Cloudflare Queues

Producer API

// 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' } },
]);

Critical Limits:

• Message size: 128 KB max (including ~100 bytes metadata)
• Messages >128 KB will fail - store in R2 and send reference instead
• Batch size: 100 messages or 256 KB total
• Delay: 0-43200 seconds (12 hours max)

HTTP Publishing (May 2025+)

New in May 2025: Publish messages to queues via HTTP from any service or programming language.

Source: Cloudflare Changelog

Authentication: Requires Cloudflare API token with Queues Edit permissions.

# Single message
curl -X POST "https://api.cloudflare.com/client/v4/accounts/{account_id}/queues/my-queue/messages" \
  -H "Authorization: Bearer YOUR_API_TOKEN" \
  -H "Content-Type: application/json" \
  -d '{
    "messages": [
      {"body": {"userId": "123", "action": "process-order"}}
    ]
  }'

# Batch messages
curl -X POST "https://api.cloudflare.com/client/v4/accounts/{account_id}/queues/my-queue/messages" \
  -H "Authorization: Bearer YOUR_API_TOKEN" \
  -H "Content-Type: application/json" \
  -d '{
    "messages": [
      {"body": {"userId": "1"}},
      {"body": {"userId": "2"}},
      {"body": {"userId": "3"}}
    ]
  }'

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

Event Subscriptions (August 2025+)

New in August 2025: Subscribe to events from Cloudflare services and consume via Queues.

Source: Cloudflare Changelog

Supported Event Sources:

• R2 (bucket.created, object.uploaded, object.deleted, etc.)
• Workers KV
• Workers AI
• Vectorize
• Workflows
• Super Slurper
• Workers Builds

Create Subscription:

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

Event Structure:

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;
  };
}

Consumer Example:

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();
    }
  }
};

Use Cases:

• Build custom workflows triggered by R2 uploads
• Monitor infrastructure changes (new KV namespaces, buckets)
• Track AI inference jobs
• Audit account activity
• Event-driven architectures without custom webhooks

Consumer API

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

Critical:

• message.ack() - Mark success, prevents retry even if handler fails later
• Use explicit ack for non-idempotent operations (DB writes, API calls, payments)
• Implicit ack - If handler returns successfully without calling ack(), all messages auto-acknowledged
• Ordering not guaranteed - Don't assume FIFO message order

Critical Consumer Patterns

Explicit Acknowledgement (Non-Idempotent Operations)

ALWAYS use explicit ack() for: Database writes, API calls, financial transactions

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
      }
    }
  }
};

Why? Prevents duplicate writes if one message in batch fails. Failed messages retry independently.

Exponential Backoff for Rate-Limited APIs

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();
        }
      }
    }
  }
};

Dead Letter Queue (DLQ) - CRITICAL for Production

⚠️ Without DLQ, failed messages are DELETED PERMANENTLY after max_retries

npx wrangler queues create my-dlq

wrangler.jsonc:

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

DLQ Consumer:

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
    }
  }
};

Known Issues Prevention

This skill prevents 13 documented issues:

Issue #1: Multiple Dev Commands - Queues Don't Flow Between Processes

Error: Queue messages sent in one wrangler dev process don't appear in another wrangler dev consumer process Source: GitHub Issue #9795

Why It Happens: The virtual queue used by wrangler is in-process memory. Separate dev processes cannot share the queue state.

Prevention:

# ❌ Don't run producer and consumer as separate processes
# Terminal 1: wrangler dev (producer)
# Terminal 2: wrangler dev (consumer)  # Won't receive messages!

