multi-tenant or multi-Instance

Multi-Tenant vs. Multi-Instance ​

​multi-tenant
​Major advantages:
Better profitability.
Using the same infrastructure and resources will cost you less because the resources will be shared between your customers.
Simplicity related to shared infrastructure.
Since there is only one infrastructure, it is easier to maintain.
Save time:
This type of architecture has the advantage of being simpler to set up than a multi-instance architecture. This makes it easier to develop your SaaS application and requires less time and resources to maintain it.
Always up-to-date:
Updates will only be done once so that they will benefit all of your users.
Disadvantages:
Shared database:
Any action affecting the database will affect all shared clients.
So it is at the application level that data separation will have to be done and therefore the developer team will prevent data exposure from one customer to another, which will increase the complexity of the application layer.
Any security breach has a massive effect because it will affect all users of the system.
Less customizable:
You will be less easily able to customize the offer you offer to your customers. It is still possible to lock some features in the code of the application but again, it may lead to complexity related to development.

multi-instance
​What are the benefits of multi-instance
Data Isolation:
Each organization (or team) has its own database and infrastructure. This results in total data isolation and offers a guarantee of confidentiality for your customers. Hackers will therefore have less interest in attacking your system because they will be less interested in recovering access from a small segment of your total data.
Simplified scalability:
Increasing resources is easier for a customer because only its infrastructure will need to be modified. We will be able to allocate more CPU, RAM or storage according to their needs.
Increase in overall availability:
If an instance fails for some reason, this issue will not affect all of your customers.
Personalisation:
Each of your customers can receive customizations of your SaaS (dedicated features, scheduled updates, etc...) that you can easily turn into business arguments.
What are the negative points of multi-instance
More complicated to deploy and maintain:
As you understand, each of your customers has their own dedicated infrastructure, you will need to provision each infrastructure, maintain it and update it separately.
Higher total cost:
This choice of architecture is less cost-effective when it comes to creating and configuring each environment such as the database or application because costs are not shared.

​Which architecture is best for iPaaS?

As we have discussed, each architecture has its own merits and downsides. However, in regard to using an iPaaS solution, a multi-instance architecture provides users with much greater control.
In this environment, iPaaS can be configured, controlled and managed by either the customer or the provider, which will help with complex business integrations and data processing.
As iPaaS is potentially integrating many business applications and converting, transforming and synchronising data from these multiple systems and locations, having an isolated database makes it easier to manage – especially if the data needs migrating from one system to another.
It also provides better scalability as it will be easier to add new applications and tweak business processes as the business grows
 
https://www.codelessplatforms.com/blog/multi-tenant-vs-multi-instance/
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Which architecture is best for SaaS?

​To summarize, for my part, if I had a “fast time-to-market” problem and need to quickly develop a SaaS solution, I would rather focus on a multi-tenant architecture because it is easier to set up.
On the other hand, if I needed to develop a more robust and secure solution, I would instead opt for a multi-instance architecture and benefit from total data isolation.

​To go further, build your architecture with Kubernetes

​Kubernetes has the advantage of allowing you to build a multi-instance architecture as well as multi-tenant architecture. But if following Kubernetes recommended architectures :
 

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​Technical Short Response

​As all information from above is used in the trade off : Technically we should look at the multi-Instance architecture. 

Functional , Release and  Infrastructure trade-offs ​

​Functional
Functional there is a small gain as personalisation can be done ( css, images, … ) as long as they are kept outside the releases/deploys
Release
Release management is a little harder as we have to ensure that all instance-versions are managed

• 1 version for all?
• Support of different Versions?

Infrastructure
For infrastructure there is a higher cost of selecting the Multi-Instance as here we need to use different instances of every layer ( as shown in the images above this means that we are going to use multiple databases ). we are going to see a higher pricing and management as different instances have to be requested, maintained and paid.