Designs tenant isolation, hostname routing, custom-domain lifecycle, and plan limits on Cloudflare or Vercel. Use when asked to "isolate tenant data", "support custom domains", "build a white-label platform", or assess PSL registration. For general module structure use codebase-architecture; for SEO

Multi Tenant Platform Architecture (Cloudflare or Vercel) IS: platform choice, domain strategy and PSL, tenant identification, compute and data isolation, hostname routing, tenant context propagation, custom domains and SSL, per tenant static files, and mapping platform limits to plans. IS NOT: general folder structure or module contracts (use codebase architecture ), scaffolding a new repo (use scaffold nextjs ), or the content of per tenant SEO files once routing serves them dynamically: sitemap entries, canonical URLs, structured data, indexing policy (use seo ). Contents Platform dispatch (decide first) Reference files Workflow (order matters) Gotchas Output schema Pre commit checklist Related skills Platform dispatch (decide first) Signals Platform Model Tenants upload or generate their own code; code level isolation; edge compute on KV, D1, Durable Objects, R2 Cloudflare Dispatch Worker in front of a dispatch namespace of per tenant Workers; Cloudflare for SaaS for custom hostnames Every tenant runs the same Next.js codebase and differs by content, branding, and plan; ISR, Server Components, Vercel deploys Vercel One deployment; proxy.ts resolves the tenant from the hostname; wildcard plus custom domains on the project Pick one platform per product. Fronting a Vercel app with a Cloudflare proxy doubles the TLS and redirect layers and is the usual cause of redirect loops and failed certificate issuance. Tenants shipping their own code on Vercel is the multi project model (one Vercel project per tenant, created with the SDK). It follows the Cloudflare row's isolation reasoning; this skill's Vercel references cover the single deployment model only. Reference files File Read when [cloudflare platform.md](references/cloudflare platform.md) Cloudflare chosen: dispatch namespaces, routing, Cloudflare for SaaS custom hostnames, isolation modes, KV and D1 (steps 3 to 7) [vercel platform.md](references/vercel platform.md) Vercel chosen: proxy.ts resolution, App Router layout, Global Config lookups, per tenant static files, custom subpaths, local dev (steps 4 to 7) [vercel domains.md](references/vercel domains.md) Vercel chosen: SDK domain lifecycle, DNS targets, verification, wildcard nameservers, SSL, troubleshooting (step 7) [data isolation.md](references/data isolation.md) Step 3 on either platform: shared schema with RLS, schema per tenant, database per tenant, and the Postgres/Supabase/Drizzle policy pattern [psl.md](references/psl.md) Step 1 when tenants publish content or run code on sibling subdomains: eligibility, submission, interim cookie controls [limits and quotas.md](references/limits and quotas.md) Step 8: dated snapshot of Cloudflare, Vercel, and Neon limits to map onto plans agents/openai.yaml Never during a task: launcher metadata for external runners Workflow (order matters) Copy this checklist to track progress: 1. Choose the domain strategy Put tenant workloads on a dedicated registrable domain ( acme.app for tenants, acme.com for brand). One phishing tenant on x.acme.com puts the whole domain on blocklists, and a tenant cookie with Domain=acme.com reaches your dashboard. Keep the dashboard and auth on a different apex from tenant subdomains ( app.acme.com for the console, .acme.app for tenants). If tenants publish content or run code on sibling subdomains, submit the label directly above the tenant name ( acme.app , or sites.acme.app for <tenant .sites.acme.app ) to the PSL and start now: there is no SLA. Tenant owned custom domains need no PSL entry. Otherwise record No PSL with the reason. 2. Choose tenant identification (one primary; custom domain as the upgrade path) Subdomain tenant.acme.app : wildcard DNS plus wildcard certificate. The default. Custom domain tenant.com : the tenant CNAMEs to you. Paying tenants; reputation shifts to them; needs the onboarding lifecycle in step 7. Path acme.app/tenant : no per tenant DNS or certificates, but no cookie isolation and no branding. Choose it only when tenants will never get a hostname. 3. Define the isolation model Compute, Cloudflare: one dispatch namespace in untrusted mode; per invocation cpuMs and subRequests limits per plan; an outbound Worker if tenant code may call the internet. Compute, Vercel: one deployment, tenant code never executes. If tenants must ship code, move to Vercel multi project or Cloudflare rather than sandboxing inside the app. Data: shared schema with tenant id on every tenant aware table plus RLS is the default; database per tenant for regulated or noisy tenants, selectable per plan. See [data isolation.md](references/data isolation.md). 4. Route deterministically (tenants never influence routing or see each other) Cloudflare: a single / route on the SaaS zone to the dispatch Worker; hostname tenant record (KV, D1 on miss) env.DISPATCHER.get(script) ; Worker not found 404. Vercel: proxy.ts (Next.js 16; middleware.ts with runtime: 'nodejs' on 15) reads host , looks the tenant up in Global Config or the database, rewrites into the tenant segment; unknown hostname 404, never the brand site. Let /.well known through before any tenant rewrite. Route robots.txt , sitemap.xml , and llms.txt into the tenant segment so they vary per tenant. 5. Propagate tenant context from one authority Delete every inbound x tenant header, set x tenant id , x tenant slug , x tenant plan from the resolved tenant, and forward them on the request ( NextResponse.next({ request: { headers } }) ). Server Components read await headers() ; route handlers read request.headers . Cloudflare: the dispatch Worker sets headers or passes parameters before fetch . The proxy is routing, not authorization. Server Functions, route handlers, and jobs re derive the tenant from the session and the data layer enforces it (RLS or tenant id predicates). 