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Can Angular views and html use HTTP whilst JSON RestAPI calls use HTTPS?

Thinking about HTTPS, it is a compute-intensive protocol and one should only use it where necessary. I'm working on a web application and I will be using Angular.js MVC on the client side, calling into WebAPI REST Api returning JSON.
When I think about it I do not need to encrypt the HTML, the client-side javascript or styles sheet etc. After initial handshake only the data calls to the REST Api need encrypting.
Do other people do this? Are there any pitfalls or caveats?

Here's a great Mozilla article detailing their restrictions and why they exist.
Their recommendation is to always stick strictly to either HTTP or HTTPS.
Also, I suspect that browsers and web servers will greatly minimize the impact of encrypting the data over ssl on subsequent calls. I suspect if you profile it you'll find the impact minimal/non-measurable.

Call ajax when value is inserted on database [duplicate]

Of course I am aware of Ajax, but the problem with Ajax is that the browser should poll the server frequently to find whether there is new data. This increases server load.
Is there any better method (even using Ajax) other than polling the server frequently?

Yes, what you're looking for is COMET http://en.wikipedia.org/wiki/Comet_(programming). Other good Google terms to search for are AJAX-push and reverse-ajax.

Yes, it's called Reverse Ajax or Comet. Comet is basically an umbrella term for different ways of opening long-lived HTTP requests in order to push data in real-time to a web browser. I'd recommend StreamHub Push Server, they have some cool demos and it's much easier to get started with than any of the other servers. Check out the Getting Started with Comet and StreamHub Tutorial for a quick intro. You can use the Community Edition which is available to download for free but is limited to 20 concurrent users. The commercial version is well worth it for the support alone plus you get SSL and Desktop .NET & Java client adapters. Help is available via the Google Group, there's a good bunch of tutorials on the net and there's a GWT Comet adapter too.

Nowadays you should use WebSockets.
This is 2011 standard that allows to initiate connections with HTTP and then upgrade them to two-directional client-server message-based communication.
You can easily initiate the connection from javascript:
var ws = new WebSocket("ws://your.domain.com/somePathIfYouNeed?args=any");
ws.onmessage = function (evt)
{
var message = evt.data;
//decode message (with JSON or something) and do the needed
};
The sever-side handling depend on your tenchnology stack.

Look into Comet (a spoof on the fact that Ajax is a cleaning agent and so is Comet) which is basically "reverse Ajax." Be aware that this requires a long-lived server connection for each user to receive notifications so be aware of the performance implications when writing your app.
http://en.wikipedia.org/wiki/Comet_(programming)

Comet is definitely what you want. Depending on your language/framework requirements, there are different server libraries available. For example, WebSync is an IIS-integrated comet server for ASP.NET/C#/IIS developers, and there are a bunch of other standalone servers as well if you need tighter integration with other languages.

I would strongly suggest to invest some time on Comet, but I dont know an actual implementation or library you could use.
For an sort of "callcenter control panel" of a web app that involved updating agent and call-queue status for a live Callcenter we developed an in-house solution that works, but is far away from a library you could use.
What we did was to implement a small service on the server that talks to the phone-system, waits for new events and maintains a photograph of the situation. This service provides a small webserver.
Our web-clients connects over HTTP to this webserver and ask for the last photo (coded in XML), displays it and then goes again, asking for the new photo. The webserver at this point can:
Return the new photo, if there is one
Block the client for some seconds (30 in our setup) waiting for some event to ocurr and change the photograph. If no event was generated at that point, it returns the same photo, only to allow the connection to stay alive and not timeout the client.
This way, when clients polls, it get a response in 0 to 30 seconds max. If a new event was already generated it gets it immediately), otherwise it blocks until new event is generated.
It's basically polling, but it somewhat smart polling to not overheat the webserver. If Comet is not your answer, I'm sure this could be implemented using the same idea but using more extensively AJAX or coding in JSON for better results. This was designed pre-AJAX era, so there are lots of room for improvement.
If someone can provide a actual lightweight implementation of this, great!

