Efficient customization of multi-tenant SaaS

Transcription

1 Efficient customization of multi-tenant SaaS Stefan Walraven, Bert Lagaisse, Wouter Joosen 1 Challenges for the customization of SaaS Software as a Service (SaaS) has been increasingly adopted by software vendors as their main software delivery model, as it provides the opportunity to offer their software applications to a larger market and to benefit from the economies of scale. If well-achieved by the SaaS provider, these benefits add value to the offering and reduce the operational costs of hosting and maintaining the SaaS application. As explained in our previous article of this series, one of the key enablers to leverage economies of scale is multi-tenancy: resources are shared among multiple customer organizations (the so-called tenants), which leads to higher resource utilization and scalability. The highest degree of resource sharing is achieved with application-level multi-tenancy [1, 4]: end users from different tenants are simultaneously served by a single application instance on top of shared hardware and software infrastructure. However, this focus on increased resource sharing typically results in a onesize-fits-all approach (see Fig. 1). As a consequence, multi-tenant SaaS applications are inherently limited in terms of flexibility and variability, and cannot be customized to the different and varying requirements of the different tenants. This makes it hard for a SaaS provider to differentiate from competitors [5]: every tenant is unique with its own requirements, and consequently standardized functionalities and services lose their value as these requirements become more complex and diverse [3]. Especially in the case of cloud computing with its potentially large customer base, mass customization becomes increasingly relevant, i.e. offering software services tailored to the tenant s needs, where and when they need it, and at a price similar to the default (non-customizable) alternative [2, 3]. We have identified the following concrete challenges with respect to the customization of multi-tenant SaaS applications [6]: 1. Increased engineering complexity. Application-level multi-tenancy already introduces additional application engineering complexity for the SaaS provider to ensure the necessary isolation between the different tenants as well as to provide a tenant-specific management facility [4] (see Fig. 1). In addition, customizations have to be isolated so that they only apply to a particular tenant and do not affect the service behaviour that is delivered to other tenants (e.g. functionality, performance, security). Support for such concurrent tenant-specific customizations is lacking in the current state of practice in application middleware and PaaS platforms, which This paper was first published on 1

2 Figure 1: Illustration of the trade-off between high cost efficiency and scalability versus high isolation, flexibility and low engineering cost, in the context of the different architectural strategies for multi-tenancy. results in complex software constructions at the application level and high performance overhead. 2. Explosion of variations. Mass customization of the SaaS application tailored to the different and varying requirements of all tenants leads to an explosion of variations. Furthermore, continuous maintenance and evolution of the application (e.g. patches or upgrades) will only enhance this effect with different versions of the application as well as the different variations. This problem worsens with the success of a SaaS offering: with an increasing amount of tenants the degree of variability becomes unmanageable by the SaaS provider, and thus threatens the crucial scalability and cost efficiency [5]. In the remainder of this white paper we discuss an overview our research to achieve efficient customization of multi-tenant SaaS. In the next section, we first present the key research goals and our approach. Section 3 discusses our contributions, and summarizes our key publications in the domain. 2 Goals and approach Customization of SaaS applications involves non-trivial challenges with respect to the software engineering approach as well as the supporting middleware. Consequently, the overall goal of this research is the study, development and evaluation of methods and technologies to develop and run cost-efficient and customizable SaaS applications, while preserving the key benefits of cloud computing such as scalability. More specifically, the focus is on tackling the trade-off presented above (cf. Fig. 1) by introducing flexibility into multi-tenant SaaS applications. We break up this goal into the following subgoals: 2

3 1. Dynamic and context-sensitive adaptation and composition. A multitenant SaaS application should adapt at run time based on the current context. This context is defined by the tenant associated to the current interaction and its specific requirements, as well as by the state and behaviour of the cloud environment (e.g. the current load has an impact on performance). Because a multi-tenant application is shared between end users of multiple tenants, variants for different tenants have to be composed and activated concurrently within the same SaaS application instance. Therefore, it is critical that these co-existing variants are isolated from each other, i.e. the adaptations should occur within the scope of a single tenant and may not have an impact on other tenants. 2. Scalable variability management. Variability emerges from different and varying tenant requirements, maintenance and evolution, and has a high impact on the manageability and thus scalability of the SaaS application. To avoid an explosion of variations, the versatility of software variations should be improved. More specifically, customizations, driven by highlevel configurations, have to be automatically translated into the composition of a set of reusable software modules. Furthermore, a part of the configuration complexity should be shifted towards the tenant (i.e. selfservice) to maintain the scalability with an increasing amount of tenants. To achieve this, we combined the concepts and method of software product line engineering (SPLE) with the flexibility of adaptive middleware. As current cloud-enabling middleware and PaaS offerings do not sufficiently support the development and customization of multi-tenant SaaS applications [9], we developed an advanced middleware framework that builds upon these existing platforms and that provides the necessary support to realize the run-time and context-sensitive composition of tenant-specific variants within the same application instance. It is a framework in the sense that it provides both a versatile architecture that supports different implementations and deployments, and a set of reusable, loosely-coupled components that implement key parts of the architecture. However, the SaaS model as well as leveraging this advanced middleware framework for hosting a customizable SaaS application have an impact on the applied software engineering method. Therefore, there is also a need for engineering support for SaaS architects and developers. Because of the customization needs, we have proposed a method similar to SPLE, called service line engineering (SLE), for the efficient development, operation and management of customizable SaaS applications. 3 Key contributions During our research on efficient customization of multi-tenant SaaS we realized the following contributions to the state of the art in multiple research domains: 1. Runtime composition of software variants in multi-tenant, multi-tier applications; 2. Runtime enforcement of performance isolation between tenants; 3

