Saas Multitenancy

SaaS Multi-Tenancy

Capability

Implement robust multi-tenant architecture for SaaS applications with proper data isolation, tenant context management, and scalable patterns. Covers shared database with row-level security, tenant-scoped queries, and organization/team hierarchies.

Use Cases

• Data isolation between tenants (organizations/workspaces)
• Team/organization hierarchy with roles
• Tenant-scoped API endpoints
• Subdomain or path-based tenant routing
• Tenant provisioning and onboarding
• Cross-tenant admin operations

When NOT to use this skill

This skill covers shared-database multi-tenancy with row-level security, tenant-scoped queries, and org/team hierarchies. It is not the right fit for:

• Single-tenant deployments (one customer per environment, separate DB per customer). RLS-based shared-DB patterns are overkill; use plain auth and treat the database as private.
• Per-customer database isolation (fully separate DB instances per tenant). Different patterns; closer to fleet management. Use a multi-DB orchestrator.
• Per-record customer-managed encryption keys (BYOK). Adds an orthogonal cryptography layer; the RLS patterns here do not address encryption.
• Multi-region tenant sharding. Patterns here assume one logical database. Sharding needs different tooling (Citus, Vitess, custom routing).

Patterns

Row-Level Security (RLS) Pattern

When to use: Shared database with multiple tenants needing data isolation

Implementation: Use database-level RLS policies to enforce tenant isolation. Every query automatically filters by tenant.

-- Enable RLS on tenant tables
ALTER TABLE projects ENABLE ROW LEVEL SECURITY;

-- Create tenant isolation policy
CREATE POLICY tenant_isolation ON projects
  USING (tenant_id = current_setting('app.current_tenant_id')::uuid);

-- Create policy for insert
CREATE POLICY tenant_insert ON projects
  FOR INSERT
  WITH CHECK (tenant_id = current_setting('app.current_tenant_id')::uuid);

-- Create policy for update/delete
CREATE POLICY tenant_modify ON projects
  FOR ALL
  USING (tenant_id = current_setting('app.current_tenant_id')::uuid);

// Middleware to set tenant context
async function setTenantContext(tenantId: string) {
  // Set session variable for RLS
  await db.execute(
    sql`SELECT set_config('app.current_tenant_id', ${tenantId}, true)`
  );
}

// Usage in API route
async function handleRequest(req: Request) {
  const tenantId = await getTenantFromSession(req);
  await setTenantContext(tenantId);

  // All subsequent queries automatically filtered
  const projects = await db.query.projects.findMany();
  return projects; // Only returns tenant's projects
}

Tenant Context Middleware

When to use: Every request needs tenant context for data access

Implementation: Extract tenant from subdomain, path, or session and inject into request context.

// Tenant context middleware
async function tenantMiddleware(req: Request, next: NextFunction) {
  // Strategy 1: Subdomain (acme.app.com)
  const subdomain = req.headers.host?.split('.')[0];

  // Strategy 2: Path (/org/acme/dashboard)
  const pathTenant = req.url.match(/^\/org\/([^\/]+)/)?.[1];

  // Strategy 3: Session/JWT claim
  const sessionTenant = req.session?.tenantId;

  const tenantSlug = subdomain || pathTenant || sessionTenant;
  if (!tenantSlug) {
    throw new UnauthorizedError('Tenant context required');
  }

  // Resolve tenant
  const tenant = await db.query.tenants.findFirst({
    where: eq(tenants.slug, tenantSlug)
  });

  if (!tenant) {
    throw new NotFoundError('Tenant not found');
  }

  // Inject into request context
  req.tenant = tenant;
  req.tenantId = tenant.id;

  // Set database context for RLS
  await setTenantContext(tenant.id);

  return next();
}

Organization Hierarchy

When to use: Tenants with teams, departments, or nested groups

Implementation: Create organization → team → member hierarchy with role-based permissions.