An interesting alternative to Comet is to use sockets in Flash.

Yet another, standard, way is SSE (Server-Sent Events, also known as EventSource, after the JavaScript object).

Comet was actually coined by Alex Russell from Dojo Toolkit ( http://www.dojotoolkit.org ). Here is a link to more infomration http://cometdproject.dojotoolkit.org/

There are other methods. Not sure if they are "better" in your situation. You could have a Java applet that connects to the server on page load and waits for stuff to be sent by the server. It would be a quite a bit slower on start-up, but would allow the browser to receive data from the server on an infrequent basis, without polling.

You can use a Flash/Flex application on the client with BlazeDS or LiveCycle on the server side. Data can be pushed to the client using an RTMP connection. Be aware that RTMP uses a non standard port. But you can easily fall back to polling if the port is blocked.

It's possible to achive what you're aiming at through the use of persistent http connections.
Check out the Comet article over at wikipedia, that's a good place to start.
You're not providing much info but if you're looking at building some kind of event-driven site (a'la digg spy) or something along the lines of that you'll probably be looking at implementing a hidden IFRAME that connects to a url where the connection never closes and then you'll push script-tags from the server to the client in order to perform the updates.

Might be worth checking out Meteor Server which is a web server designed for COMET. Nice demo and it also is used by twitterfall.

Once a connection is opened to the server it can be kept open and the server can Push content a long while ago I did with using multipart/x-mixed-replace but this didn't work in IE.
I think you can do clever stuff with polling that makes it work more like push by not sending content unchanged headers but leaving the connection open but I've never done this.

You could try out our Comet Component - though it's extremely experimental...!

please check this library https://github.com/SignalR/SignalR to know how to push data to clients dynamically as it becomes available

You can also look into Java Pushlets if you are using jsp pages.

Might want to look at ReverseHTTP also.

How does WebSockets scale compared to standard HTTP?

How does a site programmed using TCP (that is, someone on the site is connected to the server and exchanging information via TCP) scales compared to just serving information via AJAX? Say the information exchanged is the same.
Trying to clarify: I'm asking specifially about scale: I've read that keeping thousands of TCP connections is resources (which?) demanding, as compared to just serving information statically. I want to know if this correct.

WebSockets is a technology that allows the server to push notifications to the client. AJAX on the other hand is a pull technology meaning that the client is sending requests to the server.
So for example if you had an application which needed to receive notifications from the server at regular intervals and update its UI, WebSocket is more adapted and much better. With AJAX you will have to hammer your server with requests at regular intervals to see whether some state changed on the server. With WebSockets, it's the server that will notify the client for some event happening on the server. And this will happen in a single request.
So I guess it would really depend on the type of application you are developing but WebSockets and AJAX are two completely different technologies solving different kind of problems. Which one to choose would depend on your scenario.

Websockets are not a one-for-one with AJAX; they offer substantially different features. Websockets offers the ability to 'push' data to the client. AJAX works by 'pushing' data and returning a response.
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 possibilities with browser applications that were previously unavailable using HTTP or AJAX.
However, there is certainly an overlap in purpose between WebSockets and AJAX. For example, when the browser wants to be notified of server events (i.e. push) either AJAX or WebSockets are both viable options. If your application needs low-latency push events then this would be a factor in favor of WebSockets which would definitely scale better in this scenario. On the other hand, if you need to work with existing frameworks and deployed technologies (OAuth, RESTful API's, proxies, etc.) then AJAX is preferable.
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 because this allows you to re-use and integrate with an existing ecosystem of tools, technologies, security mechanisms, knowledge bases that have been developed over the last 7 years.
But overall, Websockets will outperform AJAX by a significant factor.

I don't think there's any difference when it comes to scalability between WebSockets and standards TCP connnections. WebSocket is an upgrade from a static one way pipe into a duplex one. The physical resources are the exact same.
The main advantage of WebSockets is that they run over port 80, so it avoids most firewall problems, but you have to first connect over standard HTTP.

