Consumer and Provider Roles

Consumer and Provider Roles

When we speak of the Consumer and Provider roles for the ServiceMix components, the difference is very subtle at first sight, but very important from a programmer perspective. The following figure shows the Consumer and Provider roles in the ServiceMix ESB:

The above figure shows two instances of servicemix-http deployed in the ServiceMix ESB, one in a provider role and the other in the consumer role. As it is evident, these roles are with respect to the NMR of the ESB. In other words, a consumer role implies that the component is a consumer to the NMR whereas a provider role implies the NMR is the consumer to the component. Based on these roles, the NMR will take responsibility of any format or protocol conversions for the interacting components.

Let us also introduce two more parties here to make the role of a consumer and a provider clear—a client and a service. In a traditional programming paradigm, the client interacts directly with the server (or service) to avail the functionality. In the ESB model, both the client and the service interact with each other only through the ESB. Hence, the client and the service need peers with their respective roles assigned, which in turn will interact with each other. Thus, the ESB consumer and provider roles can be regarded as the peer roles for the client and the service respectively.

Any client request will be delegated to the consumer peer who in turn interacts with the NMR. This is because the client is unaware of the ESB and the NMR protocol or format. However, the servicemix-http consumer knows how to interact with the NMR. Hence any request from the client will be translated by the servicemix-http consumer and delivered to the NMR.

On the service side also, the NMR needs to invoke the service. But the server service is neutral of any specific vendor's NMR and doesn't understand the NMR language as such. A peer provider role will help here. The provider receives the request from the NMR, translates it into the actual format or protocol of the server service and invokes the service. Any response will also follow the reverse sequence.