# What's the Delay node in Node-RED used for?
The Delay node allows you to introduce a delay in the flow of messages between nodes. It can be useful in various scenarios where you need to control the timing of message processing. For example, the delay node can limit the rate at which messages are processed downstream or throttle the flow of messaging. Both can be useful for interacting with external systems that may have limitations in place.
Here are some other use cases for using the Delay node:
Batch Processing: If you're dealing with a stream of incoming data that you want to process in batches, you can use the Delay node to introduce a delay between groups of messages. This can be helpful when you need to aggregate or analyze data in chunks.
Sequential Processing: Sometimes you need to ensure that messages are processed in a specific order. The Delay node can be used to enforce a sequence of message processing, especially when dealing with asynchronous systems that might not guarantee order.
Simulation and Testing: In testing and simulation scenarios, you might want to mimic real-world timing conditions. The Delay node can help you introduce delays that simulate actual conditions, allowing you to test how your system behaves over time.
Time-based Triggers: You can use the Delay node to trigger actions at specific time intervals. For instance, you might want to send a status update every hour or perform a cleanup task at the end of the day.
Circuit Breaker: The Delay node can be employed as a simple form of circuit breaker. If a downstream system is failing or experiencing issues, you can introduce a delay before retrying, giving the system some time to recover.
# Examples for the Delay node
An example of using the Delay node to rate limit http request to an external API.
Delays each message passing through the node or limits the rate at which they can pass.
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