YepAPI/skills

Multi-Tenancy

Rules

• Row-level isolation (default): add tenantId column to every tenant-scoped table — enforce via middleware or RLS (Row-Level Security)
• Schema-per-tenant: use when tenants need custom schemas or strict data isolation — more complex ops, better isolation
• Subdomain routing: parse tenant from {tenant}.app.com — resolve in middleware, set tenantId on request context
• Custom domains: CNAME to your app, lookup tenant by Host header — use a domains table mapping custom domains to tenant IDs
• Per-tenant config: store theme (logo, colors), feature flags, and limits in a tenant_settings table — cache in memory with TTL
• RLS pattern (Postgres): ALTER TABLE posts ENABLE ROW LEVEL SECURITY; CREATE POLICY tenant_isolation ON posts USING (tenant_id = current_setting('app.tenant_id'))
• Middleware: extract tenant from subdomain/header, set on context, apply to all database queries — never let a query run without tenant scope
• Data partitioning: for large tables, partition by tenantId — improves query performance and enables per-tenant backup/restore

Row-Level Isolation Pattern

// Middleware - extract tenant from subdomain
function getTenantFromHost(host: string): string {
  const subdomain = host.split(".")[0];
  return subdomain; // or lookup in tenants table
}

// Prisma middleware - auto-filter by tenantId
prisma.$use(async (params, next) => {
  if (TENANT_MODELS.includes(params.model)) {
    params.args.where = { ...params.args.where, tenantId: context.tenantId };
  }
  return next(params);
});

Subdomain Routing (Next.js Middleware)

export function middleware(request: NextRequest) {
  const host = request.headers.get("host") ?? "";
  const tenant = host.split(".")[0];
  const response = NextResponse.next();
  response.headers.set("x-tenant-id", tenant);
  return response;
}

Avoid

• Queries without tenant scope — one missing WHERE tenantId = ? leaks data across tenants
• Hardcoding tenant in client — resolve from subdomain/domain server-side
• No index on tenantId — every tenant-scoped table needs a composite index starting with tenantId
• Mixing tenant data in shared caches — namespace cache keys with {tenantId}:{key}