Abstract
Cloud computing has been widely adopted over the years by practitioners and companies with a variety of requirements. With a strong economic appeal, cloud computing makes possible the idea of computing as a utility, in which computing resources can be consumed and paid for with the same convenience as electricity. One of the main characteristics of cloud as a service is elasticity supported by auto-scaling capabilities. The auto-scaling cloud mechanism allows adjusting resources to meet multiple demands dynamically. The elasticity service is best represented in critical web trading and transaction systems that must satisfy a certain service level agreement (SLA), such as maximum response time limits for different types of inbound requests. Nevertheless, existing cloud infrastructures maintained by different cloud enterprises often offer different cloud service costs for equivalent SLAs upon several factors. The factors might be contract types, VM types, auto-scaling configuration parameters, and incoming workload demand. Identifying a combination of parameters that results in SLA compliance directly in the system is often sophisticated, while the manual analysis is prone to errors due to the huge number of possibilities. This paper proposes the modeling of auto-scaling mechanisms in a typical cloud infrastructure using a stochastic Petri net (SPN) and the employment of a well-established adaptive search metaheuristic (GRASP) to discover critical trade-offs between performance and cost in cloud services.The proposed SPN models enable cloud designers to estimate the metrics of cloud services in accordance with each required SLA such as the best configuration, cost, system response time, and throughput.The auto-scaling SPN model was extensively validated with 95% confidence against a real test-bed scenario with 18.000 samples. A case-study of cloud services was used to investigate the viability of this method and to evaluate the adoptability of the proposed auto-scaling model in practice. On the other hand, the proposed optimization algorithm enables the identification of economic system configuration and parameterization to satisfy required SLA and budget constraints. The adoption of the metaheuristic GRASP approach and the modeling of auto-scaling mechanisms in this work can help search for the optimized-quality solution and operational management for cloud services in practice.
Highlights
Cloud computing is a service-driven computing model whereby an end-user will provide computing resources from a cloud service provider (CSP) in line with an agreedupon service-level agreement (SLA)
Our application of the construction phase in the model can be seen in Algorithm 2. It receives as input the stochastic model, the parameters with possible internal values, α that will determine the size of the candidate restricted list (RCL), β which will be used to increase the variability of solutions [55], the expected workload for the system, and the service level agreement (SLA) of mean response time and throughput
This paper proposes an stochastic Petri net (SPN) model capable of forecasting the behavior of auto-scaling mechanisms in a cloud computing environment
Summary
Cloud computing is a service-driven computing model whereby an end-user will provide computing resources from a cloud service provider (CSP) in line with an agreedupon service-level agreement (SLA). The creation of models is important for predicting the system performance and cost, considering a given workload demand and auto-scaling settings Such models may guide the decision-making for the configuration of cloud infrastructure resources and related elasticity mechanisms. One of the limitations is that the distribution associated with timed transitions must be exponential, which can be bypassed through moment matching techniques, creating new transitions and places This solution can contribute to the other restriction, which is the explosion of the CTMC state space generated by the SPN, making the time for computing the metrics prohibitive [21].
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