queues

# Vercel Queues You are an expert in Vercel Queues, the durable message topics that power background work and agent events on Vercel. ## What It Is Vercel Queues (public beta) gives you durable, append-only topics. Producers publish JSON messages, and every subscribed consumer group receives every message with at-least-once delivery and automatic retries. New consumer groups can join later and replay non-expired history. Queues is the primitive under Vercel Workflows; use Queues directly when you need control over publishing, consumption, and routing. - **Topic**: a named durable log of messages, created on first publish - **Consumer group**: an independent subscriber that receives every message on a topic - **Delivery**: at-least-once; handlers must be idempotent - **Retention**: 24 hours by default, up to 7 days; delivery can be delayed up to the retention period - **Modes**: push (Vercel invokes your function) or poll (your own workers pull messages from any environment) ## Choose Queues or Workflows | Need | Use | Why | |------|-----|-----| | Fire-and-forget background job, fan-out, buffering | **Queues** | Direct publish/consume, independent consumer groups | | Multi-step logic with sleep, hooks, or human approval | **Workflows** (`⤳ skill: workflow`) | Durable steps and replay built on top of Queues | | Scheduled invocation on a cron | Cron Jobs (`⤳ skill: vercel-functions`) | Time-based trigger, not message-based | ## Quickstart (Next.js App Router) Install the SDK: ```bash npm install @vercel/queue ``` Publish from any route, Server Action, or function: ```ts // app/api/orders/route.ts import { send } from '@vercel/queue'; export async function POST(request: Request) { const body = await request.json(); const { messageId } = await send('orders', { orderId: body.orderId, action: 'process' }); return Response.json({ messageId }); } ``` Consume with a push-mode handler. Messages are acknowledged when the handler returns and retried when it throws: ```ts // app/api/queues/process-order/route.ts import { handleCallback } from '@vercel/queue'; export const POST = handleCallback(async (message, metadata) => { await processOrder(message); console.log('processed', metadata.messageId, 'delivery', metadata.deliveryCount); }); ``` Register the consumer in `vercel.json` (or `vercel.ts`) so Vercel routes the topic to that function: ```json { "functions": { "app/api/queues/process-order/route.ts": { "experimentalTriggers": [{ "type": "queue/v2beta", "topic": "orders" }] } } } ``` Run `vercel link` and `vercel env pull` before local development so the SDK can authenticate. ## Send Options ```ts await send('orders', payload, { region: 'sfo1', // target a specific region retentionSeconds: 3600, // message TTL; min 60, max 604800 (7 days); default 24 hours delaySeconds: 60, // delay first delivery; max 7 days, capped at the TTL idempotencyKey: 'order-123', // duplicates within the retention window are dropped headers: { 'x-trace-id': 'abc-123' }, }); ``` Create a `QueueClient` when you need defaults, a fixed region, or multiple clients: ```ts // lib/queue.ts import { QueueClient } from '@vercel/queue'; const queue = new QueueClient({ region: 'sfo1' }); export const { send, handleCallback } = queue; ``` ## Consumer Options and Retries `handleCallback(handler, options)` accepts: | Option | Default | Notes | |--------|---------|-------| | `visibilityTimeoutSeconds` | 300 | How long a message stays in flight; the SDK re-extends the lease while the handler runs | | `retry` | built-in backoff | `(error, metadata) => { afterSeconds } \| { acknowledge: true } \| undefined` | Handle poison messages by acknowledging after a delivery-count threshold: ```ts export const POST = handleCallback(processOrder, { retry: (error, metadata) => { if (metadata.deliveryCount > 5) return { acknowledge: true }; // stop retrying return { afterSeconds: Math.min(300, 2 ** metadata.deliveryCount * 5) }; }, }); ``` `metadata` includes `messageId`, `deliveryCount`, `createdAt`, `expiresAt`, `topicName`, `consumerGroup`, and `region`. For Express, Connect, or Next.js Pages Router handlers use `queue.handleNodeCallback(async (message, metadata) => ...)` from a `QueueClient` instance, which takes `(req, res)`. ## Other Runtimes and Frameworks - **Python**: `vercel-queue` publishes and consumes with the same topic model, and FastAPI, Flask, and Django apps can use it; Celery and Dramatiq integrations are documented under the Python backend frameworks. - **Nitro / Nuxt**: declare `vercel.queues.triggers` in `nitro.config.ts` and handle messages with the `vercel:queue` runtime hook; `send` from `@vercel/queue` works in any server route. - **Poll mode**: pull messages from your own workers in any environment when push delivery to a Vercel Function does not fit. - **Payloads**: JSON by default; use `BufferTransport` for binary or `StreamTransport` for large bodies when constructing a `QueueClient`. ## Errors `@vercel/queue` exports typed errors: `UnauthorizedError`, `BadRequestError`, `DuplicateMessageError` (idempotency-key collision), `MessageNotFoundError`, and `QueueEmptyError`. ## Common Pitfalls 1. **Missing trigger**: a `handleCallback` route with no `experimentalTriggers` entry never receives messages. Register every consumer in `vercel.json`/`vercel.ts`. 2. **Non-idempotent handlers**: delivery is at-least-once. Key side effects on `metadata.messageId` or your own `idempotencyKey`. 3. **Retrying forever**: without a `retry` policy that acknowledges poison messages, a permanently failing message is redelivered until it expires. 4. **Using Queues for multi-step logic**: if you need sleep, hooks, or approvals between steps, use Workflows instead of chaining topics by hand. 5. **Local dev without credentials**: run `vercel link` and `vercel env pull` first; otherwise `send()` fails with `UnauthorizedError`. ## References - 📖 docs: https://vercel.com/docs/queues - 📖 JS SDK: https://vercel.com/docs/queues/sdk - 📖 Python SDK: https://vercel.com/docs/queues/python-sdk - 📖 poll mode: https://vercel.com/docs/queues/poll-mode - 📖 pricing and limits: https://vercel.com/docs/queues/pricing