REST – The Good, The Bad and The Ugly
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I recently got a request from Alik for my opinion on REST. I think this might be interesting for a wider audience and decided to blog my answer here.
Note: I also have a REST presentation I prepared a while ago, which is downloadable from here (ppt)
As you probably know REST is an architectural style defined by Roy Fielding for the web which is built on several foundations (client/server, uniform interface etc.) which gives it a lot of strength in affected areas. The top three in my opinion are:
- (relatively) Easy to integrate – a good RESTful API is discoverable from the initial URI onward. This doesn’t suggest that a any application calling on on your service will automagically know what to do. It does mean however that the developer reading your API trying to integrate it has an easier life. Esp. if since hypermedia provides you the roadmap of what to do next.
- Another feature for ease of integration which has to do with REST over HTTP (THE most common implementation of REST ) is the use of ubiquitous standards. Speaking HTTP which is the protocol of the web, emitting JSON or ATOMPub means it is much easier to find a library that can connect to you on any language and platform.
- Scalability – stateless communication, replicated repository make for a good scalability potential.
do note that, as with any architecture/technology – a bad implementation can negate all the benefits other REST goodness are things like the notion of the URI, idempotance of GET in REST over HTTP etc.
Some of the problems of REST aren’t inherent problems of the architectural style but rather drawbacks of the REST over HTTP implementation. Most notable of these is what’s known as “lo-rest” (using just GET and POST) – While technically it might still be RESTful, to me a uniform interface with 2 verbs is too small to be really helpful (which indeed makes a lot of the implementation unRESTful see “The Ugly” below)
One problem which isn’t not HTTP specific is handling REST- programming languages are not resource oriented so the handling code that maps URIs to tends to get messy. Actually Microsoft did a relatively good work with implementing Joe Gregorio’s idea of URI mapping which helps alleviate some of the problem. On the other hand it is relatively hard to make the REST API hyper-text driven (Which is a constraints of REST)
Lastly and most importantly REST is not the answer to everything (see also another post I made on using REST along with other architectural styles) – e.g. most REST implementations I know do not support the notion of pub/sub (Roy did suggest a REST implementation called WAKA that enables this but most people never even heard of it). be weary of the “Hammer” syndrome, REST is a good tool for your toolset but it isn’t the only one.
In my opinion there are 2 main ugly sides for REST. The first is Zealots. That isn’t something unique to REST any good technology/idea (Agile, TDD etc. ) gets its share of followers who think that <insert favorite idea> is the best thing since sliced bread and that everybody should do as they do or else.
The real ugliness comes from the misusers – There’s a lot of mis-understanding. The fact that REST over HTTP has become synonymous with REST leads people to think that HTTP is REST. I recently read a REST book review on Colin’s blog where “the author states that although hypermedia is important in REST it isn't covered in the book because WCF has poor support for it” i.e. a book on REST which ignores one of the important constraints of the style..
Other mis-uses include building an implementation that is GETsful (ie. does everything with http GET) or doing plain RPC where the URI is the command, doing CRUD with HTTP verbs etc. etc.
The point is that REST seems simple but it isn’t – it requires a shift in thinking (e.g. identifying resources, externalizing the state transitions etc.). However, as noted above, done right it can be an important and useful tool in your toolset