Recently when talking to an enterprise customer about SaaS and multi-tenancy considerations and it became clear that our guidance around architecting for SaaS is being read and applied. I think this is partly because reference implementations like Litware help to show the practical application of the guidance to the solution architects and developers.
The interesting aspect of the conversation was that, after the architects have applied the pattern for single-instance multi-tenancy to their individual SaaS applications, the cross-cutting concerns start to emerge around multi-application, multi-tenancy. ie when you have a portfolio of services and applications to deliver what are the consideratons to be able to deliver them so that management of the platform also scales in a cost-effective way? Much of this is addressed by the concept of a Service Delivery Platform (SDP). In telcos, SDP is a key consideration in managing next-generation services but the actual functionality varies widely by vendor.
The Microsoft SaaS Architecture Strategy Team is now working on the architecture of a service delivery platform for hosters and ISV's managing multiple SaaS applications. This would aim to address common services infrastructure and processes like identity, monitoring, provisioning etc and illustrates the opportunity for deep partnerships between hosters and SaaS ISV's. There is an initial article on this topic in The Architecture Journal and the team is planning to develop a reference implementation based on this and feedback from hosters, ISV's and enterprise SaaS providers.
In a world of Software + Services these hosted service delivery platforms are quickly emerging as a new category of application server. I'm watching with interest what the Windows Live team roll-out within 'Cloud Infrastructure Services' and how we'll architect and expose our own cloud platform for cost-effective service and application delivery on a mass-scale.