// Schema for org hierarchy
const organizations = pgTable('organizations', {
  id: uuid('id').primaryKey().defaultRandom(),
  name: text('name').notNull(),
  slug: text('slug').unique().notNull(),
  plan: text('plan').default('free'),
  createdAt: timestamp('created_at').defaultNow()
});

const teams = pgTable('teams', {
  id: uuid('id').primaryKey().defaultRandom(),
  organizationId: uuid('organization_id').references(() => organizations.id),
  name: text('name').notNull(),
  createdAt: timestamp('created_at').defaultNow()
});

const memberships = pgTable('memberships', {
  id: uuid('id').primaryKey().defaultRandom(),
  userId: uuid('user_id').references(() => users.id),
  organizationId: uuid('organization_id').references(() => organizations.id),
  teamId: uuid('team_id').references(() => teams.id),
  role: text('role').notNull(), // 'owner' | 'admin' | 'member'
  createdAt: timestamp('created_at').defaultNow()
});

// Check permission
async function checkPermission(userId: string, orgId: string, requiredRole: string) {
  const membership = await db.query.memberships.findFirst({
    where: and(
      eq(memberships.userId, userId),
      eq(memberships.organizationId, orgId)
    )
  });

  if (!membership) return false;

  const roleHierarchy = { owner: 3, admin: 2, member: 1 };
  return roleHierarchy[membership.role] >= roleHierarchy[requiredRole];
}

Tenant Provisioning

When to use: Creating new tenant/organization during signup

Implementation: Atomic tenant creation with default resources.

async function provisionTenant(
  ownerUserId: string,
  orgName: string
) {
  return await db.transaction(async (tx) => {
    // 1. Generate unique slug
    const baseSlug = slugify(orgName);
    const slug = await generateUniqueSlug(baseSlug);

    // 2. Create organization
    const [org] = await tx.insert(organizations).values({
      name: orgName,
      slug,
      plan: 'free'
    }).returning();

    // 3. Create owner membership
    await tx.insert(memberships).values({
      userId: ownerUserId,
      organizationId: org.id,
      role: 'owner'
    });

    // 4. Create default team
    const [defaultTeam] = await tx.insert(teams).values({
      organizationId: org.id,
      name: 'General'
    }).returning();

    // 5. Add owner to default team
    await tx.update(memberships)
      .set({ teamId: defaultTeam.id })
      .where(
        and(
          eq(memberships.userId, ownerUserId),
          eq(memberships.organizationId, org.id)
        )
      );

    // 6. Initialize default resources
    await initializeDefaultResources(tx, org.id);

    return org;
  });
}

Stack Implementations

{{stack.frontend.framework}} + {{stack.backend.database}}

Supabase RLS:

-- Supabase-specific RLS with auth.uid()
CREATE POLICY "Users can view own org data" ON projects
  FOR SELECT USING (
    organization_id IN (
      SELECT organization_id FROM memberships
      WHERE user_id = auth.uid()
    )
  );

Prisma Multi-tenant:

// Prisma client extension for tenant scoping
const prismaWithTenant = (tenantId: string) => {
  return prisma.$extends({
    query: {
      $allModels: {
        async $allOperations({ args, query }) {
          args.where = { ...args.where, tenantId };
          return query(args);
        }
      }
    }
  });
};

Exit Criteria

Before declaring this skill's work complete, run each check below and paste the output. "Looks right" is not sufficient. Items marked gateable can be wired into project/gates/ for automated phase-exit checks.

If any check fails, do not declare done. Fix and re-run.

Anti-Patterns (Excuse / Rebuttal)

Excuse: "I'll take the tenant ID from the request body; the client knows which tenant they're in."

Rebuttal: The client can send any tenant ID, including ones they do not belong to. This is the cross-tenant data leak pattern. Derive tenant from the authenticated session, never from the request body or query string.

// WRONG: Client can send any tenant ID
const projects = await getProjects(req.body.tenantId);

// RIGHT: Derive tenant from authenticated session
const tenantId = req.session.tenantId;
const projects = await getProjects(tenantId);

Excuse: "Background jobs run server-side; they don't need tenant context."

Rebuttal: They absolutely do, and forgetting it is the second-most-common multi-tenant data leak. A job that queries analytics without setting tenant context returns all tenants' analytics, then sends them to one tenant's email. Pass the tenant ID into the job payload, restore the context inside the worker.

// WRONG: No tenant context in async job
queue.process('sendReport', async (job) => {
  const data = await db.query.analytics.findMany(); // Gets ALL data!
});

// RIGHT: Pass and restore tenant context
queue.process('sendReport', async (job) => {
  await setTenantContext(job.data.tenantId);
  const data = await db.query.analytics.findMany(); // Tenant-scoped
});

Excuse: "The cache key is the same for every tenant; the data is the same shape."

Rebuttal: The shape may be the same; the data is not. Without a tenant namespace, tenant A's dashboard stats serve to tenant B until the TTL expires. Always namespace cache keys by tenant.

// WRONG: Cache key collision across tenants
await cache.set('dashboard-stats', stats);

// RIGHT: Namespace cache keys by tenant
await cache.set(`tenant:${tenantId}:dashboard-stats`, stats);