Phil Leggetter - Software Consultant » comet

Using real-time web software and technology to distribute events

Phil Leggetter — Sat, 27 Feb 2010 11:08:36 +0000

I’ve just come across William Vambenepe’s blog and an article called “Waiting for events (in Cloud APIs)“ where he discusses how an event system is missing from cloud vendor APIs.

With my interest in Comet I straight away thought of this as a solution to the notification requirement and it’s interesting that the article goes on to talk about subscription management and then moves on to thinking about the delivery mechanism which are all key aspects of a good comet implementation:

How do you deliver notifications? Do you keep HTTP connections open through tricks similar to how self-updating web pages work (e.g. COMET, long polling and soon WebSockets)? Or do you just provide a listener endpoint to which the notifier tries to connect (which, in the case of public cloud deployments, means you need to have a publicly-addressable listener, but hopefully not on the same Cloud infrastructure). Do you use XMPP? AMQP? Email? Can I have you hold my events and let me come pull them?

However, when considering a notification system such as this you need to consider how frequently events would actually occur. How often would a new virtual machine in the cloud be spun up? How frequently do virtual machines unexpectedly crash? In relation to events in other scenarios such as stock rate updates or events within the Premier League between 15:00 and 17:00 on a Saturday, probably not all that frequently.

You also need to think about what would be consuming the event. Would it be an application with a user interface that prompts the user to take action or would it be an application with built in logic to handle a virtual machine failure event? If the application is running on a server then there is no reason why that server couldn’t be informed of the event via a single call to a web service, or maybe using something such as PUbSubHubbub, rather than holding open a connection to the cloud API – William describes this as a “listener endpoint”. If the application consuming the event is a web application, maybe the application is the cloud vendors VM dashboard, then Comet would be an ideal choice for instant notification.

Frequency of events and the event consuming application are two key things to consider when thinking about the best way to distribute and consume events using real-time web technologies. As an event-based API developer you may need to consider distributing your events in a number of ways to give application developers the choice.

Are there any notification systems out there that can be used by an API developer to easily distribute events in either way?

Why Comet is key to the Truly Real-Time Web

Phil Leggetter — Sat, 14 Nov 2009 21:01:57 +0000

A lot of websites use HTTP Polling to update data on on their website or application without the need for the user refreshing the website. This is clearly better than a purely static page, but during the time between each poll the data on the page has the potential of being out of date (stale) so to make a decision based on the information on a potentially stale page can be a risky one.

The normal example given to show the benefits of using Comet to achieve full HTTP streaming and the importance of non-stale data is of a trader making a trade on an out of date price. Another example is given where a person places a bet using odds that are on screen but do not match up with the odds in the betting system.

I just read a post on Comet Daily about a company called Frozen Mountain who have just released a component that adds Comet Support for IIS. Along with this they’ve released a video which doesn’t cover the standard example.

It’s possible that in this example that a polling solution might actually be just as suitable but this is a good demonstration of the benefits of Comet. In the example Comet provides almost instant feedback on the number of available tickets to potential buyers. This has two benefits. The first is that the user (Bob in the video) has less of a chance of missing out on his tickets. The second is more of a commercial benefit in that the user gets instant feedback on the popularity of the event and availability of the tickets and is more likely to make an instant purchase.

Until a solution such as Comet is used the data that a user sees, in a event booking, trading, betting or even search system, cannot be classed as part of the truly real-time web.

Caplin Systems Blog Post – What is the real-time web?

Phil Leggetter — Tue, 28 Apr 2009 15:27:40 +0000

About a week ago I wrote a blog article at work entitled “What is the real-time web?“. I’m seeing even more tweets and posts about the real-time web and I’d love to hear if other people agree with my opinion on what the real-time web is.

View the What is the real-time web? article here.