undefined

---

// Send single message
await env.MY_QUEUE.send({ userId: '123', action: 'send-email' });

// Send with delay (max 12 hours)
await env.MY_QUEUE.send({ action: 'reminder' }, { delaySeconds: 600 });

// Send batch (max 100 messages or 256 KB)
await env.MY_QUEUE.sendBatch([
  { body: { userId: '1' } },
  { body: { userId: '2' } },
]);

undefined

**Use Cases**:
- Publishing from external microservices (Node.js, Python, Go, etc.)
- Cron jobs running outside Cloudflare
- Webhook receivers
- Legacy systems integration
- Services without Cloudflare Workers SDK

---

npx wrangler queues subscription create my-queue \
  --source r2 \
  --events bucket.created,object.uploaded

interface CloudflareEvent {
  type: string;           // 'r2.bucket.created', 'kv.namespace.created'
  source: string;         // 'r2', 'kv', 'ai', etc.
  payload: any;           // Event-specific data
  metadata: {
    accountId: string;
    timestamp: string;
  };
}

export default {
  async queue(batch: MessageBatch, env: Env): Promise<void> {
    for (const message of batch.messages) {
      const event = message.body as CloudflareEvent;

      switch (event.type) {
        case 'r2.bucket.created':
          console.log('New R2 bucket:', event.payload.bucketName);
          await notifyAdmin(event.payload);
          break;

        case 'r2.object.uploaded':
          console.log('File uploaded:', event.payload.key);
          await processNewFile(event.payload.key);
          break;

        case 'kv.namespace.created':
          console.log('New KV namespace:', event.payload.namespaceId);
          break;

        case 'ai.inference.completed':
          console.log('AI inference done:', event.payload.modelId);
          break;
      }

      message.ack();
    }
  }
};

export default {
  async queue(batch: MessageBatch, env: Env, ctx: ExecutionContext): Promise<void> {
    for (const message of batch.messages) {
      // message.id - unique UUID
      // message.timestamp - Date when sent
      // message.body - your content
      // message.attempts - retry count (starts at 1)

      await processMessage(message.body);
      message.ack(); // Explicit ack (critical for non-idempotent ops)
    }
  }
};

// Retry with exponential backoff
message.retry({ delaySeconds: Math.min(60 * Math.pow(2, message.attempts - 1), 3600) });

// Batch methods
batch.ackAll();   // Ack all messages
batch.retryAll(); // Retry all messages

export default {
  async queue(batch: MessageBatch, env: Env): Promise<void> {
    for (const message of batch.messages) {
      try {
        await env.DB.prepare('INSERT INTO orders (id, amount) VALUES (?, ?)')
          .bind(message.body.orderId, message.body.amount).run();
        message.ack(); // Only ack on success
      } catch (error) {
        console.error(`Failed ${message.id}:`, error);
        // Don't ack - will retry
      }
    }
  }
};

export default {
  async queue(batch: MessageBatch, env: Env): Promise<void> {
    for (const message of batch.messages) {
      try {
        await fetch('https://api.example.com/process', {
          method: 'POST',
          body: JSON.stringify(message.body),
        });
        message.ack();
      } catch (error) {
        if (error.status === 429) {
          const delaySeconds = Math.min(60 * Math.pow(2, message.attempts - 1), 3600);
          message.retry({ delaySeconds });
        } else {
          message.retry();
        }
      }
    }
  }
};

npx wrangler queues create my-dlq

{
  "queues": {
    "consumers": [{
      "queue": "my-queue",
      "max_retries": 3,
      "dead_letter_queue": "my-dlq"  // Messages go here after 3 failed retries
    }]
  }
}

export default {
  async queue(batch: MessageBatch, env: Env): Promise<void> {
    for (const message of batch.messages) {
      console.error('PERMANENTLY FAILED:', message.id, message.body);
      await env.DB.prepare('INSERT INTO failed_messages (id, body) VALUES (?, ?)')
        .bind(message.id, JSON.stringify(message.body)).run();
      message.ack(); // Remove from DLQ
    }
  }
};

undefined

---

// When using remote dev, temporarily comment out queue bindings
{
  "queues": {
    // "producers": [{ "queue": "my-queue", "binding": "MY_QUEUE" }]
  }
}

// Or use local dev instead
// wrangler dev (without --remote)

// ❌ Don't mix D1 remote with queue remote
{
  "d1_databases": [{
    "binding": "DB",
    "database_id": "...",
    "remote": true
  }],
  "queues": {
    "producers": [{
      "binding": "QUEUE",
      "queue": "my-queue",
      "remote": true  // ❌ Breaks D1 remote
    }]
  }
}

// ✅ Avoid remote on queues when using D1 remote
{
  "d1_databases": [{ "binding": "DB", "remote": true }],
  "queues": {
    "producers": [{ "binding": "QUEUE", "queue": "my-queue" }]
  }
}

// ❌ Don't mix local queues with remote AI
{
  "queues": {
    "consumers": [{ "queue": "my-queue" }]
  },
  "ai": {
    "binding": "AI",
    "experimental_remote": true  // ❌ Breaks queue consumer
  }
}

// ✅ Option 1: All local (no remote bindings)
wrangler dev

// ✅ Option 2: Separate workers for queues vs AI
// Worker 1: Queue processing (local)
// Worker 2: AI operations (remote)

