What You Need to Know About SaaS: Architecture, Types, and Multi‑Tenant Strategies

1 Cloud Service Architecture Concepts

1.1 PaaS

Platform-as-a-Service provides a middleware layer where developers use provided languages and tools (e.g., Java, Python, .NET) to deploy applications on the provider's cloud infrastructure. Customers do not manage underlying resources such as networks, servers, OS, or storage, but they control the deployed applications and their runtime configuration.

1.2 IaaS

Infrastructure-as-a-Service offers compute, memory, storage, and networking resources that users can provision and run any software on, including operating systems and applications. Consumers do not control the physical infrastructure but can choose OS, storage size, and may have limited control over network components like routers or firewalls.

1.3 SaaS

Software-as-a-Service delivers applications running on cloud infrastructure that users access via browsers or client interfaces on any device. Consumers do not manage any underlying cloud resources. Typical examples include DingTalk, WeChat Work, and other enterprise SaaS products covering OA, ERP, CRM, etc.

2 Two Major Features of SaaS Systems

Deployed on the provider's servers rather than the customer's own servers.

Subscription‑based model where customers select needed functions, pay for usage, and can be billed by service time.

3 Differences Between SaaS, Traditional Software, and Internet Application Providers

3.1 SaaS Services

Located between traditional and pure internet services, SaaS is offered on a rental basis. The server and software belong to the provider; users pay for usage rights after registration.

3.2 Traditional Software

Software and accompanying hardware are sold and installed on the customer's own servers or designated cloud servers. Revenue comes from software sales and related maintenance services.

3.3 Internet Application Providers

Servers are deployed in the cloud; all users register and use the service via client applications. Revenue is generated through ads and paid value‑added services.

4 B2B2C

SaaS as a tenant system must provide registration, purchase, and business entry for end‑users (C‑side) while also offering tenant management, traffic monitoring, and service status monitoring for the B‑side (operations/maintenance).

5 SaaS System Classification

5.1 Business‑Oriented SaaS

Provides tools and services that directly support customers' revenue‑generating activities, such as e‑commerce platforms (Youzan, Weimob) and sales CRM for B2B2C enterprises. In later stages, products expand to multi‑scenario and multi‑industry solutions.

5.2 Efficiency‑Oriented SaaS

Focuses on tools that improve operational efficiency, such as project management or video‑conference solutions (e.g., Zoom). These products address common workflow problems across enterprises.

5.3 Hybrid SaaS

Combines business and efficiency features, such as WeChat Work, which offers collaboration tools while also providing private‑domain management capabilities for enterprises.

6 How to SaaSify

Deploy to the cloud and upgrade performance to support larger user scales.

Refactor the user system to support C‑side logins (phone, mini‑program, SMS verification).

Implement gateway services, rate limiting, and request tampering protection.

Develop tenant management (basic info, resource binding, service periods).

Adapt the client (usually web) with page‑level permission control based on tenant resources.

Build a website with pricing, trial, selection, and payment functions.

Modify backend APIs for tenant‑level data permission control.

7 Core Components of a SaaS Product

Security component: System security is the top priority.

Data isolation component: Ensures that data between tenants remains invisible to each other.

Configurable component: Allows tenants to customize UI layout, theme, logo, etc.

Scalable component: Supports horizontal scaling via load balancers and container technologies.

Zero‑downtime upgrade: Enables upgrades without restarting the application.

Multi‑tenant component: Guarantees data isolation and correct indexing for each tenant.

8 SaaS Multi‑Tenant Architecture

8.1 Core Concepts

Tenant: An enterprise or individual customer; data and behavior are isolated between tenants.

User: An individual within a tenant who logs in with credentials.

Organization: The internal structure of an enterprise tenant.

Employee: A specific staff member within an organization.

Solution: A packaged set of products and services addressing a specific business problem.

Product capability: Features sold to customers that enable end‑to‑end scenario solutions.

Resource domain: A set of cloud resources used to run one or more product applications.

Cloud resource: Compute, storage, network, or container resources provided by cloud platforms (Alibaba Cloud, Tencent Cloud, Huawei Cloud, etc.).

8.2 Three Multi‑Tenant Models

8.2.1 Vertical Isolation Model

Advantages: strong isolation, simple billing, reduced fault impact.

Disadvantages: scalability challenges, higher cost per tenant, slower agile iteration, complex unified monitoring.

8.2.2 Shared Model

Advantages: efficient management, lower infrastructure cost.

Disadvantages: tenant performance interference, more complex tenant‑level billing.

8.2.3 Domain Isolation Model

8.3 Capabilities Required for Multi‑Tenant Systems

Support shared or dedicated cloud resources across tenants.

Provide data and behavior isolation with domain‑level access control.

Enable organization‑based management and capability authorization within a tenant.

Allow different product capabilities to run on distinct cloud resources as needed.

8.4 Multi‑Tenant System Architecture Diagram