6. Bind only what the tenant needs Cloudflare: each user Worker gets its own bindings (KV namespace, D1 database, R2 prefix); adding a binding is an explicit redeploy. No shared globals. Vercel: Global Config holds only hostname { id, slug, plan } ; the database is the source of truth and write through happens when a domain verifies. Feature flags and branding come from the database keyed by tenant id. 7. Support custom domains and per tenant static files Lifecycle to design and record: add domain show DNS target verify ownership certificate issued mapping activated removal or failure path. Cloudflare: Cloudflare for SaaS custom hostname on the SaaS zone, proxied fallback origin, customers.<you .com CNAME target, http or txt validation, pre validate before DNS cutover. See [cloudflare platform.md](references/cloudflare platform.md). Vercel: projectsAddProjectDomain DNS values from the project's domain card vercel TXT only if the domain is already on Vercel projectsVerifyProjectDomain Let's Encrypt HTTP 01. See [vercel domains.md](references/vercel domains.md). robots.txt , sitemap.xml , llms.txt are route handlers inside the tenant segment with explicit Content Type ; nothing tenant specific lives in /public . Their content is seo territory. 8. Surface limits as plans and capture evidence Fill the limits to plan table from [limits and quotas.md](references/limits and quotas.md), re checking each source URL and dating it; enforce at the routing layer (Cloudflare limits , Vercel plan header plus server checks). Nothing long running in the request path: Cloudflare Queues or Workflows, Vercel background functions or cron. Every tenant operation (create tenant, add domain, verify, remove) works over HTTP with the same authority as the UI; if it only works in the dashboard, the platform leaks into the UI. Run the evidence commands in the pre commit checklist and paste results into the output. Gotchas Tenant headers set on the response instead of the request: NextResponse.next({ headers }) sends x tenant id to the browser and headers() in Server Components reads nothing. Use NextResponse.next({ request: { headers: requestHeaders } }) . Forwarding inbound tenant headers: curl H "x tenant id: <other " then serves another tenant's data. Delete or overwrite x tenant on every path through the proxy, including paths that skip resolution. The starter kit matcher '/((?!api next [\\w ]+\\.\\w+). )' excludes every root file with an extension, so robots.txt and sitemap.xml skip the proxy and every tenant gets the platform's /public copy. Match them, and rewrite them into the tenant segment. Next.js 16 renamed middleware.ts to proxy.ts (export proxy , Node.js runtime, a runtime config option throws). npx @next/codemod@canary middleware to proxy . migrates. A matcher that excludes a path also skips Server Function POSTs on it, so tenant checks live in the data layer too. Global Config (formerly Edge Config) key names must match ^[\w ]+$ ; tenant acme.com is rejected. Use a collision free encoding or hash; replacing dots with underscores can map different hostnames to the same key. Writes propagate in up to 10 s, so a "domain connected" screen that reads Global Config right after the write shows stale state; read the database there. The legacy @vercel/edge config SDK cannot read stores connected after the rename (they create GLOBAL CONFIG , not EDGE CONFIG ). RLS is bypassed by superusers and BYPASSRLS roles; table owners bypass it unless FORCE ROW LEVEL SECURITY is enabled. An app connecting as the migration role sees every tenant with policies "on". Connect as a separate role, add ALTER TABLE ... FORCE ROW LEVEL SECURITY , and test with SET ROLE app user . SET app.tenant id = ... outside a transaction on a pooled connection persists into the next request. Use set config('app.tenant id', $1, true) inside the transaction; with PgBouncer in transaction mode it is the only safe form. Wildcard .acme.app on Vercel without Vercel nameservers never gets a certificate: DNS 01 needs Vercel to write acme challenge . Point ns1.vercel dns.com and ns2.vercel dns.com first and re add MX records. /.well known is reserved on Vercel and cannot be rewritten or redirected; a proxy that rewrites every path into /s/[slug] breaks HTTP 01 and custom domain certificates never issue. Pass it through first. Cloudflare for SaaS: the fallback origin must be a proxied record in the SaaS zone; a custom hostname equal to the zone name is unsupported; cf custom hostname pre validation does not work when the customer's zone is also on Cloudflare (O2O, marked by cf connecting o2o: 1 ). Untrusted dispatch namespaces (default) have no request.cf and no caches.default , so tenant code reading request.cf.country throws. Trusted mode restores them but shares one cache across every tenant Worker in the namespace. KV is eventually consistent (up to 60 s, negative lookups cached): a hostname added after the dispatch Worker's first lookup 404s for a minute. Fall back to D1 on miss during onboarding. PSL rejects domains with under two years of registration left; the psl.<suffix TXT stays in place after merge; browsers ship the list on their own release cycles. Listing also kills Domain=acme.app cookies, including your own cross subdomain SSO if it lives there. Starting path based with custom domains on the roadmap means URL rewrites, cookie changes, and DNS migration later. Domain quotas and charges vary by provider and plan. Put current official limits and their access dates in the plan table before setting pricing. Output schema Length follows the decisions: drop any section the project does not face rather than filling it. Pre commit checklist [ ] Platform chosen with rationale; multi project or Cloudflare ch

multi-tenant-architecture