Multi-tenant Quality Attributes to Manage Tenants in SaaS Applications

Abstract: Enormous amounts of unstructured data such as images, videos, emails, sensors’ data and documents of multiple types are being generated daily by varied applications. Apart from the challenges related to collection or processing of this data, its efficient storage is also a significant challenge since this data do not conform to any predefined storage model. Therefore, any enterprise dealing with huge unstructured data requires a scalable storage system that can provide data durability and availability at a low cost. The paper proposes a tenant-centric approach to develop an object-based software defined storage system for SaaS multi-tenant applications. We present TOSDS (Tenant-centric Object-based Software Defined Storage), a system that can efficiently meet the storage requirements of users or tenants with diverse needs who are using a multitenant SaaS application. The experimental verification of TOSDS illustrates its effectiveness in storage utilization as well as tenant isolation.

Abstract: Multi-tenancy enables cost-effective SaaS through resource consolidation. Multiple customers, or tenants, are served by a single application instance, and isolation is enforced at the application level. Service load for different tenants can vary over time, requiring applications to scale in and out. A large class of SaaS providers operates legacy applications structured around a relational (SQL) database. These applications achieve tenant isolation through dedicated fields in their relational schema and are not designed to support scaling operations. We present a novel solution for scaling in or out such applications through the migration of a tenant’s data to new application and database instances. Our solution requires no change to the application and incurs no service downtime for non-migrated tenants. It leverages external tables and foreign data wrappers, as supported by major relational databases. We evaluate the approach using two multi-tenant applications: Iomad, an extension of the Moodle Learning Management System, and Camunda, a business process management platform. Our results show the usability of the method, minimally impacting performance for other tenants during migration and leading to increased service capacity after migration.

Abstract: From the Book: Our goals for the first edition were threefold. First, we wanted to show through authentic case studies actual examples of software architectures solving real-world problems. Second, we wanted to establish and show the strong connection between an architecture and an organization's business goals. And third, we wanted to explain the importance of software architecture in achieving the quality goals for a system. Our goals for this second edition are the same, but the passage of time since the writing of the first edition has brought new developments in the field and new understanding of the important underpinnings of software architecture. We reflect the new developments with new case studies and the new understanding both through new chapters and through additions to and elaboration of the existing chapters. Architecture analysis, design, reconstruction, and documentation have all had major developments since the first edition. Architecture analysis has developed into a mature field with industrial-strength methods. This is reflected by a new chapter about the architecture tradeoff analysis method (ATAM). The ATAM has been adopted by industrial organizations as a technique for evaluating their software architectures. Architecture design has also had major developments since the first edition. The capturing of quality requirements, the achievement of those requirements through small-scale and large-scale architectural approaches (tactics and patterns, respectively), and a design method that reflects knowledge of how to achieve qualities are all captured in various chapters. Three new chapters treat understanding quality requirements, achieving qualities, and theattribute driven design (ADD) method, respectively. Architecture reconstruction or reverse engineering is an essential activity for capturing undocumented architectures. It can be used as a portion of a design project, an analysis project, or to provide input into a decision process to determine what to use as a basis for reconstructing an existing system. In the first edition, we briefly mentioned a tool set (Dali) and its uses in the re-engineering context; in in this edition the topic merits its own chapter. Documenting software architectures is another topic that has matured considerably in the recent past. When the first edition was published, the Unified Modeling Language (UML) was just arriving on the scene. Now it is firmly entrenched, a reality reflected by all-new diagrams. But more important, an understanding of what kind of information to capture about an architecture, beyond what notation to use, has emerged. A new chapter covers architecture documentation. The understanding of the application of software architecture to enable organizations to efficiently produce a variety of systems based on a single architecture is summarized in a totally rewritten chapter on software product lines. The chapter reinforces the link between architecture and an organization's business goals, as product lines, based around a software architecture, can enable order-of-magnitude improvements in cost, quality, and time to market. In addition to the architectural developments, the technology for constructing distributed and Web-based systems has become prominent in today's economy. We reflect this trend by updating the World Wide Web chapter, by using Web-based examples for the ATAM chapter and the chapter on building systems from components, by replacing the CORBA case study with one on Enterprise JavaBeans (EJB), and by introducing a case study on a wireless EJB system designed to support wearable computers for maintenance technicians. Finally, we have added a chapter that looks more closely at the financial aspects of architectures. There we introduce a method--the CBAM--for basing architectural decisions on economic criteria, in addition to the technical criteria that we had focused on previously. As in the first edition, we use the architecture business cycle as a unifying motif and all of the case studies are described in terms of the quality goals that motivated the system design and how the architecture for the system achieves those quality goals. In this edition, as in the first, we were very aware that our primary audience is practitioners, so we focus on presenting material that has been found useful in many industrial applications, as well as what we expect practice to be in the near future. We hope that you enjoy reading it at least as much as we enjoyed writing it. 0321154959P12162002

Abstract: Continually verify self-adaptation decisions taken by critical software in response to changes in the operating environment.

Abstract: Multi-tenancy is a relatively new software architecture principle in the realm of the Software as a Service (SaaS) business model. It allows to make full use of the economy of scale, as multiple customers - "tenants" - share the same application and database instance. All the while, the tenants enjoy a highly configurable application, making it appear that the application is deployed on a dedicated server. The major benefits of multi-tenancy are increased utilization of hardware resources and improved ease of maintenance, in particular on the deployment side. These benefits should result in lower overall application costs, making the technology attractive for service providers targeting small and medium enterprises (SME). However, as this paper advocates, a wrong architectural choice might entail that multi-tenancy becomes a maintenance nightmare.

Abstract: Cloud computing is a style of computing in which dynamically scalable and often virtualized resources are provided as a service over the Internet. One type of cloud service, SaaS is commonly utilized and it provides several benefits to service consumers. To realize these benefits, it is essential to evaluate the quality of SaaS and manage relatively higher level of its quality based on the evaluation result. Hence, there is a high demand for devising a quality model to evaluate SaaS cloud services. Conventional frameworks do not effectively support SaaS-specific quality aspects such as reusability and accessibility. In this paper, we propose a comprehensive model for evaluating quality of SaaS. We first define key features of SaaS. And then, we derive quality attributes from the key features, and define metrics for the quality attributes. To validate our quality model for SaaS, we conduct assessment based on IEEE 1061. By using the proposed SaaS quality model, SaaS can be evaluated by both service providers. Furthermore, the evaluation results are utilized as an indicator for SaaS quality management.

Abstract: Increasingly, systems must have the ability to self-adapt to meet changes in their execution environment. Unfortunately, existing solutions require human oversight, or are limited in the kinds of systems and the set of quality-of-service concerns they address. Our approach, embodied in a system called Rainbow, uses software architecture models and architectural styles to overcome existing limitations. It provides an engineering approach and a framework of mechanisms to monitor a target system and its environment, reflect observations into a system’s architecture model, detect opportunities for improvement, select a course of action, and effect changes in a closed loop. The framework provides general and reusable infrastructures with well-defined customization points, allowing engineers to systematically customize Rainbow to particular systems and concerns.