In a Cloud environment, users face the challenge of selecting and composing resources and services from a single or multiple providers. As several negotiations can occur concurrently, information on service and resource availability may be out-of-date, thus requiring several iterations between users and providers until an agreement is achieved. To address this problem, we introduce CANPRO, a Conflict-Aware Negotiation Protocol for allocating Cloud resource and services aimed at reducing cancellation messages during negotiation. CANPRO allows users (or entities on their behalf) to know the amount of resources being concurrently negotiated by other users and the number of users interested in such an amount, while still keeping users' information private. By knowing this information, users can, for instance, confirm allocation requests with lower chances of having collisions with other users. In addition, for the same reason, users can increase their time deciding which (combination of) resources they want to allocate. The paper presents comparative results of CANPRO against the popular two-phase commit protocol (2PC) and a state-of-the-art protocol named SNAP-3PC. We used think time, network overhead, number of concurrent negotiations and providers as main metrics. The results are promising and the protocol can be used in scenarios other than Cloud Computing; for instance, bookings of health services, cars, tickets for venues, schedule of appointments, among others.
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