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In the last months I have studied and worked a lot with web services in general, and more specifically the RESTful ones. I believe we are going through a fast maturation process in this area, and RESTful web services are becoming the preferred choice for many new implementations. Right in the thick of things in this field is the Atom Publishing Protocol. This is the blueprint solution for RESTful web services, and its adoption is growing fast, reaching much broader scope than just blog applications using the Atom Format.The Atom format and AtomPub protocol can both be used for many interesting purposes. This year I’m working on a big refactoring (actually a new implementation) of a widely used Globo.com application. This application (let’s call it Register) is responsible for the creation of new users and provisioning new services to them, among other features.
A nice concept present in the original development is the use of Application Connectors. Through these connectors, other applications get notified of events that happened in the Register application. An example is: when a new subscriber (a paying user) is created, a connector sends the notification to another application in order to create the subscriber’s mailbox in the company’s external mail provider. Another example is: when a user gets provisioned in the blogging service, another connector sends a notification to the blogger application, that does what it needs in order to create the user’s directory and quota on the file server.
Although i like this concept, it currently has some problems. This connector’s invocation is done explicitly by the Register application. The Register application knows that a new subscriber must receive a new mailbox, and it needs to call a given connector to do this. This is my biggest concern with the current implementation. I strongly believe that an application that creates users must not know anything about mailboxes. In the current structure, when a new application ABC must be notified of events in application XYZ, application XYZ must be modified to invoke a new connector. This doesn’t please me at all. Let me explain a solution that pleases me more 😉
To explain my idea, I’ll propose some examples involving Google and its services. As we all know, Google offers several different services, all of which can be accessed using the same Google account. When you register at Google, you receive a mail account. Let’s suppose that Google Register application sends a new entry to an Atom feed every time a new user is created. This way, every user creation is present on the Atom Feed. If an application (for example Google Mail) needs to be notified of the creation of new users, it just needs to subscribe to the Register’s Atom feed.
Let me propose a richer example now. Let’s say Google starts to offer some super cool software development services. If you’re a developer, you can ask them to give you a “development account”. This development account would give you access to a Subversion repository, a Bugzilla project and a MySql database. Each of these would be an independent service offered by them, subject to change at any given time. The activation of “development accounts” could also populate an Atom feed.
This way the Subversion, Bugzilla and MySql services could be subscribers of the feed, doing everything they need when a new development account is activated, in asynchronous manner. The application that activates the development account has no knowledge of any other services. If Google wants to offer new services such as a Maven repository or a Continuous Integration environment, no problem. The new services would just subscribe to the Atom feed and do whatever they need when a new account is activated.
If Google wants to offer a free development account and a non-free account with better features, there could be another Atom feed for the activation of the paying accounts or maybe updates to the same existing feed. The Register application would know only about registrations, and other components could be easily plugged and unplugged from this process, without modifications on the Register application. Ah, and worth mentioning… totally decoupled from any specific platform. I don’t know how to implement any kind of messaging more decoupled than that.
This is much much better than the way our Register application sends notifications currently. And I’ll be pretty happy once we manage to do this, it’ll be so cool!
By the way, these Google’s software development services would be awesome. My friend Bairos kindly provides me Subversion and Trac services, but he doesn’t have Google’s bandwidth 🙂 Let’s hope Google gets to know about this and starts offering these services. It’d be amazing!