How do you implement a multi-tenant architecture in Node.js?

Question

Accepted Answer

**Multi-tenancy** — serve multiple customers from one application.

```javascript
// Strategy 1: Subdomain-based
app.use((req, res, next) => {
    const host = req.hostname;
    req.tenant = host.split(".")[0]; // "acme" from "acme.example.com"
    next();
});

// Strategy 2: Header-based
app.use((req, res, next) => {
    req.tenant = req.headers["x-tenant-id"];
    next();
});

// Tenant-aware database
class TenantDB {
    constructor() {
        this.pools = new Map();
    }

getPool(tenantId) {
        if (!this.pools.has(tenantId)) {
            this.pools.set(tenantId, new Pool({
                database: `tenant_${tenantId}`,
                ...baseConfig,
            }));
        }
        return this.pools.get(tenantId);
    }
}

// Middleware
app.use((req, res, next) => {
    req.db = tenantDB.getPool(req.tenant);
    next();
});

app.get("/products", async (req, res) => {
    const products = await req.db.query("SELECT * FROM products");
    res.json(products);
});
```

**Strategies:**
- Separate databases per tenant.
- Shared database, tenant_id column.
- Shared schema, row-level security.

Node.js: How do you implement a multi-tenant architecture in Node.js?