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

Quickstart (Next.js App Router)

Install the SDK:

bashCopy code
npm install @vercel/queue

Publish from any route, Server Action, or function:

tsCopy code
// 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:

tsCopy code
// 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:

jsonCopy code
{
  "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

tsCopy code
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:

tsCopy code
// 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:

Handle poison messages by acknowledging after a delivery-count threshold:

tsCopy code
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