Dynamic SLAs for Clouds
In the Cloud domain, to guarantee adaptation to the needs of users and providers, Service-Level-Agreements (SLAs) would benefit from mechanisms to capture the dynamism of services. The existing SLA languages attempt to address this challenge by focusing o
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IMT School for Advanced Studies Lucca, Lucca, Italy {rafael.uriarte,rocco.denicola}@imtlucca.it 2 University of Camerino, Camerino, Italy [email protected]
Abstract. In the Cloud domain, to guarantee adaptation to the needs of users and providers, Service-Level-Agreements (SLAs) would benefit from mechanisms to capture the dynamism of services. The existing SLA languages attempt to address this challenge by focusing on renegotiation of the agreement terms, which is a heavy-weight process, not really suitable for dealing with cloud dynamism. In this paper, we propose an extension of SLAC, a SLA language for clouds that we have recently defined, with a mechanism that enable dynamic modifications of the service agreement. We formally describe this extension, implement it in the SLAC framework and analyse the impacts of dynamic SLAs in some applications. The advantages of dynamic SLAs are demonstrated by comparing their effect with that of static SLA and of the “renegotiation” approach.
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Introduction
The cloud paradigm is inherently dynamic from both the consumer and the provider perspectives. From the provider’s standpoint, new resources are added and removed on-the-fly, whilst service requests and prices vary over time as the pay-per-use model is employed. From the consumer’s perspective, instead, the requirements may vary considerably when, e.g., clouds are used to outsource internal services or to complement the computing capacity through a hybrid cloud. Such dynamism might change providers and consumers requirements during the service provision period. Providers might need to change the agreements, e.g., to avoid the violation of agreements and to maximise revenues by serving consumers willing to pay for immediate use of the service [6]. On the other hand, consumers may modify the service, e.g., to respond to unexpected demands, to extend the expiration date of a contract or to change the amount of resources to be provided. Clouds commonly use Service-Level-Agreements (SLAs) to regulate the provision of services. A SLA is the formalisation of the service provision characteristics, which are composed of obligations, rights and guarantees for the involved parties. In clouds, where consumers entrust crucial data and processes to other c IFIP International Federation for Information Processing 2016 Published by Springer International Publishing Switzerland 2016. All Rights Reserved M. Aiello et al. (Eds.): ESOCC 2016, LNCS 9846, pp. 34–49, 2016. DOI: 10.1007/978-3-319-44482-6 3
Dynamic SLAs for Clouds
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parties, SLAs are necessary and reflecting cloud’s dynamism in contracts is a crucial open issue. The need for dynamicity can be perceived by considering a situation in which a cloud provider has overbooked its resources and the load unexpectedly raises. In such case, the provider to avoid breaching SLAs, paying fines and violating the consumers’ trust, might want to activate a clause in the contract that allows him to reduce the resources provided to some consumers (e.g., number of VMs) offering monetary
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