent connection between client and server, so you will reach a maximum limit of concurrent connections depending on the resources you have on server side, while more Ajax async requests can be served with the same resources.
Socket.IO is mainly designed for realtime and bi-directional connections between client and server and in some applications there is no need to keep permanent connections. On the other hand Ajax async connections should pass the HTTP connection setup phase and send header data and all cookies with every request.
Socket.IO has been designed as a single process server and may have scalability issues depending server resources that you are bound to.
Socket.IO in not well suited for applications when you are better to cache results of client requests.
Socket.IO applications face with difficulties with SEO optimization and search engine indexing.
Socket.IO is not a standard and not equivalent to W3C Web Socket API, It uses current Web Socket API if browser supports, socket.io created by a person to resolve cross browser compatibility in real time apps and is so young, about 1 year old. Its learning curve, less developers and community resources compared with ajax/jquery, long term maintenance and less need or better options in future may be important for developer teams to make their code based on socket.io or not.
Sending one way messages and invoking callbacks to them can get very messy.
$.get('/api', sendData, returnFunction); is cleaner than
socket.emit('sendApi', sendData); socket.on('receiveApi', returnFunction);
Which is why dnode and nowjs were built on top of socket.io to make things manageable. Still event driven but without giving up callbacks.
I'm working on the design of a web app which will be using AJAX to communicate with a server on an embedded device. But for one feature, the client will need to get very frequent updates (>10 per second), as close to real time as possible, for an extended period of time. Meanwhile typical AJAX requests will need to be handled from time to time.
Some considerations unique to this project:
This data will be very small, probably no more than a single numeric value.
There will only be 1 client connected to the server at a time, so scaling is not an issue.
The client and server will reside on the same local network, so the connection will be fast and reliable.
The app will be designed for Android devices, so we can take advantage of any platform-specific browser features.
The backend will most likely be implemented in Python using WSGI on Apache or lighttpd, but that is still open for discussion.
I'm looking into Comet techniques including XHL long polling and hidden iframe but I'm pretty new to web development and I don't know what kind of performance we can expect. The server shouldn't have any problem preparing the data, it's just a matter of pushing it out to the client as quickly as possible. Is 10 updates per second an unreasonable expectation for any of the Comet techniques, or even regular AJAX polling? Or is there another method you would suggest?
I realize this is ultimately going to take some prototyping, but if someone can give me a ball-park estimate or better yet specific technologies (client and server side) that would provide the best performance in this case, that would be a great help.
You may want to consider WebSockets. That way you wouldn't have to poll, you would receive data directly from your server. I'm not sure what server implementations are available at this point since it's still a pretty new technology, but I found a blog post about a library for WebSockets on Android:
http://anismiles.wordpress.com/2011/02/03/websocket-support-in-android%E2%80%99s-phonegap-apps/
For a Python back end, you might want to look into Twisted. I would also recommend the WebSocket approach, but failing that, and since you seem to be focused on a browser client, I would default to HTTP Streaming rather than polling or long-polls. This jQuery Plugin implements an http streaming Ajax client and claims specifically to support Twisted.
I am not sure if this would be helpful at all but you may want to try Comet style ajax
http://ajaxian.com/archives/comet-a-new-approach-to-ajax-applications