Abstract
A challenge, when implementing multi-tenancy in a cloud-hosted software service, is how to ensure that the performance and resource consumption of one tenant does not adversely affect other tenants. Software designers and architects must achieve an optimal degree of tenant isolation for their chosen application requirements. The objective of this research is to reveal the trade-offs, commonalities, and differences to be considered when implementing the required degree of tenant isolation. This research uses a cross-case analysis of selected open source cloud-hosted software engineering tools to empirically evaluate varying degrees of isolation between tenants. Our research reveals five commonalities across the case studies: disk space reduction, use of locking, low cloud resource consumption, customization and use of plug-in architecture, and choice of multi-tenancy pattern. Two of these common factors compromise tenant isolation. The degree of isolation is reduced when there is no strategy to reduce disk space and customization and plug-in architecture is not adopted. In contrast, the degree of isolation improves when careful consideration is given to how to handle a high workload, locking of data and processes is used to prevent clashes between multiple tenants and selection of appropriate multi-tenancy pattern. The research also revealed five case study differences: size of generated data, cloud resource consumption, sensitivity to workload changes, the effect of the software process, client latency and bandwidth, and type of software process. The degree of isolation is impaired, in our results, by the large size of generated data, high resource consumption by certain software processes, high or fluctuating workload, low client latency, and bandwidth when transferring multiple files between repositories. Additionally, this research provides a novel explanatory framework for (i) mapping tenant isolation to different software development processes, cloud resources and layers of the cloud stack; and (ii) explaining the different trade-offs to consider affecting tenant isolation (i.e. resource sharing, the number of users/requests, customizability, the size of generated data, the scope of control of the cloud application stack and business constraints) when implementing multi-tenant cloud-hosted software services. This research suggests that software architects have to pay attention to the trade-offs, commonalities, and differences we identify to achieve their degree of tenant isolation requirements.
Highlights
Cloud services are applications delivered over the Internet [1] that offer users on-demand access to shared resources such as infrastructures, hardware platforms, and software application functionality [2].Cloud services provide a dedicated instance of applications to multiple users using multitenancy
The large size of generated data, high resource consumption processes, high or fluctuating workload, low client latency, and bandwidth when transferring multiple files between repositories reduces the degree of isolation
Cross-case analysis we present the results of the cross-case analysis that was applied in an iterative manner during the analysis to reach the conclusion
Summary
Cloud services are applications delivered over the Internet [1] that offer users on-demand access to shared resources such as infrastructures, hardware platforms, and software application functionality [2]. Cloud services provide a dedicated instance of applications to multiple users using multitenancy. Multitenancy allows a single instance of a service to serve multiple users while retaining dedicated configuration information, application data and user management for each tenant [3]. Software architects need to be able to control the required degree of isolation between tenants sharing components of a cloud-hosted application [4]. Varying degrees of tenant isolation is possible, depending on the type of component being shared, the process supported by the component and the location of the component on the cloud application stack (i.e., application level, platform level, or infrastructure level) [3]. The degree of isolation required for a component that cannot be shared due to strict laws and regulations would be much higher than that of a component that has to be reconfigured for some tenants with specific requirements
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