Here's a good page that clearly shows the benefits of the WebSocket API compared to Ajax long polling (especially on a large scale): http://www.websocket.org/quantum.html
It basically comes down to the fact that once the initial HTTP handshake is established, data can go back and forth much more quickly because the header overhead is greatly reduced (this is what most people refer to as bidirectional communication).
As an off note, if you only need to be able to push data from the server on a regular basis, but you don't need to make many client-initiated requests, then using HTML5 server-sent events with occasional Ajax requests from the client might be just what you need and much easier to implement then the WebSocket API.

Ajax simple question

I have a very simple question about ajax.
If I'd like to refresh a particular area of my site I supose ajax would be the best way.
But is there anyway instead of having a javascript periodically checking for changes on the server, the server would send the data when a given event would happen?
What I'd like was the client not needing to send requests periodically but instead the server would only send the info to the client which in turn would have some kind of event listener.
Thanks in advance

Yes, this can be done. It is referred to as "push" or "push streaming".
Here is one website that offers the ability to do this: InstantPush. And a brief quote from their home page:
"InstantPush is used to make web pages
and mobile phones go live. They will
instantly be updated in real time when
a change occurs at the server side.
Standard web communication makes
updates pass firewalls and proxies.
Without any modules at the client
side!
InstantPush has been used since 2001,
before "Ajax was invented". It is
probably the First Ajax Push
Framework.
InstantPush is leading the market in
northern Europe."
Here is another company offering this technology: LightStreamer. And a quote from their home page:
"Lightstreamer is a scalable and reliable Server for pushing live data to Rich Internet Applications
Based on the Comet and Real-Time Web
paradigms, it streams real-time data
to any Web browser and client
application. HTML, HTML5, AJAX, Flex,
Silverlight, Java, .NET, iOS, Android,
and BlackBerry applications, can
easily receive live data from
Lightstreamer Server.
Lightstreamer has been used in many
mission-critical production systems,
where scalability, low network impact,
bandwidth management, adaptive
streaming, and other advanced
features, have proven fundamental."

This cannot be done because the http protocol works by sending a request and receiving a response from the server, hence the server cannot a response without receiving a request.

No this cannot be done. A server's job is to serve up results from a request, one that it must have to begin with.

That is not possible using traditional HTTP. You can, however, use long polling or one of its siblings to simulate push behaviour.

I think that websockets is the way to go, but is not supported for all browsers yet.
I used them with ruby and chrome and was pretty easy.

this is indeed a difficult ask where server broadcasts/pushes data to clients without being requested. HTTP is stateless and even if browser is a registered client, it still needs to request either through code or through some tags like meta refresh. New but still not so stable options are Comet or websockets.
Answer is Comet rather than websockets. YES, it is possible.
Another way is using Browser plugin.
This is an except from wiki page at Push Technology
* Apple Push Notification Service
* BOSH
* Comet
* Client–server model
* File transfer
* Pull technology
* Push Access Protocol
* Push e-mail
* Reverse Ajax
* Streaming media
* WebSockets

Live Connection from Javascript/html

Is there a way to have a live connection (like for a chat server) with a server using only HTML(5)/JavaScript?

Apparently FF4, Chrome, and Safari all support Web Sockets.
Here's a firefox example, although I'm not sure the spec is completely finalized yet.

Due to the nature of HTTP (only clients can start requests), you would need a "Push" server (aka Comet) on the server-side. You'd still only need JS on the client. See:
HTTP Streaming for an explanation of the technology
APE: Ajax Push Engine for usable implementation
Comet Daily for news on Comet
This can also be implemented with a periodic refresh (polling) if you can't install a Comet engine on the server.

Yup. AJAX and some server code to handle messages updates is all you need to create just such a system. As #NullUserException noted, something like Comet might make this easier.