Building a Multi-Tenant SaaS with Stripe and Postgres: Complete Guide

Multi-tenancy is the architecture that lets you serve hundreds of customers from one codebase. Get it wrong and you'll either leak data between tenants or spend weeks refactoring. Get it right and you have a foundation that scales to enterprise.

Here's the complete approach I use — row-level security in Postgres, Stripe for billing, and TypeScript throughout.

The Two Architectures

Before any code: choose your isolation model.

Schema-per-tenant: Each customer gets their own Postgres schema (tenant_abc.users, tenant_abc.orders). Maximum isolation, painful migrations.

Row-level security (RLS): All tenants share tables. Every row has a tenant_id. Postgres enforces isolation at query time. This is what we use.

RLS wins for most SaaS unless you have regulatory requirements for physical data separation.

Database Setup with RLS

-- Every table gets tenant_id
CREATE TABLE users (
  id UUID PRIMARY KEY DEFAULT gen_random_uuid(),
  tenant_id UUID NOT NULL REFERENCES tenants(id),
  email TEXT NOT NULL,
  created_at TIMESTAMPTZ DEFAULT NOW()
);

-- Enable RLS
ALTER TABLE users ENABLE ROW LEVEL SECURITY;

-- Policy: users can only see their tenant's rows
CREATE POLICY tenant_isolation ON users
  USING (tenant_id = current_setting('app.current_tenant_id')::UUID);

-- App role that RLS applies to (not superuser)
CREATE ROLE app_user;
GRANT SELECT, INSERT, UPDATE, DELETE ON users TO app_user;

// Set tenant context before every query
import { Pool } from 'pg';

const pool = new Pool({ connectionString: process.env.DATABASE_URL });

export async function withTenant<T>(
  tenantId: string,
  fn: (client: PoolClient) => Promise<T>
): Promise<T> {
  const client = await pool.connect();
  try {
    await client.query('SET ROLE app_user');
    await client.query(
      `SET LOCAL app.current_tenant_id = '${tenantId}'`
    );
    return await fn(client);
  } finally {
    client.release();
  }
}

// Usage — no manual WHERE tenant_id = ? needed
const users = await withTenant(tenantId, async (client) => {
  const { rows } = await client.query('SELECT * FROM users');
  return rows; // Postgres automatically filters by tenant
});

Stripe Integration for Per-Tenant Billing

Each tenant maps to a Stripe Customer. Subscriptions determine feature access.

import Stripe from 'stripe';

const stripe = new Stripe(process.env.STRIPE_SECRET_KEY!, {
  apiVersion: '2024-12-18.acacia',
});

// Create tenant + Stripe customer atomically
export async function createTenant({
  name,
  email,
  plan,
}: {
  name: string;
  email: string;
  plan: 'starter' | 'pro' | 'enterprise';
}) {
  // Create Stripe customer first
  const stripeCustomer = await stripe.customers.create({
    email,
    name,
    metadata: { plan },
  });

  // Create subscription
  const priceId = PLAN_PRICE_IDS[plan];
  const subscription = await stripe.subscriptions.create({
    customer: stripeCustomer.id,
    items: [{ price: priceId }],
    payment_behavior: 'default_incomplete',
    expand: ['latest_invoice.payment_intent'],
  });

  // Store in DB with Stripe IDs
  const tenant = await db.tenant.create({
    data: {
      name,
      stripeCustomerId: stripeCustomer.id,
      stripeSubscriptionId: subscription.id,
      plan,
      status: 'active',
    },
  });

  return {
    tenant,
    clientSecret: (subscription.latest_invoice as any)
      ?.payment_intent?.client_secret,
  };
}

const PLAN_PRICE_IDS = {
  starter: process.env.STRIPE_STARTER_PRICE_ID!,
  pro: process.env.STRIPE_PRO_PRICE_ID!,
  enterprise: process.env.STRIPE_ENTERPRISE_PRICE_ID!,
};

Webhook Handler — The Critical Piece

Stripe webhooks keep your database in sync with billing state. Miss these and customers lose access even though they paid.

import { Webhook } from 'svix'; // or stripe's own webhook verification

export async function POST(req: Request) {
  const body = await req.text();
  const sig = req.headers.get('stripe-signature')!;

  let event: Stripe.Event;
  try {
    event = stripe.webhooks.constructEvent(
      body,
      sig,
      process.env.STRIPE_WEBHOOK_SECRET!
    );
  } catch {
    return new Response('Invalid signature', { status: 400 });
  }

  switch (event.type) {
    case 'customer.subscription.updated':
    case 'customer.subscription.deleted': {
      const sub = event.data.object as Stripe.Subscription;
      await db.tenant.update({
        where: { stripeSubscriptionId: sub.id },
        data: {
          status: sub.status === 'active' ? 'active' : 'suspended',
          plan: getPlanFromPriceId(sub.items.data[0].price.id),
          currentPeriodEnd: new Date(sub.current_period_end * 1000),
        },
      });
      break;
    }

    case 'invoice.payment_failed': {
      const invoice = event.data.object as Stripe.Invoice;
      // Grace period: don't immediately suspend
      await scheduleGracePeriodCheck(invoice.customer as string);
      break;
    }

    case 'invoice.payment_succeeded': {
      const invoice = event.data.object as Stripe.Invoice;
      await db.tenant.update({
        where: { stripeCustomerId: invoice.customer as string },
        data: { status: 'active', suspendedAt: null },
      });
      break;
    }
  }

  return new Response('OK');
}

Feature Gating

// middleware/tenant.ts
export async function getTenantFromRequest(req: Request) {
  const session = await getSession(req);
  const tenant = await db.tenant.findUnique({
    where: { id: session.tenantId },
  });

  if (!tenant || tenant.status !== 'active') {
    throw new Error('Tenant suspended or not found');
  }

  return tenant;
}

// Feature flags per plan
const PLAN_FEATURES = {
  starter: { apiCalls: 1000, seats: 3, customDomain: false },
  pro: { apiCalls: 50000, seats: 15, customDomain: true },
  enterprise: { apiCalls: Infinity, seats: Infinity, customDomain: true },
} as const;

export function canUsFeature(
  tenant: Tenant,
  feature: keyof typeof PLAN_FEATURES.starter
) {
  return PLAN_FEATURES[tenant.plan][feature];
}

The Migration Problem

Migrating RLS tables is painful. Every ALTER TABLE requires updating policies. My approach:

1. Never run migrations directly in production — always use a migration tool (Prisma Migrate, Flyway)
2. Test migrations with realistic tenant data (use COPY to snapshot + restore)
3. Index tenant_id on every table — RLS does a seq scan otherwise

-- Critical: index for RLS performance
CREATE INDEX CONCURRENTLY idx_users_tenant_id ON users(tenant_id);
CREATE INDEX CONCURRENTLY idx_orders_tenant_id ON orders(tenant_id);

What I'd Do Differently

Building the AI SaaS Starter Kit taught me three things:

1. Add tenant_id to every table from day one — retrofitting RLS to existing tables is a week of pain
2. Test tenant isolation with integration tests — unit tests miss cross-tenant leaks
3. Stripe webhooks need idempotency — the same event can arrive twice; use event.id as an idempotency key

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This architecture powers whoffagents.com. The AI SaaS Starter Kit includes this exact multi-tenant setup, pre-wired with Stripe, Postgres RLS, and Next.js App Router — ready to deploy in 4 hours.

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