Evolving Multi-tenant SaaS Applications through Self-Adaptive Upgrade Enactment and Tenant Mediation

When successful, multi-tenant SaaS applications service many customer organizations (tenants) at once, and SaaS providers face the challenge of complying to the different SLAs of each of these tenants. As a consequence, evolving a SaaS application is in practice done at run time to limit service disruptions, and preferably on a gradual, tenant-per-tenant basis, while taking into account the nature of the upgrade at hand but also these different tenant SLAs. The economic viability and cost-effectiveness of a SaaS offering depends strongly on two principles: (i) maximal automation of its operation, and (ii) self-service: allowing tenant organizations themselves to customize and configure different aspects of the service to their specific needs. In this position paper, we highlight the value of adopting the principles of self-adaptive systems in the design of middleware solutions that support continuous evolution of multi-tenant SaaS applications as a means to implement the first principle. Furthermore, we discuss the additional challenges imposed by the second principle, more specifically for supporting tenant mediation, i.e. introducing human stakeholders such as tenant administrators into the inner control-loop of a self-adaptive system. We present the design of our middleware that addresses these challenges for the specific purpose of evolving multi-tenant SaaS applications, but also discuss the relevance for self-adaptive systems that support stakeholder mediation in general.