Virtualization vs. multi-tenant architecture

For software developers, SaaS is typically associated with "multi-tenant architecture", which many believe is a prerequisite for a SaaS application.

Traditionally, there would be only one instance of an application running on a server, and this instance would only serve one customer a.k.a. tenant. In the SaaS world, giving each tenant a dedicated server is a huge waste of resources and service providers want to put as many customers on the same server as possible. However, many applications (on Windows – most applications), by design, cannot have multiple instances on the same server.

To solve this problem, software developers came up with "multi-tenant architecture". The application is redesigned in such a way that a single physical copy of an application provides multiple "virtual" instances – each tenant gets an instance. Compared to several independent instances, using the same physical instance allows extensive sharing of data and metadata between instances/tenants

Multi-tenant design is considered to be more efficient than multi-instancing, but in reality, as always, your mileage will vary. And to make the estimation process easier, I'd like to shed some light – from the ISV's point of view – on the "dark side" of the multi-tenant approach:

• Cost of transition – There are no good recipes for converting a traditional single-tenant application to multi-tenant design. Empirical data shows that typically the process takes 12+ months and requires resources of nearly the entire development organization. The existing feature development is essentially frozen.
  
• Ongoing costs – Current generation of software – development tools, middleware, management tools – do not natively support multi-tenant paradigm. For traditional applications, mundane development tasks were taken care of by frameworks and tools, and mundane management tasks were taken care of by management solutions. None of this software natively supports multi-tenant paradigm, so an ISV will have to develop a lot of plumbing-ware from scratch.
  
• Skills mismatch – The ISV must deliver complex services outside their area of expertise – hosting, SLA enforcement, monitoring, data protection, security, etc. The expertise associated with running a large-scale datacenter is not something that can be acquired overnight.
  
• Limited customization – It's very hard to efficiently implement per-tenant database schema customization in a single database, and it's not possible to use standard DBMS tools – like built-in indexing. Plus, the multi-tenant application cannot use script-based customization of the internal logic – what if a buggy script loops infinitely?
  

  SmoothSpan Bob Warfield and Unreasonable Men argued that customization capabilities are often excessive and there is little harm in removing much of that flexibility. For newly written applications, it might even be true. But if an ISV has a customer base to migrate to SaaS model, telling customers that their solutions will be broken because some of the customizations don't work anymore is hardly an option.
  

• Weak isolation – Because all tenants run inside the same application instance, one tenant can bring down everyone else on the same machine – due to a security breach, memory leak, "infinite loop" bug – you name it. It is technically possible to build some resource management capabilities into the application itself, but the existing development tools – languages, frameworks – do not support safe multi-tenancy and hence don't provide resource management capabilities.
  
• Inflexible service levels – Finally, lack of resource management means that you cannot provide and hence monetize service level guarantees.
  

Virtualization – The silver-coated bullet

There is no silver bullet, but in this case, there is a silver-coated one.
Virtualization technology provides a solution to all the problems mentioned – put the application in a virtual environment and ship it – in unchanged state – to the service provider's datacenter. If the front-end is not web-based, use a VPN. This topic has already been discussed by Bob Warfield and Phil Wainewright who cites a real success story. Hardware virtualization, with single-digit real-life consolidation ratio, will probably not be good enough. But a light-weight server virtualization technology that can host 100+ instances on a single server - Virtuozzo – provides very cost-effective solution. Even if you are very determined to pursue multi-tenancy, Virtuozzo will buy you enough time to make the transition smooth and successful. However, in the majority of cases, further transition will not even be necessary because the Virtuozzo-based solution works well for most customers.

Shameless plug – check out my SaaS blog.

Comments on Gartner Top 10 technology list

Just before its annual symposium event, Gartner published a list of the Top 10 strategic technologies in 2008. We wanted to add our perspective because SWsoft plays is a significant role in three of those areas. We welcome your comments with your perspective.

Green IT – Higher density means fewer servers and the lowest possible power consumption. Virtuozzo providers several times higher density – number of workloads running on a single server – as compared with VMware or XEN. Take a look at the
customer testimonies here.

Virtualization 2.0 – According to Gartner, 2.0 means supplementing virtualization technology with automation – which is exactly what SWsoft has been delivering since 1999. In fact, back in 1999, Virtuozzo was developed as a part of our automation suite. Many virtualization companies started with solving an interesting engineering problem of virtualizing a non-virtualizeable computer architecture. Now, as they have the hammer, they are looking for the nails. At SWsoft, we first looked at the issues in the large scale data centers and then created a solution, where virtualization and automation work together.

Web Platform and WOA - This is a real 2.0 for us – SWsoft 2.0, if you will. We are trying, with our Open Fusion initiative and a set of SaaS enabling technologies, to help transform the web hosting industry into a SaaS delivery industry. It seems our message of automation and virtualization as equally important pillars of the SaaS infrastructure is finally getting through. However, there is a lot more work ahead to make the transformation a reality.

Virtuozzo for Amazon

I just read that Xen-based Amazon EC2 suffered major faults, and based on the information provided, I think that Virtuozzo can be a perfect solution for Amazon:

• Very easy to build high-availability solution – no lost data
  
• Zero performance overhead and much higher hardware and power efficiency – several times more environments on the same server
  
• Strong security isolation – virtual environments can't see each other's data
  
• Resource management – when some application starts misbehaving, other tenants remain unaffected. CPU, memory, network bandwidth – everything can be throttled dynamically
  

Virtuozzo was specifically designed to meet the extremely high – and ever increasing – performance and isolation standards of service providers and large-scale datacenters, not as technology for consolidating a few legacy applications on a single server. And it has been used this way successfully since 1999.

Some of our customers shared their experiences – take a look. Perhaps it's time for Amazon to take a closer look at Virtuozzo.