Rate Limit

Overview

The Rate Limit Traffic Policy action enables you to configure thresholds that restrict the throughput of traffic that successfully reaches your endpoint.

Traffic may be limited overall or by attributes of the incoming requests.

Configuration Reference

This is the Traffic Policy configuration reference for this action.

Action Type

rate-limit

Configuration Fields

Parameter	Type	Description
name	string	Required. A name for this rate limit configuration. Must be less than 1024 characters.
algorithm	string	Required. The rate limit algorithm to be used. Supported options: "sliding_window"
capacity	uint	Required. The maximum number of requests allowed to reach your upstream server. The minimum capacity is 1 and the maximum capacity is 2,000,000,000.
rate	string	Required. The duration in which events may be limited based on the current capacity. This must be specified as a time duration that is a multiple of ten seconds (e.g. "90s", "10m"). The minimum value is "60s" and the maximum value is "24h".
bucket_key	[]string	Required. The elements of this collection define the unique key of a request to collect and track the rate at which the capacity is being met. Possible values are "req.host", which is the Host, "conn.client_ip", and "req.headers['x-example-header-name']" or the related macro getReqHeader('X-Example-Header-Name'), which is the value for the specified header key, if it exists. Up to ten bucket keys can be specified.

Supported Directions

• inbound
• outbound

Supported Schemes

• https
• http

Behavior

Determining the Rate Limit Bucket

When this action is executed, information from the incoming HTTP request is used to determine which rate limit bucket the request falls into. Each bucket is defined by specific criteria through the bucket_key configuration field such as client IP, request host, or a header value.

If the bucket has not exceeded its capacity, the request proceeds to the next action in your policy configuration.

Rate Limit Exceeded

If the identified bucket has received more events than its capacity over the specified duration:

1. The request is rejected with an HTTP 429 — Too Many Requests status code.
2. The retry-after header is included in the response, indicating the number of seconds after which the request may be retried.

Capacity per Ingress Server

Currently, the capacity for each rate limit bucket is applied per ingress server. This means that each server independently tracks the number of requests and enforces the rate limits accordingly.

Examples

Rate Limit by Host Header

The following Traffic Policy configuration demonstrates how to use the rate-limit action to rate limit all incoming requests by the Host header.

Example Traffic Policy Document

YAML

---
inbound:
  - actions:
      - type: "rate-limit"
        config:
          name: "Only allow 30 requests per minute"
          algorithm: "sliding_window"
          capacity: 30
          rate: "60s"
          bucket_key:
            - "req.headers['host']"

JSON

{
  "inbound": [
    {
      "actions": [
        {
          "type": "rate-limit",
          "config": {
            "name": "Only allow 30 requests per minute",
            "algorithm": "sliding_window",
            "capacity": 30,
            "rate": "60s",
            "bucket_key": [
              "req.headers['host']"
            ]
          }
        }
      ]
    }
  ]
}

For this example, we are assuming that ngrok is pointing at the upstream service https://httpbin.org.

Example Request

$ curl https://httpbin.ngrok.app/get

HTTP/2 429
retry-after: 24

In this example, we attempt to connect to httpbin.ngrok.app using the curl command and get back a 429 status code with a retry-after header telling us the number of seconds we must wait before retrying the request.

Action Result Variables

The following variables are made available for use in subsequent expressions and CEL interpolations after the action has run. Variable values will only apply to the last action execution, results are not concatenated.

Name	Type	Description
actions.ngrok.rate_limit.bucket_key	string	The key used for bucketing requests.
actions.ngrok.rate_limit.limited	boolean	True if the request was limited.
actions.ngrok.rate_limit.error.code	string	Code for an error that occurred during the invocation of an action.
actions.ngrok.rate_limit.error.message	string	Message for an error that occurred during the invocation of an action.