How to build multi-tenancy in PostgreSQL for developing SaaS applications?

Building multi-tenancy in PostgreSQL for SaaS applications can be achieved through several approaches, each with its own advantages and trade-offs. Here are the main strategies for implementing multi-tenancy in PostgreSQL:

Shared Database, Shared Schema

In this approach, all tenants share the same database and schema, with a tenant identifier column used to distinguish between different tenants' data.

• Add a tenant_id column to all tables that contain tenant-specific data
• Use Row-Level Security (RLS) policies to enforce data isolation between tenants
• Implement database roles and permissions to manage access control

Example RLS policy:

CREATE POLICY tenant_isolation_policy ON mytable
    USING (tenant_id = current_setting('app.current_tenant')::uuid);

Pros:

• Efficient resource utilization
• Easier maintenance and updates
• Simplified backup and restore processes

Cons:

• Potential for data leakage if not implemented correctly
• May require more complex application logic to handle tenant isolation

Shared Database, Separate Schemas

This model uses a single database but creates a separate schema for each tenant.

• Create a new schema for each tenant
• Use search_path to switch between tenant schemas
• Implement schema-level permissions for access control

Example schema creation:

CREATE SCHEMA tenant_123;
SET search_path TO tenant_123, public;

Pros:

• Better logical separation between tenants
• Easier to implement tenant-specific customizations
• Simplified query structure (no need for tenant_id in WHERE clauses)

Cons:

• Higher operational complexity for schema management
• Potential performance impact with a large number of schemas

Database per Tenant

In this approach, each tenant gets their own dedicated database.

• Create a new database for each tenant
• Use connection pooling to manage multiple database connections

Pros:

• Strongest isolation between tenants
• Easier to meet specific compliance requirements
• Simplified backup and restore per tenant

Cons:

• Higher operational complexity
• Potentially higher infrastructure costs
• Challenges with cross-tenant operations

Hybrid Approach

Combine multiple strategies based on tenant requirements:

• Use shared database/schema for smaller tenants
• Provide dedicated databases for larger tenants or those with specific needs

Pros:

• Flexibility to meet diverse tenant requirements
• Better resource allocation based on tenant needs

Cons:

• Increased complexity in managing different models
• Potential challenges in maintaining consistency across models

Best Practices

1. Use database roles and permissions to enforce access control
2. Implement connection pooling for efficient resource utilization
3. Use prepared statements to improve query performance
4. Regularly monitor and optimize database performance
5. Implement robust error handling and connection validation
6. Consider using extensions like Citus for horizontal scaling of multi-tenant databases

When choosing a multi-tenancy strategy, consider factors such as:

• Number of tenants
• Data volume per tenant
• Regulatory requirements
• Need for tenant-specific customizations
• Operational complexity you can manage

By carefully evaluating these factors and implementing the appropriate multi-tenancy model, you can build scalable and secure SaaS applications using PostgreSQL.

Sources
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