Basic component of ESB. Other components are build on top of mediators. When a message come to a mediator, it transform that message according to the configuration defined of that mediator and output another the message according to the configuration defined. In mediators some kind of processing will happen.
Sequences (sequence of mediators)
we need several mediators to achieve the requirement so we can have a chain of mediators define as a sequence.
A logical entity to which we are sending the messages from ESB it is actual back end. It can be Http url, JMS end point. There the quality of service parameters can be defined (eg : time out value of end point, retry count).
A virtual service hosted in ESB. A actual entity that client can see. When a client send a message to ESB it will come to one of proxy services (In sequence, out sequence, fault sequence). In sequence is a sequence which receive message from client. After receives, it will execute the mediators defined in that in sequence. After processing the message, it will send to the end point defined in that in sequence. In that, send mediator is used to send message to back end. Then message is routed to the particular service. That server will send a response back to the ESB. Then the response will be retrieve from the out sequence. There response can be send to client or to another service.
If any error occur in back end call then the error will come to the error sequence. Depending on our requirements the fault sequence can be used log the error, ignore it or send a SOAP fault back to the client indicating that something went wrong.
In here also we have In sequence, out sequence, fault sequence.
Consider a web page with SOAP service, client send request in REST, we can use ESB to transform. Inside ESB REST API will be defined. When client send the message to REST API, the ESB will send SOP message to back end. The response will come as SOAP message then it transform into REST and send it to the client.
Connector is used to connect the cloud based APIs(facebook,linkedin,JIRA) with ESB.