// ❌ Don't use type: "http_pull" for Worker consumers
{
  "queues": {
    "consumers": [{
      "queue": "my-queue",
      "type": "http_pull",  // ❌ Wrong for Workers
      "max_batch_size": 10
    }]
  }
}

// ✅ Omit type field for push-based Worker consumers
{
  "queues": {
    "consumers": [{
      "queue": "my-queue",
      "max_batch_size": 10
      // No "type" field - defaults to Worker consumer
    }]
  }
}

// ❌ Will be removed - don't use
{
  "queues": {
    "producers": [{
      "binding": "MY_QUEUE",
      "queue": "my-queue",
      "delivery_delay": 300  // ❌ Don't use this
    }]
  }
}

// ✅ Correct approach - per-message delay
await env.MY_QUEUE.send({ data }, { delaySeconds: 300 });

{
  "queues": {
    "consumers": [{
      "queue": "my-queue",
      "max_batch_size": 10
      // Remove max_batch_timeout for local dev
    }]
  }
}

// ❌ Can't access queue name from producer binding
const queueName = env.MY_QUEUE.name; // Doesn't exist!

// ❌ Must hardcode or normalize in consumer
switch (batch.queue) {
  case 'email-queue':           // What about email-queue-staging?
  case 'email-queue-staging':   // Must handle all variants
  case 'email-queue-pr-123':    // Dynamic env names break this
}

// In consumer: Normalize queue name
function normalizeQueueName(queueName: string): string {
  return queueName.replace(/-staging|-pr-\d+|-dev/g, '');
}

switch (normalizeQueueName(batch.queue)) {
  case 'email-queue':
    // Handle all email-queue-* variants
}

{
  "queues": {
    "consumers": [{
      "queue": "my-queue",
      "max_batch_size": 100,           // 1-100 (default: 10)
      "max_batch_timeout": 30,         // 0-60s (default: 5s)
      "max_retries": 5,                // 0-100 (default: 3)
      "retry_delay": 300,              // Seconds (default: 0)
      "max_concurrency": 10,           // 1-250 (default: auto-scale)
      "dead_letter_queue": "my-dlq"    // REQUIRED for production
    }]
  }
}

undefined

---

// ❌ Bad: Message >128 KB
await env.MY_QUEUE.send({
  data: largeArray, // >128 KB
});

// ✅ Good: Check size before sending
const message = { data: largeArray };
const size = new TextEncoder().encode(JSON.stringify(message)).length;

if (size > 128000) {
  // Store in R2, send reference
  const key = `messages/${crypto.randomUUID()}.json`;
  await env.MY_BUCKET.put(key, JSON.stringify(message));
  await env.MY_QUEUE.send({ type: 'large-message', r2Key: key });
} else {
  await env.MY_QUEUE.send(message);
}

// ❌ Bad: Exceeding 5000 msg/s per queue
for (let i = 0; i < 10000; i++) {
  await env.MY_QUEUE.send({ id: i }); // Too fast!
}

// ✅ Good: Use sendBatch
const messages = Array.from({ length: 10000 }, (_, i) => ({
  body: { id: i },
}));

// Send in batches of 100
for (let i = 0; i < messages.length; i += 100) {
  await env.MY_QUEUE.sendBatch(messages.slice(i, i + 100));
}

// ✅ Even better: Rate limit with delay
for (let i = 0; i < messages.length; i += 100) {
  await env.MY_QUEUE.sendBatch(messages.slice(i, i + 100));
  if (i + 100 < messages.length) {
    await new Promise(resolve => setTimeout(resolve, 100)); // 100ms delay
  }
}

// ❌ Bad: Long processing without CPU limit increase
export default {
  async queue(batch: MessageBatch): Promise<void> {
    for (const message of batch.messages) {
      await processForMinutes(message.body); // CPU timeout!
    }
  },
};

// ✅ Good: Increase CPU limit in wrangler.jsonc

{
  "limits": {
    "cpu_ms": 300000  // 5 minutes (max allowed)
  }
}

// Issue: Consumer too slow, backlog growing

// ✅ Solution 1: Increase batch size
{
  "queues": {
    "consumers": [{
      "queue": "my-queue",
      "max_batch_size": 100  // Process more per invocation
    }]
  }
}

// ✅ Solution 2: Let concurrency auto-scale (don't set max_concurrency)

// ✅ Solution 3: Optimize consumer code
export default {
  async queue(batch: MessageBatch, env: Env): Promise<void> {
    // Process in parallel
    await Promise.all(
      batch.messages.map(async (message) => {
        await process(message.body);
        message.ack();
      })
    );
  },
};

undefined

---

// ✅ Explicit ack
for (const message of batch.messages) {
  try {
    await dbWrite(message.body);
    message.ack(); // Only ack on success
  } catch (error) {
    console.error(`Failed: ${message.id}`);
    // Don't ack - will retry
  }
}

undefined

```jsonc
{
  "queues": {
    "consumers": [{
      "queue": "my-queue",
      "dead_letter_queue": "my-dlq"
    }]
  }
}

{
  "queues": {
    "consumers": [{
      "queue": "my-queue",
      // Don't set max_concurrency - let it auto-scale
      "max_batch_size": 50  // Increase batch size instead
    }]
  }
}