Vasilios Andrikopoulos

How to adapt applications for the Cloud environment Challenges and solutions in migrating applications to the Cloud

The migration of existing applications to the Cloud requires adapting them to a new computing paradigm. Existing works have focused on migrating the whole application stack by means of virtualization and deployment on the Cloud, delegating the required adaptation effort to the level of resource management. With the proliferation of Cloud services allowing for more flexibility and better control over the application migration, the migration of individual application layers, or even individual architectural components to the Cloud, becomes possible. Towards this goal, in this work we focus on the challenges and solutions for each layer when migrating different parts of the application to the Cloud. We categorize different migration types and identify the potential impact and adaptation needs for each of these types on the application layers based on an exhaustive survey of the State of the Art. We also investigate various cross-cutting concerns that need to be considered for the migration of the application, and position them with respect to the identified migration types. Finally, we present some of the open research issues in the field and position our future work targeting these research questions.

On the Evolution of Services

In an environment of constant change and variation driven by competition and innovation, a software service can rarely remain stable. Being able to manage and control the evolution of services is therefore an important goal for the Service-Oriented paradigm. This work extends existing and widely adopted theories from software engineering, programming languages, service-oriented computing, and other related fields to provide the fundamental ingredients required to guarantee that spurious results and inconsistencies that may occur due to uncontrolled service changes are avoided. The paper provides a unifying theoretical framework for controlling the evolution of services that deals with structural, behavioral, and QoS level-induced service changes in a type-safe manner, ensuring correct versioning transitions so that previous clients can use a versioned service in a consistent manner.

Supporting the Migration of Applications to the Cloud through a Decision Support System

The motivation for this work is the necessity to be able to select an appropriate Cloud service provider offering for the migration of existing applications, based on cost minimization. While service providers offer pricing information publicly, and online tools allow for the calculation of cost for various Cloud offerings, the selection of which offering fits better the application requirements is left to application developers. For this purpose, this work proposes a migration decision support system that incorporates both offering matching and cost calculation, combining features from various approaches in the State of the Art. The proposed approach is then evaluated against existing tools.

Evolving Services from a Contractual Perspective

In an environment of constant change, driven by competition and innovation, a service can rarely remain stable - especially when it depends on other services to fulfill its functionality. However, uncontrolled changes can easily break the existing relationships between a service and its environment (its customers and providers). In this paper we present an approach that allows for the controlled evolution of a service by leveraging the loosely-coupled nature of the SOA paradigm. More specifically, we formalize the notion of contracts between interacting services that enable their independent evolution and we investigate under which criteria can changes to a contract-bound service, or even to the contract itself, be transparent to the environment of the service.

Optimal Distribution of Applications in the Cloud

The emergence of the cloud computing paradigm introduces a number of challenges and opportunities to application and system developers. The multiplication and proliferation of available offerings by cloud service providers, for example, makes the selection of an appropriate solution complex and inefficient. On the other hand, this availability of offerings creates additional possibilities in the way that applications can be engineered or re-engineered to take advantage of e.g. the elastic nature, or the pay per use model of cloud computing. This work proposes a formal framework which allows to explore the possibility space of optimally distributing application components across cloud offerings in an efficient and flexible manner. The proposed approach introduces a set of innovative in their use concepts and demonstrates how this framework can be used in practice by means of a running scenario.

ESB MT : Enabling Multi-Tenancy in Enterprise Service Buses

Multi-tenancy is an essential property of Cloud computing. It helps service providers to maximize resource utilization and reduce servicing costs per customer. It is therefore important for key components of the contemporary enterprise environment like the Enterprise Service Bus (ESB) to support and enable multi-tenancy. For this purpose, in this work we investigate the requirements for multi-tenant ESB solutions, propose an implementation-agnostic ESB architecture that addresses these requirements, and discuss our proof-of-concept realization of this architecture.

Automated Capturing and Systematic Usage of DevOps Knowledge for Cloud Applications

DevOps is an emerging paradigm to actively foster the collaboration between system developers and operations in order to enable efficient end-to-end automation of software deployment and management processes. DevOps is typically combined with Cloud computing, which enables rapid, on-demand provisioning of underlying resources such as virtual servers, storage, or database instances using APIs in a self-service manner. Today, an ever-growing amount of DevOps tools, reusable artifacts such as scripts, and Cloud services are available to implement DevOps automation. Thus, informed decision making on the appropriate approach (es) for the needs of an application is hard. In this work we present a collaborative and holistic approach to capture DevOps knowledge in a knowledgebase. Beside the ability to capture expert knowledge and utilize crowd sourcing approaches, we implemented a crawling framework to automatically discover and capture DevOps knowledge. Moreover, we show how this knowledge is utilized to deploy and operate Cloud applications.

Enabling tenant-aware administration and management for JBI environments

Enterprise Service Buses (ESBs) constitute a core middleware technology for each modern Service-Oriented Architecture (SOA) solution. Given the popularity of the Cloud paradigm, which is based on fundamental SOA concepts, it is only therefore natural to look into how ESBs can be transformed into native building blocks for Cloud platforms. As a first step of this effort, in this work we investigate how ESBs can become multi-tenant aware, i.e. able to support multiple tenants and their users sharing the same ESB instance. A generalized architecture based on the JBI specification implemented by a number of open source ESBs is presented for this purpose. We demonstrate the feasibility of our proposal by means of a proof of concept realization and we evaluate the performance of our solution against a non multi-tenant ESB that was used as the baseline for our implementation.

Retrieving Compatible Web Services

Service retrieval holds a central role during the development of Web services and Service-Based Applications (SBAs). The higher the number of available services, the more complex it becomes to locate the service closer to the developer needs. The complexity increases further with the number of available service versions that could also be suitable for this purpose. Existing approaches on service retrieval use a similarity measure between service interfaces to identify potentially relevant services. In this work we focus on introducing information about the compatibility of services while calculating their similarity as the means for providing more suitable results. For this purpose we update and extend an existing Web services matchmaker called UDDI Registry by Example (URBE).

Non-functional data layer patterns for Cloud applications

Cloud services allow for hosting applications partially or completely in the Cloud by migrating their components and data. Especially with respect to data migration, a series of functional and non-functional challenges like data confidentiality arise when considering private and public Cloud data stores. In this paper we identify some of these challenges and propose a set of reusable solutions focusing on the non-functional aspects, organized together as a set of Cloud Data Patterns.