If your code needs to access any resources that are outside of your account, this can also introduce new challenges. Any externally accessed resource would need to be running within the scope of some other account. And, as a rule of thumb, accounts have very intentional and hard boundaries to secure the resources in each account. So, then, you’d have to wander into the universe of authorizing cross-account access to enable your system to interact with any resource that lives outside of a tenant account.
Generally, I would stick with the assumption that, in a full stack silo model, your goal is to have all tenant’s resources in the same account. Then, only when there’s a compelling reason that still meets the spirit of your full stack silo, consider how/if you might support any centralized resources.
Onboarding Automation
The account-per-tenant silo model adds some additional twists to the onboarding of new tenants. As each new tenant is onboarded (as we’ll see in Chapter 4), you will have to consider how you’ll automate all the provisioning and configuration that comes with introducing a new tenant. For the account-per-tenant model, our provisioning goes beyond the creation of tenant infrastructure–it also includes the creation of new accounts.
While there are definitely ways to automate the creation of accounts, there are aspects of the account creation that can’t always be fully automated. In cloud environments, however, there are some intentional constraints here that may restrict your ability to automate the configuration or provisioning of resources that may exceed the default limits for those resources. For example, your system may rely on a certain number of load balancers for each new tenant account. However, the number you require for each tenant may exceed the default limits of your cloud provider. Now, you’ll need to go through the processes, some of which may not be automated, to increase the limits to meet the requirements of each new tenant account. This is where your onboarding process may not be able to fully automate every step in a tenant onboarding. Instead, you may need to absorb some of the friction that comes with using the processes that are supported by your cloud provider.
While teams do their best to create clear mechanisms to create each new tenant account, you may just need to allow for the fact that, as part of adopting an account-per-tenant model, you’ll need to consider how these potential limit issues might influence your onboarding experience. This might mean creating different expectations around onboarding SLAs and better managing tenant expectations around this process.
Scaling Consideration
I’ve already highlighted some of the scaling challenges that are typically associated with the full stack silo model. However, with the account-per-tenant model, there’s another layer to the full stack silo scaling story.
Generally speaking, mapping accounts to tenants could be viewed as a bit of an anti-pattern. Accounts, for many cloud providers, were not necessarily intended to be used as the home for tenants in multi-tenant SaaS environments. Instead, SaaS providers just gravitated toward them because they seemed to align well with their goals. And, to a degree, this makes perfect sense.
Now, if you have an environment with 10s of tenants, you may not feel much of the pain as part of your account-per-tenant model. However, if you have plans to scale to a large number of tenants, this is where you may begin to hit a wall with the account-per-tenant model. The most basic issue you can face here is that you may exceed the maximum number of accounts supported by your cloud provider. The more subtle challenge here shows up over time. The proliferation of accounts can end up undermining the agility and efficiency of your SaaS business. Imagine having hundreds or thousands of tenants running in this model. This will translate into a massive footprint of infrastructure that you’ll need to manage. While you can take measures to try to streamline and automate your management and operation of all these accounts, there could be points at which this may no longer be practical.
So, where is the point of no return? I can’t say there’s an absolute data point at which the diminishing returns kicks in. So much depends on the nature of your tenant infrastructure footprint. I mention this mostly to ensure that you’re factoring this into your thinking when you take on an account-per-tenant model.
