Order post-processing

Hi, I have a requirement for post processing on an order.  When the order is complete and paid for, we need to send details to one of several suppliers (based on delivery address) who will fulfill the order shipment (we send them confirmation codes for the payment and they will handle the picking, packaging and delivery).  This is handled using a webservice, so we'd need to make a call to this service once the order process has ended.

What would be the best way of achieving this, and where would we need to add this into the code?  Would it be best done using a plugin?

Thanks.

Create a plugin that handles Order Update Events


    public class MyPlugin : BasePlugin, IConsumer<EntityUpdated<Order>>

We're using v2.1 and I can't find IConsumer in the source.  We're not really in a position to upgrade to 2.3 - is there a way to get around this, or does 2.1 use a different event model?