There are totally 4 maturity models/levels in which you can deliver a SaaS application/product.
In a single tenant model each of the tenants will get their own respective instances. There is absolutely no sharing of anything (code, DB, etc.). Each time a new customer (tenant) is added a new (logical) hardware is provisioned and new instance of the product is setup in the allocated environment. This could also be a logical separation of the hardware in the form of separate web sites within the same IIS server. Single tenant model is also commonly referred as Hosted model.
Maturity Level 1 and 2 falls under single tenant model. In both the levels the tenant gets their own instance of the software. However, the primary difference between these levels is that in Level 1 you may even have a customized code base for that particular tenant. Therefore, you may even end up having different code bases for each tenant (as depicted with multiple colors in the above picture). However, from a Tenant’s perspective it’s immaterial whether it’s Level 1 or 2 as long as the software performs the expected functions.
- Takes less time to roll-out in to SaaS model, since the product does not require going through any changes to support SaaS model.
- Overall SaaS transition complexity and cost is going to be less.
- Does not require any SaaS Architecture/Engineering expertise. All that is required would be expertise on the hardware front, which is any addressed by IaaS vendors.
- Level 1 offers a unique advantage of the ability to provide customized versions to your client. However, this could also be viewed as a disadvantage as you will have to keep maintaining several versions of your product.
- Supports non-web native applications. For example, you can use windows citrix to deliver a desktop or client/server application (ex: applications developed in VB) in a SaaS model.
- Certain market/customer base does not like the idea of multi-tenancy. For example: a banking customer will not like the idea of sharing their data/environment with other banking organizations. In some cases the security compliance also does not allow sharing. In these instances Single Tenant wins over multi-tenant.
- Maintenance efforts are going to be huge as you will have to maintain multiple code base/environments. For example, if you are going to make a fix then you will have to roll-it out ‘n’ number of times, where n is the number of tenants supported.
- Operational costs are going to be extremely high, particularly over the long run.
Multi-Tenancy is an architecture capability that allows an application/product to recognize tenants (tenants could be users, group of users or organizations) and exhibit functionalities as per the configuration set for the tenants. An on-premise application is typically designed to work for a single organization. Therefore, the very concept of making an on-premise application realize/operate in the context of a particular tenant is a big change. Every single functionality in the product has to be tweaked in order to achieve multi-tenancy. Segregation at the data layer is another big challenge. There are various degrees of multi-tenancy that can be supported. The complexity/effort also depends on the multi-tenancy degree that you are choosing to go with.
Maturity Level 3 and 4 fall under the multi-tenant model. Level 3 and 4 differ only in the level of scalability they can offer. Level 3 is more of a scale-up solution where you can upgrade the hardware to increase the number of tenants that can be supported. Level 4 supports scale-out solution where multiple hardwares can be added so that a load balanced environment can be created. As you can imagine, the decision between Level 3 and Level 4 lies with the amount of tenants that you are expecting to have on the system.
- Facilitates a cost effective way of delivering SaaS solution.
- Huge savings in operational cost, particularly over the long run. This in turn will allow the ISVs to offer an attractive pricing to their customers, therefore creating a snow ball effect.
- Enables to achieve higher levels of customer satisfaction.
- Roll-out of upgrades/fixes is much easier.
- Easier to adopt/implement best practices in the product features as you will be concentrating on only one version of the product.
- The design principles of a multi-tenant system offer a high level of maintainability. For example, if a customer requests for few additional fields in one of the pages you can easily add them through custom field’s module.
- Scalability to expand the number of tenants. For example: Salesforce.com has more than 100,000 tenants running on their multi-tenant system. Can you even imagine how this will work in a single tenant model?
- Due to the amount of changes that has to happen in the product it takes a while to roll-out the solution.
- Initial investment to enable multi-tenancy is high. While you will recover this cost in the form of savings in operational expenses it still requires that initial investment and as well the risk involved in achieving the expected business growth.
- Requires SaaS architecture expertise, which may not be within the company. Will have to find a strong SaaS partner to guide you in the transition process.
As you can see each model has its own advantage and disadvantages. Hence, it’s extremely important to think through for a given business/domain/product to understand if multi-tenancy is really required or not. In my next blog I will talk about how to objectively make this decision.
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