A coordination protocol could be carried out in order to coordinate the actions of web services. Outline an architecture for (i) a centralized and (ii) a distributed coordination protocol. In each case, describe the interactions needed to establish coordination between a pair of web services.
What will be an ideal response?
Centralised coordination. A particular server would play the role of coordinator and the web services that require coordination would send their coordination messages to the coordinator, rather like the protocol used in the 2PC. Call the web services A and B, and the coordinator C.
A asks C to create a new context for coordination, which is returned;
A sends B a message, passing on an identifier for the coordination and B communicates with C about it.
In distributed coordination, each participating web service would have a local coordinator that it communicates with and the set of local coordinators would communicate amongst them selves. Call the web services A and B, and their local coordinators Ca and Cb.
A asks Ca to create a new context for coordination, which is returned;
A sends B a message, passing on an identifier for the coordination and B asks Cb to create a context for it.
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