Someone at AMEE pointed out to me that there’s been a flurry of activity around so-called “Web Hooks” when I referred to the concept. This is quite heartening as I thought of this a couple of years ago and implemented this in Smartmessages early last year! I call them callbacks, but the idea is the same – it’s essentially a distributed observer pattern. I couldn’t figure out why nobody seemed to understand what I was on about… When I get some interesting event (e.g. a message open, mailshot completion, clickthrough etc), I ping a user-supplied URL with the appropriate event data, pretty much the one-liner that Jeff alludes to. The reason we do it is that sync with external systems (usually CRM) is something that were always running into, and there seems to be no sensible, generic way of dealing with it other than this, so I’m surprised it has not been discussed in this context before.
There’s one downside as far as I can see – it is highly dependent on the receiver to be able to handle the event in a timely fashion. This isn’t an issue if you’re connecting say, Yahoo! to Google, but it could be a big problem if you connect Google to your WordPress blog… My experience of CRM systems is that they are simply too slow to cope with the high rates of traffic that we are likely to generate, for example, if we point a stream of ~200 events per second at a CRM system, it will probably just bog down and fail (I’m thinking of the SalesForce API here which typically takes 1-2 sec to deal with a single SOAP API call). Retrying will only make this worse. I have two solutions for this: limit events to those that don’t happen so often (kind of lame!), or alternatively, use an outbound message queue to rate-limit the sending (Amazon SQS and Memcacheq spring to mind). Queueing works, but you lose some of the real-time aspect. Ideally clients would implement their own incoming queue in order to allow them to process events at their leisure, but this is mostly beyond the vast majority of web authors (or at least those that host the CRM systems that we hear from!).
Anyway, it’s nice to know that I’m not completely barking…
PHP London Conference 2009
From this truly excellent conference, I took away some good memories, some new ideas and a nasty bout of conference flu. There’s nothing quite like being in close proximity to a few hundred people to really spread things around…
Highlight for me was Aral Balkan‘s keynote. It’s always nice to see someone showing plain enthusiasm, and I couldn’t agree more with him about the “lost magic” of computing. Had a chat with him afterwards about AMEE and other things. He also seems to have put together some odd but dull things that I had noticed a need for – EU VAT codings and ISO language references as web services!
I didn’t really enjoy David Soria Parra’s talk on sharding. It all came across as very negative and many of the ways of doing it and coping with the fallout were not really discussed. No mention of MySQL 5.1’s partitioning (which is limited, but is at least a start), or more radical approaches like Sequoia.
David Axmark’s talk on Drizzle was more interesting than I expected, nice to see effort being put into this direction.
Microsoft really does seem to be trying a bit harder these days – their CSS test suite for IE8 is very welcome, and the effort they are putting into PHP, apache and other projects benefits many people. It has to be said that while it’s not a mainstream product, Surface is really pretty cool to play with.
Chris Shiflett’s talk was excellent too; his demos and examples were particularly good, and entertaining.
The post-conference social was great fun, I met lots of nice new people. After our move to France I suspect it will be harder to get to events like this, so I should make the most of them while I can!
I’ve had several ideas for talks that I’d like to do (I get sick of email sometimes!), so I guess I need to get a bit more proactive on actually submitting them to a call for papers.