Multitenancy¶
When designing a multi-tenant application, various architectural decisions must be made to ensure optimal performance, data isolation, and scalability. One of the most critical choices is how to handle tenant data. Developers can opt for either a shared database model or a database-per-tenant approach, each with its own set of trade-offs.
Shared Database Model¶
In a shared database model, all tenants use the same database instance and schema. Tenant-specific data is identified by including a tenant_id column in each table or dataset. This design is common in relational databases and even in non-relational setups, like document stores or event stores.
Pros:
- Simplicity: Managing a single database instance means fewer moving parts. When changes are made to the schema or application code, they can be deployed and updated across all tenants simultaneously.
Cons:
- Data leakage risk: If proper precautions are not taken, there’s a possibility of one tenant accidentally accessing another tenant’s data. One way to mitigate this risk is to use a query filter mechanism (e.g., in an ORM like Entity Framework) to automatically append tenant-specific filtering to every query.
- Noisy neighbors: Multiple tenants sharing the same database can lead to performance degradation. If one tenant has high resource usage, it may negatively impact others. Rate limiting or assigning different database users for each tenant can help alleviate this issue.
Database-Per-Tenant Model¶
In the database-per-tenant model, each tenant has its own isolated database. The application identifies the tenant and connects to the corresponding database based on the tenant’s identity.
Pros:
- Isolation: Each tenant’s data and performance are completely isolated from others. Noisy neighbors and data leakage risks are significantly minimized.
Cons:
- Infrastructure complexity: Managing a separate database for each tenant can lead to increased complexity, especially in cases of schema changes. Every schema change must be applied to each tenant’s database, which can become cumbersome as the number of tenants grows. Automation tools can help manage schema updates across databases.
Hybrid Model¶
A hybrid approach combines elements from both shared and isolated models. For instance, some tenants may share a database, while others have isolated instances. This strategy provides flexibility in balancing isolation with simplicity, depending on the needs of specific tenants.
Pros:
- Scalability and flexibility: Tenants with lower resource demands can share infrastructure, while those with higher requirements or specific privacy needs can have dedicated databases or application instances.
Cons:
- Complexity: Managing such a hybrid system requires careful planning to avoid overwhelming the infrastructure with too many custom configurations and isolated instances. Additionally, global identifiers (e.g., globally unique customer IDs) are recommended to avoid conflicts when migrating tenants across different database instances.
Considerations¶
When designing a multi-tenant system, several factors should influence your decision:
- Number of tenants: As the number of tenants increases, the complexity and cost of maintaining isolated databases may become prohibitive.
- Data volume and performance: Applications with high data volume or resource-intensive queries may require database isolation to prevent performance issues due to noisy neighbors.
- Security and privacy: Applications handling sensitive data may prioritize database-per-tenant setups to ensure stricter isolation.
- Operational overhead: The shared database model can simplify deployment and schema updates, but it may require additional safeguards like automated query filters or rate-limiting mechanisms.
Page last modified: 2024-09-16 11:45:04