Introduce delays in flow execution for rate limiting, timing coordination, and scheduled operations.

delay Block

The delay block delays each message passing through the node or limits the rate at which they can pass.

Overview

When configured to delay messages, the delay interval can be a fixed value, a random value within a range or dynamically set for each message. Each message is delayed independently of any other message, based on the time of its arrival.

When configured to rate limit messages, their delivery is spread across the configured time period. The status shows the number of messages currently in the queue. It can optionally discard intermediate messages as they arrive.

If set to allow override of the rate, the new rate will be applied immediately, and will remain in effect until changed again, the node is reset, or the flow is restarted.

The rate limiting can be applied to all messages, or group them according to their msg.topic value. When grouping, intermediate messages are automatically dropped. At each time interval, the node can either release the most recent message for all topics, or release the most recent message for the next topic.

Note: In rate limit mode the maximum queue depth can be set by a property in your settings.js file. For example nodeMessageBufferMaxLength: 1000,

Delay: Fixed time delay (e.g., 5 seconds, 1 minute)
Units: Seconds, minutes, hours, or milliseconds

Random Delay

Min Delay: Minimum delay time
Max Delay: Maximum delay time
Units: Seconds, minutes, hours, or milliseconds

Rate Limiting

Rate: Number of messages per time period
Time Period: Seconds, minutes, or hours
Burst Size: Maximum number of messages to allow in burst

Queue Management

Queue Size

Max Queue Size: Maximum number of messages to queue
Drop Policy: What to do when queue is full:
- Drop New: Drop new messages when queue is full
- Drop Old: Drop oldest messages when queue is full

Message Handling

Pass Through: Allow messages to pass through without delay
Queue Messages: Queue messages for delayed processing

Common Use Cases

Rate Limiting API Calls

Limit the rate of API requests to avoid hitting rate limits:

{
  "delayType": "rate",
  "rate": 10,
  "timePeriod": "minute",
  "maxQueueSize": 100,
  "dropPolicy": "dropNew"
}

Batch Processing Delays

Add delays between batch processing operations:

{
  "delayType": "fixed",
  "delay": 2,
  "units": "seconds"
}

Random Processing Times

Simulate realistic processing times with random delays:

{
  "delayType": "random",
  "minDelay": 1,
  "maxDelay": 5,
  "units": "seconds"
}

Scheduled Operations

Implement scheduled processing with delays:

{
  "delayType": "fixed",
  "delay": 30,
  "units": "minutes"
}

Throttling High-Volume Data

Throttle high-volume data streams:

{
  "delayType": "rate",
  "rate": 100,
  "timePeriod": "minute",
  "maxQueueSize": 1000,
  "dropPolicy": "dropOld"
}

Advanced Features

Dynamic Delays

Use expressions to calculate delays dynamically:

{
  "delayType": "fixed",
  "delay": "{{msg.payload.priority === 'high' ? 1 : 5}}",
  "units": "seconds"
}

Conditional Delays

Apply delays based on message content:

{
  "delayType": "fixed",
  "delay": "{{msg.payload.retryCount * 2}}",
  "units": "seconds"
}

Queue Monitoring

Monitor queue status and performance:

{
  "delayType": "rate",
  "rate": 50,
  "timePeriod": "minute",
  "maxQueueSize": 500,
  "dropPolicy": "dropNew",
  "monitorQueue": true
}

Tips

Use rate limiting to respect external API rate limits
Implement random delays to avoid thundering herd problems
Set appropriate queue sizes based on your system capacity
Use drop policies to handle overflow gracefully
Monitor queue performance to optimize delay settings
Consider using delays for testing and simulation
Use fixed delays for predictable timing requirements

Notes

Delays are applied per message, not per flow
Queue size limits help prevent memory issues
Rate limiting is approximate and may vary slightly
Random delays help distribute load more evenly
The block preserves message order when possible
Delays are measured from when the message arrives at the block

trigger - For advanced timing control
inject - For scheduled message injection
batch - For grouping messages before processing

delay