Constantinos Kotsokalis

Establishing and Monitoring SLAs in Complex Service Based Systems

In modern service economies, service provisioning needs to be regulated by complex SLA hierarchies among providers of heterogeneous services, defined at the business, software, and infrastructure layers. Starting from the SLA Management framework defined in the SLA@SOI EU FP7 Integrated Project, we focus on the relationship between establishment and monitoring of such SLAs, showing how the two processes become tightly interleaved in order to provide meaningful mechanisms for SLA management. We first describe the process for SLA establishment adopted within the framework; then,we propose an architecture for monitoring SLAs, which satisfies the two main requirements introduced by SLA establishment: the availability of historical data for evaluating SLA offers and the assessment of the capability to monitor the terms in a SLA offer.

A framework for multi-level SLA management

Service-Oriented Architectures (SOA) represent an architectural shift for building business applications based on loosely-coupled services. In a multi-layered SOA environment the exact conditions under which services are to be delivered can be formally specified by Service Level Agreements (SLAs). However, typical SLAs are just specified at the customer-level and do not allow service providers to manage their IT stack accordingly as they have no insight on how customer-level SLAs translate to metrics or parameters at the various layers of the IT stack. In this paper we present a technical architecture for a multi-level SLA management framework.We discuss the fundamental components and interfaces in this architecture and explain the developed integrated framework. Furthermore, we show results from a qualitative evaluation of the framework in the context of an open reference case.

Fault-tolerant Service Level Agreement lifecycle management in clouds using actor system

Automated Service Level Agreements (SLAs) have been proposed for cloud services as contracts used to record the rights and obligations of service providers and their customers. Automation refers to the electronic formalized representation of SLAs and the management of their lifecycle by autonomous agents. Most recently, SLA automated management is becoming increasingly of importance. In previous work, we have elaborated a utility architecture that optimizes resource deployment according to business policies, as well as a mechanism for optimization in SLA negotiation. We take all that a step further with the application of actor systems as an appropriate theoretical model for fine-grained, yet simplified and practical, monitoring of massive sets of SLAs. We show that this is a realistic approach for the automated management of the complete SLA lifecycle, including negotiation and provisioning, but focus on monitoring as the driver of contemporary scalability requirements. Our proposed work separates the agreements fault-tolerance concerns and strategies into multiple autonomous layers that can be hierarchically combined into an intuitive, parallelized, effective and efficient management structure. We elaborate a utility architecture that optimizes resource deployment.We provide a mechanism for optimized SLA negotiation.Using Actor system as basis, the entire SLA management can be efficiently parallelized.We separate the agreements fault-tolerance strategies into multiple autonomous layers.A realistic approach for the automated management of the complete SLA lifecycle.

Optimal Negotiation of Service Level Agreements for Cloud-Based Services through Autonomous Agents

Cloud-based services have become a cornerstone of todays IT. The self-service feature inherent in Cloud systems allows customers to play a greater role in service procurement. However, this restricts the value propositions and Service Level Agreements (SLAs) that Cloud providers offer because Quality of Service (QoS) and Non Functional Property (NFP) requirements vary from customer to customer. In feature-rich SLA templates, the contract space gets large, objectives are confidential and preferences over QoS and NFP often conflict between providers and customers. Hence, an SLA-gap exists between the two and contemporary providers bind their offerings to the inflexible take-it-or-leave-it SLAs. In this work, we address this problem by presenting a robust and computationally inexpensive negotiation strategy, using which agents can efficiently create near-optimal SLAs under time constraints. Experimental evaluations validate that our strategy performs at par with state of the art learning and non-learning strategies against a variety of metrics including utility, social welfare, social utility and the Pareto-optimal bids. This enables a dynamic SLA negotiation mechanism on top of our OpenShift (PaaS) based Cloud system designed using Service Oriented Cloud Computing Infrastructure (SOCCI) architecture. Negotiated procurement of services is shown to improve satisfaction of participants and reducing the SLA-gap.

SAMI: The SLA Management Instance

The vision for economies of reusable services that can be composed into business processes is still hindered by the lack of dependability as regards their execution. Service Level Agreements (SLAs) are an instrument to express and codify requirements for services, so that an acceptable level of determinism can be provided, and customers can rely on them as such. In this work we present the SLA Management Instance (SAMI) architecture for a reusable autonomic entity that can support negotiation and runtime management of SLAs, without disruptive effects on the existing corresponding services. This architecture takes extra steps towards supporting hierarchies of cross-domain SLAs, reflecting similar hierarchies of cross-domain service compositions.