4 3. The service line engineering method to manage variability in multi-tenant SaaS applications. In the following subsections we briefly summarize these key contributions. For further reading on these contributions and research topics, we refer to the more extensive technical papers for the interested reader. 3.1 Middleware support for co-existing variants in multitenant SaaS applications The advanced middleware framework (i) complements existing cloud-enabling middleware and PaaS offerings, and (ii) improves flexibility of multi-tenant SaaS applications by enabling tenant-specific customizations, while (iii) preserving the operational cost benefits (thus economies of scale) and limiting the engineering complexity. Concretely, tenants can customize the multi-tenant SaaS application to their specific functional and non-functional requirements via a feature-based configuration interface. Based on these tenant-specific configurations and the current context, the middleware layer dynamically performs the end-to-end customization throughout the distributed SaaS application on a per tenant basis. Two specific instances of this middleware framework have been developed with focus on: The run-time composition of software variants in multi-tier componentbased SaaS applications driven by tenant-specific configurations. We have implemented a prototype on top of Google App Engine (GAE), and its evaluation in the context of an online hotel booking application shows improved flexibility with little impact on the operational costs [8]. The run-time enforcement of performance isolation in compliance with tenant-specific SLAs over distributed environments for multi-tenant SaaS. The prototype implementation on a JBoss AS-based private cloud platform has been evaluated using a real-world, workflow-based SaaS offering in the domain of online B2B document processing, introducing only limited performance overhead [7]. 3.2 Service line engineering method The service line engineering (SLE) method facilitates SaaS providers to introduce and manage variability in multi-tenant SaaS applications without compromising the scalability. The concept of a service line is based on the notion of software product lines, but offers a shared application instance that still is dynamically customizable to different tenant-specific requirements. The SLE method is highly integrated and generic, in the sense that the feature-level variability is consistently and explicitly supported in each of the subsequent stages, while these stages are open for existing work to be leveraged upon. The application of this method results (i) in efficiency benefits with respect to addressing the management complexity of many co-existing tenant-specific configurations in a customizable SaaS application, and (ii) in a significant reduction of effort to provision tenants (i.e. configuring and composing an application variant) as well as to update and maintain the service line as a whole, though 4

5 at the expense of a higher initial development effort. The SLE method has also been validated in the development of the B2B document processing SaaS application [11, 10]. 4 Conclusion In this white paper we focused on the challenge of customizing multi-tenant SaaS applications based on the specific requirements of the different co-existing tenants, without compromising the key benefits of cloud computing, such as cost efficiency and scalability. To address this challenge, we have presented our feature-based approach, which is twofold and maps to two core contributions: (i) a middleware framework to support co-existing variants in multi-tenant SaaS applications, and (ii) a software engineering method, called service line engineering (SLE), to introduce and manage variability throughout the entire lifecycle of multi-tenant SaaS applications. References [1] Frederick Chong and Gianpaolo Carraro. Architecture strategies for catching the long tail. aa aspx, Microsoft Corporation. [2] Stanley M. Davis. From future perfect : Mass customizing. Strategy & Leadership, 17(2):16 21, [3] Toby B. Gooley. Mass customization: How logistics makes it happen. Logistics Management & Distribution Report, 37(4):49 52, [4] Chang Jie Guo, Wei Sun, Ying Huang, Zhi Hu Wang, and Bo Gao. A framework for native multi-tenancy application development and management. In CEC/EEE 07: 9th IEEE International Conference on E-Commerce Technology and 4th IEEE International Conference on Enterprise Computing, E-Commerce, and E-Services, pages IEEE, [5] Wei Sun, Xin Zhang, Chang Jie Guo, Pei Sun, and Hui Su. Software as a Service: Configuration and customization perspectives. In SERVICES-2 08: IEEE Congress on Services Part II, pages 18 25, [6] Stefan Walraven. Middleware and methods for customizable SaaS. PhD thesis, Department of Computer Science, KU Leuven, [7] Stefan Walraven, Wouter De Borger, Bart Vanbrabant, Bert Lagaisse, Dimitri Van Landuyt, and Wouter Joosen. Adaptive performance isolation middleware for multi-tenant SaaS. In UCC 15: Proceedings of the 2015 IEEE/ACM 8th International Conference on Utility and Cloud Computing, December [8] Stefan Walraven, Eddy Truyen, and Wouter Joosen. A middleware layer for flexible and cost-efficient multi-tenant applications. In Middleware 11: Proceedings of the 12th ACM/IFIP/USENIX International Conference on Middleware, pages Springer Berlin / Heidelberg,

6 [9] Stefan Walraven, Eddy Truyen, and Wouter Joosen. Comparing PaaS offerings in light of SaaS development. Computing, 96(8): , [10] Stefan Walraven, Dimitri Van Landuyt, Fatih Gey, and Wouter Joosen. Service line engineering in practice: Developing an integrated document processing SaaS application. CW Reports 652 (2nd revised), Department of Computer Science, KU Leuven, be/handle/ / [11] Stefan Walraven, Dimitri Van Landuyt, Eddy Truyen, Koen Handekyn, and Wouter Joosen. Efficient customization of multi-tenant Software-as-a- Service applications with service lines. Journal of Systems and Software, 91:48 62,