05 — Architecture and Stack

Default stack: _kernel/standards.md#stack. Override conditions below.

Cloudflare-first decision tree

Compute: Workers (default, every HTTP/cron/queue) · Pages (static-only marketing, rare) · Containers (non-JS runtimes: Playwright headful, ffmpeg, Python ML, build orchestration) · Sandbox SDK (generated/risky code before live promotion)

State: D1 (default relational, ≤10GB/db, Sessions API read-replicas, Time Travel 30-day PIT) · KV (eventually-consistent, cache/sessions/feature-flags) · R2 (object storage, lifecycle Standard→IA after 30d) · Durable Objects (coordination + strongly-consistent SQLite storage since Apr 2025, chat rooms/builder sessions/rate-limiting) · Hyperdrive (front external Postgres/MySQL) · Vectorize (semantic search/RAG, 5M dim/index, topK 100, 10 metadata indexes)

Async: Queues (best-effort, 5000 msg/sec, R2 event notifications) · Workflows v2 (deterministic, 50K concurrent, 300 creates/sec, 2M queued/workflow, step.do + step.sleep + step.waitForEvent) · Inngest (event-driven, better DX/observability)

AI: Workers AI (Llama 4 Scout 17B default — multimodal, free tier; GLM-4.7-flash tool-calling; 3.3 70B legacy) · AI Gateway (caching + rate-limit + fallback + logging for every LLM call) · Vectorize (embeddings + ANN search)

Override conditions (when CF isn't enough)

Need	Fallback	Adapter
Advanced SQL (RLS, OLAP, partial indexes)	Neon Postgres via Hyperdrive	SqlPort
Redis primitives at scale (sorted sets, streams)	Upstash Redis	KvPort
Sub-millisecond global state	Upstash QStash	QueuePort
Specific provider (OpenAI assistants, Anthropic batch)	Direct API via AI Gateway	AiPort
Vector + SQL co-located	Neon pgvector	VectorPort

Adapters live in libs/core/ports/. Product code imports port, never vendor SDK directly. See rules/cloudflare-hostable-supervisor.md.

Auth (default Clerk M2M JWT)

• Clerk — M2M JWT (free, networkless verification), passkeys, OAuth, magic links; Better Auth when Clerk pricing doesn't fit (rare) (free tier: 50K MRU since 2026-02)
• Hash API keys at rest. Audit log every sensitive action.
• Tenant isolation: every table carries org_id, every query filters by it (404 on mismatch, never 403)

Data patterns

D1

[[d1_databases]]
binding = "DB"
database_name = "myapp"

• wrangler types against compatibility_date + bindings (preferred over hand-maintained Env interface)
• Drizzle v1 RQBv2 + Zod for query + validation; batch via db.batch([...]) (no transactions in D1)
• Sessions API: db.withSession(bookmark) · Time Travel: wrangler d1 time-travel restore

R2: per-extension content-type on upload · lifecycle Standard→IA after 30d · event notifications → Queues at 5000 msg/sec for thumbnailing/indexing · versioning for asset rollback

Durable Objects: one DO per stateful entity · SQLite-backed, 10GB per DO · direct stub env.MY_DO.getByName(name) · alarm misfires → idempotent handler

Reliability

• Workers CPU 10ms free / 50ms paid default (configurable 5min); wall time 30s paid
• ctx.waitUntil() for async post-response work; ctx.passThroughOnException() for graceful degradation
• WebSocket + JSRPC payload up to 32 MiB

Cost discipline

• Workers free tier: 100k req/day; Workers Paid: $5/mo (10M req + 30M CPU-ms) + $0.30/M extra req + $0.02/M extra CPU-ms
• D1 free: 5M rows-read + 100K rows-written/day — exceeding either hard-fails every query until 00:00 UTC reset (since 2026-09); 500MB/DB, 5GB account total
• D1 on Workers Paid: 5GB + 25B rows-read + 50M rows-written/mo; then $0.75/GB-mo + $0.001/M rows-read + $1/M rows-written; 10GB/DB hard cap; no egress; read replication included (verified 2026-10-04 against developers.cloudflare.com — Workers/D1/R2 rates all unchanged)
• R2: 10GB free, $0.015/GB-mo, $0/egress · Workers AI Llama 4 Scout FREE · AI Gateway free
• Solo SaaS <$100k/mo MRR stays 10-100× cheaper than AWS-equivalent on CF

Default config (wrangler.jsonc)

{
  "name": "myapp",
  "main": "src/worker/index.ts",
  "compatibility_date": "2026-04-15",
  "compatibility_flags": ["nodejs_compat"],
  "observability": { "enabled": true },
  "secrets_required": ["CLERK_SECRET_KEY", "RESEND_API_KEY"],
  "d1_databases": [{ "binding": "DB", "database_name": "myapp" }],
  "kv_namespaces": [{ "binding": "CACHE", "id": "..." }],
  "r2_buckets": [{ "binding": "BUCKET", "bucket_name": "myapp-assets" }],
  "ai": { "binding": "AI" }
}

Decision template (use for every architecture call)

1. Can CF primitive do this? → Use it.
2. Does this need adapter for portability? → Adapter only if real business case.
3. Cost projection at 10× current scale → Still affordable?
4. Failure mode → Graceful degradation defined?
5. Migration path → If we have to leave CF, what does it cost?

See submodules: cloudflare-primitives.md, data-patterns.md, reliability.md, auth-patterns.md.