Modeling Service Level Agreements with Binary Decision Diagrams

The vision of automated service composition for enabling service economies is challenged by many theoretical and technical limitations of current technologies. There is a need for complete, dependable service hierarchies created on-the-fly for critical business environments. Such automatically-constructed, complex and dynamic service hierarchies imply a similarly automated process for establishing the contracts that specify the rules governing the consumption of services; and for binding them into respective contract hierarchies. Deducing these required contracts is a computationally challenging task. This also applies to the optimization of such contract sets to maximize utility. We propose the application of (Shared) Reduced Ordered Binary Decision Diagrams, a suitable graph-based data structure well-known in the area of Electronic Design Automation. These diagrams can be used as a canonical representation of SLAs, thus allowing their efficient and unambiguous management independent of their structures specifics. As such, this representation can facilitate the process of negotiating SLAs, subcontracting parts of them, optimizing their utility, and managing them during runtime for monitoring and enforcement.

QoS-aware SLA-based Advanced Reservation of Infrastructure as a Service

Cloud computing effectively implements the vision of utility computing by employing a pay-as-you-go cost model and allowing on-demand (re-)leasing of IT resources. Small or medium-sized Infrastructure-as-a-Service providers, however, find it challenging to satisfy all requests immediately due to their limited resource capacity. In that situation, both providers and customers may benefit greatly from advanced reservation of virtual resources, i.e. virtual machines. In our work, we assume SLA-based resource requests and introduce an advanced reservation methodology during SLA negotiation by using computational geometry. Thereby, we are able to verify, record and manage the infrastructure resources efficiently. Based on that model, service providers can easily verify the available capacity for satisfying the customers Quality-of-Service requirements. Furthermore, we introduce flexible alternative counter-offers, when the service provider lacks resources. Therefore, our mechanism increases the utilization of the resources and attempts to satisfy as many customers as possible.

Translation of service level agreements: a generic problem definition

A Service Level Agreement (SLA) is the electronic equivalent of a real-life contract, which describes expectations from a service and governs its consumption. Ideally, a SLA provides certainty as regards customer experience and Quality of Service (QoS) received. For self-contained, isolated services this type of certainty is relatively straightforward to achieve. However, for services that are composed by others, or that rely on others to execute, such functional dependencies imply similar non-functional ones. Therefore, SLAs offered by a service to its customers are in turn depending on other SLAs, which the same service establishes in its role as a customer of the services it relies upon. In this paper we explore this dependency between different SLAs, and formalize the problem of converting an agreement for a composed service into individual agreements for the services from which it is composed.

SLA-Based Planning for Multi-Domain Infrastructure as a Service

This paper discusses the problem of planning resource outsourcing and local configurations for infrastructure services that are subject to Service Level Agreements (SLA). The objective of our approach is to minimize implementation and outsourcing costs for reasons of competitiveness, while respecting business policies for profit and risk. We implement a greedy algorithm for outsourcing, using cost and subcontractor reputation as selection criteria; and local resource configurations as a constraint satisfaction problem for acceptable profit and failure risks. Thus, it becomes possible to provide educated price quotes to customers and establish safe electronic contracts automatically. Discarding either local resource provisioning, or outsourcing, models efficiently the specialized cases of infrastructure resellers and isolated infrastructure providers respectively.

Structural optimization of reduced ordered binary decision diagrams for SLA negotiation in iaas of cloud computing

In cloud computing, an automated SLA is an electronic contract used to record the rights and obligations of service providers and customers for their services. SLA negotiation can be a time-consuming process, mainly due to the unpredictable rounds of negotiation and the complicated possible dependencies among SLAs. The operation of negotiating SLAs can be facilitated when SLAs are translated into Reduced Ordered Binary Decision Diagrams (ROBDDs). Nevertheless, an ROBDD may not be optimally structured upon production. In this paper, we show how to reduce the number of 1-paths and nodes of ROBDDs that model SLAs, using ROBDD optimization algorithms. In addition, we demonstrate the reduction of 1-paths via the application of Term Rewriting Systems with mutually exclusive features. Using the latter, ROBDDs can be generated accurately without redundant 1-paths. We apply the principles onto the negotiation of IaaS SLAs via simulation, and show that negotiation is accelerated by assessing fewer SLA proposals (1-paths), while memory consumption is also reduced.