Multi-Tenancy in SaaS
Every SaaS application must isolate customer data. The multi-tenancy pattern you choose affects security, performance, cost, and complexity. Laravel's flexibility lets you implement any strategy, but picking the right one early saves painful migrations later.
Multi-tenancy is not just a database concern—it affects caching, file storage, queues, and even logging. A well-architected multi-tenant system isolates all of these layers so that one tenant's data never leaks into another tenant's experience. The three primary strategies differ in how they achieve this isolation and the trade-offs they accept.
Strategy 1: Single Database, Tenant Column
Add a tenant_id column to every table. Apply a global scope on all models so queries automatically filter by the authenticated tenant. This is the simplest approach—one database, one deployment—but tenant data lives side by side, making compliance audits harder.
Implementation is straightforward: create a BelongsToTenant trait that adds a global scope filtering by tenant_id and automatically sets the column on creation. Apply this trait to every model that contains tenant data. The global scope ensures that even if a developer forgets to add a where clause, the query still filters by tenant.
The downside is that a single misbehaving query—a raw query without the scope, an admin tool that bypasses scopes—can expose data across tenants. Rigorous code review and comprehensive testing are essential. Use database-level row security policies (available in PostgreSQL) as an additional safety net.
Strategy 2: Separate Databases
Each tenant gets their own database. Configure dynamic database connections in Laravel's DatabaseManager. Run migrations per tenant with a custom Artisan command. This provides complete isolation and makes it straightforward to move a high-traffic tenant to dedicated infrastructure.
The operational overhead is significant: managing hundreds or thousands of databases requires automation for backups, migrations, and monitoring. Use a central "landlord" database to store tenant metadata and connection details. When a request arrives, resolve the tenant from the subdomain or header, look up their database connection, and configure Laravel to use it for the duration of the request.
Strategy 3: Schema-Based Isolation
On PostgreSQL, create a separate schema per tenant within a single database. Switch the search path at the middleware level. This balances isolation with operational simplicity—fewer databases to back up, but logical separation at the schema layer. Each tenant's tables exist in their own namespace, preventing accidental cross-tenant queries.
Tenant Resolution
Resolve tenants via subdomain (acme.yourapp.com), path prefix (yourapp.com/acme), or custom header. Use middleware to set the current tenant in a singleton and apply it throughout the request lifecycle. The resolution strategy affects your DNS configuration, SSL certificate management, and routing setup.
Subdomain resolution is the most common for B2B SaaS: each customer gets a branded URL, and wildcard DNS plus wildcard SSL certificates handle routing automatically. For single-page applications, a custom header or JWT claim can carry the tenant identifier, keeping the URL clean.
Caching and File Storage
Cache keys must include the tenant identifier to prevent data leakage. Prefix all cache keys with tenant_{id}_ or use separate Redis databases per tenant. For file storage, organize uploads under tenant-specific directories: storage/tenants/{id}/uploads/. Configure Laravel's filesystem to dynamically resolve the base path based on the current tenant.
Billing and Feature Flags
Integrate Stripe or Paddle via Laravel Cashier to manage subscriptions per tenant. Use feature flags to gate premium functionality. Store plan limits in the tenant model—maximum users, storage quota, API rate limits—and enforce them in policy classes and middleware. When a tenant exceeds their plan limits, show a clear upgrade prompt rather than a cryptic error.
Testing Multi-Tenant Applications
Write feature tests that act as different tenants within the same test suite. Use database transactions to keep tests fast and isolated. The most critical test in any multi-tenant application: verify that Tenant A can never access Tenant B's data. Create two tenants, create data for each, authenticate as Tenant A, and assert that Tenant B's data is invisible. Run this test for every model, every API endpoint, and every admin action.
Conclusion
Choose single-database tenancy for simplicity and cost efficiency when you have many small tenants. Choose separate databases when compliance, security, or performance isolation are non-negotiable. Schema-based isolation offers a middle ground for PostgreSQL users. Whichever strategy you choose, invest heavily in testing and automation—the cost of a tenant data leak far exceeds the cost of thorough engineering.
0 Comment