# ✅ Option 1: Run both in single dev command
wrangler dev -c producer/wrangler.jsonc -c consumer/wrangler.jsonc

# ✅ Option 2: Use Vite plugin with auxiliaryWorkers
# vite.config.ts:
export default defineConfig({
  plugins: [
    cloudflare({
      auxiliaryWorkers: ['./consumer/wrangler.jsonc']
    })
  ]
})

Issue #2: Queue Producer Binding Causes 500 Errors with Remote Dev

Error: All routes return 500 Internal Server Error when using wrangler dev --remote with queue bindings Source: GitHub Issue #9642

Why It Happens: Queues are not yet supported in wrangler dev --remote mode. Even routes that don't use the queue binding fail.

Prevention:

// 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)

Issue #3: D1 Remote Breaks When Queue Remote is Set

Error: D1 remote binding stops working when remote: true is set on queue producer binding Source: GitHub Issue #11106

Why It Happens: Binding conflict issue affecting mixed local/remote development.

Prevention:

// ❌ 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" }]
  }
}

Status: No workaround yet. Track issue for updates.

Issue #4: Mixed Local/Remote Bindings - Queue Consumer Missing

Error: Queue consumer binding does not appear when mixing local queues with remote AI/Vectorize bindings Source: GitHub Issue #9887

Why It Happens: Wrangler doesn't support mixed local/remote bindings in the same worker.

Prevention:

// ❌ 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)

Issue #5: http_pull Type Prevents Worker Consumer Execution

Error: Queue consumer with type: "http_pull" doesn't execute in production Source: GitHub Issue #6619

Why It Happens: http_pull is for external HTTP-based consumers, not Worker-based consumers.

Prevention:

// ❌ 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
    }]
  }
}

Breaking Changes & Deprecations

delivery_delay in Producer Config (Upcoming Removal)

Warning: The delivery_delay parameter in producer bindings will be removed in a future wrangler version.

Source: GitHub Issue #10286

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

Migration: Use per-message delay instead:

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

Why: Workers should not affect queue-level settings. With multiple producers, the setting from the last-deployed producer wins, causing unpredictable behavior.

Community Tips

Note: These tips come from community discussions and GitHub issues. Verify against your wrangler version.

Tip: max_batch_timeout May Break Local Development

Source: GitHub Issue #6619 Confidence: MEDIUM Applies to: Local development with wrangler dev

If your queue consumer doesn't execute locally, try removing max_batch_timeout:

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

This appears to be version-specific and may not affect all setups.

Tip: Queue Name Not Available on Producer Bindings

Source: GitHub Issue #10131 Confidence: HIGH Applies to: Multi-environment deployments (staging, PR previews, tenant-specific queues)

Queue names are only available via batch.queue in consumer handlers, not on producer bindings. This creates issues with environment-specific queue names like email-queue-staging or email-queue-pr-123.

Current Limitation:

// ❌ 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
}

Workaround:

// 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
}

Status: Feature request tracked internally: MQ-923

Consumer Configuration

{
  "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
    }]
  }
}

Critical Settings:

• Batching - Consumer called when EITHER condition met (max_batch_size OR max_batch_timeout)
• max_retries - After exhausted: with DLQ → sent to DLQ, without DLQ → DELETED PERMANENTLY
• max_concurrency - Only set if upstream has rate limits or connection limits. Otherwise leave unset for auto-scaling (up to 250 concurrent invocations)
• DLQ - Create separately: npx wrangler queues create my-dlq

Wrangler Commands

# Create queue
npx wrangler queues create my-queue
npx wrangler queues create my-queue --message-retention-period-secs 1209600  # 14 days

# Manage queues
npx wrangler queues list
npx wrangler queues info my-queue
npx wrangler queues delete my-queue  # ⚠️ Deletes ALL messages!

# Pause/Purge (March 2025 - NEW)
npx wrangler queues pause-delivery my-queue   # Pause processing, keep receiving
npx wrangler queues resume-delivery my-queue
npx wrangler queues purge my-queue            # ⚠️ Permanently deletes all messages!

