Cloud users require a set of specific computing needs for their applications, while cloud providers offer a variety of computing products and services on the Internet. These two cloud players make deals through the use of service level agreements (SLAs) where, for instance, prices and levels of quality of service (QoS) are defined. From the cloud user’s point of view, building a robust set of SLAs becomes a challenging problem when multiple cloud providers are present in the market. The allocation of resources in the cloud to run complex applications with guaranteed reliable, secure and acceptable response times is not an easy task, and this paper aims to tackle this problem. This work describes a resource allocation service that aims to optimize the user’s request of cloud resources (virtual machines — VMs) onto multiple Infrastructure-as-a-Service (IaaS) cloud providers. The Resource-Allocation-as-a-Service (RAaaS) proposed in this paper works as a standalone service between cloud users and cloud providers, and it relies on three different requirements: reliability, processing, and mutual trust. The proposed resource allocation service is carried out using the three very common types of VM billing models: on-demand, reserved and spot, where the spot cost model is employed to furnish low-cost resources for the application allocation to improve its reliability. The contributions of this paper are threefold: (i) a three-dimension SLA encompassing reliability, processing, and trust; (ii) an integer linear program (ILP) to schedule cloud-based VMs to applications considering the three-dimension SLA model, and (iii) a heuristic algorithm to mitigate possible QoS violations. Experimental results show that the proposed RAaaS procedure is capable of optimizing resource allocation considering multiple criteria in the SLA while mitigating the extra costs introduced by mutual trust between customers using redundant spot instances allocation.

云用户需要为其应用程序提供一组特定的计算需求，而云提供商则在互联网上提供各种计算产品和服务。这两个云提供商通过使用服务级别协议 (SLA) 进行交易，其中定义了价格和服务质量 (QoS) 级别等。从云用户的角度来看，当市场上存在多个云提供商时，构建一组强大的 SLA 就成为一个具有挑战性的问题。在云中分配资源来运行复杂的应用程序并保证可靠、安全和可接受的响应时间并不是一件容易的事，本文旨在解决这个问题。这项工作描述了一种资源分配服务，旨在优化用户对多个基础设施即服务 (IaaS) 云提供商的云资源（虚拟机 — VM）请求。本文提出的资源分配即服务（RAaaS）作为云用户和云提供商之间的独立服务，它依赖于三个不同的要求：可靠性、处理性和相互信任。所提出的资源分配服务是使用三种非常常见的VM计费模型​​类型来执行的：按需、预留和现货，其中现货成本模型用于为应用程序分配提供低成本资源，以提高其可靠性。本文的贡献有三个方面：(i) 包含可靠性、处理和信任的三维 SLA；(ii) 整数线性程序 (ILP)，用于将基于云的虚拟机调度到考虑三维 SLA 模型的应用程序，以及 (iii) 启发式算法，以减轻可能的 QoS 违规。实验结果表明，所提出的 RAaaS 程序能够考虑 SLA 中的多个标准来优化资源分配，同时减少使用冗余现货实例分配的客户之间的相互信任带来的额外成本。