# Consumer management
npx wrangler queues consumer add my-queue my-consumer-worker \
  --batch-size 50 --batch-timeout 10 --message-retries 5
npx wrangler queues consumer remove my-queue my-consumer-worker

Limits & Quotas

Pricing

Requires Workers Paid plan ($5/month)

Operations Pricing:

• First 1,000,000 operations/month: FREE
• After that: $0.40 per million operations

What counts as an operation:

• Each 64 KB chunk written, read, or deleted
• Messages >64 KB count as multiple operations:
  • 65 KB message = 2 operations
  • 127 KB message = 2 operations
  • 128 KB message = 2 operations

Typical message lifecycle:

• 1 write + 1 read + 1 delete = 3 operations

Retries:

• Each retry = additional read operation
• Message retried 3 times = 1 write + 4 reads + 1 delete = 6 operations

Dead Letter Queue:

• Writing to DLQ = additional write operation

Cost examples:

• 1M messages/month (no retries): ((1M × 3) - 1M) / 1M × $0.40 = $0.80
• 10M messages/month: ((10M × 3) - 1M) / 1M × $0.40 = $11.60
• 100M messages/month: ((100M × 3) - 1M) / 1M × $0.40 = $119.60

Error Handling

Common Errors

1. Message Too Large

// ❌ 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);
}

2. Throughput Exceeded

// ❌ 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
  }
}

3. Consumer Timeout

// ❌ 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

wrangler.jsonc:

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

4. Backlog Growing

// 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();
      })
    );
  },
};

Critical Rules

Always:

• ✅ Configure DLQ for production (dead_letter_queue in consumer config)
• ✅ Use explicit message.ack() for non-idempotent ops (DB writes, API calls)
• ✅ Validate message size <128 KB before sending
• ✅ Use sendBatch() for multiple messages (more efficient)
• ✅ Implement exponential backoff: 60 * Math.pow(2, message.attempts - 1)
• ✅ Let concurrency auto-scale (don't set max_concurrency unless upstream has rate limits)

Never:

• ❌ Never assume FIFO ordering - not guaranteed
• ❌ Never rely on implicit ack for non-idempotent ops - use explicit ack()
• ❌ Never send messages >128 KB - will fail (store in R2 instead)
• ❌ Never skip DLQ in production - failed messages DELETED PERMANENTLY without DLQ
• ❌ Never exceed 5,000 msg/s per queue (push consumers) or rate limits apply
• ❌ Never process messages synchronously - use Promise.all() for parallelism

Troubleshooting

Issue: Messages not being delivered to consumer

Possible causes:

1. Consumer not deployed
2. Wrong queue name in wrangler.jsonc
3. Delivery paused
4. Consumer throwing errors

Solution:

# Check queue info
npx wrangler queues info my-queue

# Check if delivery paused
npx wrangler queues resume-delivery my-queue

# Check consumer logs
npx wrangler tail my-consumer

Issue: Entire batch retried when one message fails

Cause: Using implicit acknowledgement with non-idempotent operations

Solution: Use explicit ack()

// ✅ 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
  }
}

Issue: Messages deleted without processing

Cause: No Dead Letter Queue configured

Solution:

# Create DLQ
npx wrangler queues create my-dlq

# Add to consumer config

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

Issue: Consumer not auto-scaling

Possible causes:

1. max_concurrency set to 1
2. Consumer returning errors (not processing)
3. Batch processing too fast (no backlog)

Solution:

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

Related Documentation

• Cloudflare Queues Docs
• How Queues Works
• JavaScript APIs
• Batching & Retries
• Consumer Concurrency
• Dead Letter Queues
• Wrangler Commands
• Limits
• Pricing

Last Updated: 2026-01-21 Version: 2.0.0 Changes: Added HTTP Publishing (May 2025), Event Subscriptions (Aug 2025), Known Issues Prevention (13 issues), Breaking Changes section, Community Tips. Error count: 0 → 13. Major feature additions and comprehensive issue documentation. Maintainer: Jeremy Dawes | [email protected]