Static Rate Limiting

Overview

When exposing an API to the public, it is critical to protect it from potential abuse by heavy hitters and malicious users. This ensures that the API remains available and performs optimally for all users. Aperture's rate limiter identifies users in the traffic using labels in the request. Distributed token buckets are maintained for each user, ensuring that each user stays within the assigned limits. The token bucket is configured with a fill rate that determines the maximum request rate in steady state. The bucket's capacity determines the magnitude of momentary surge allowed in request rates.

Configuration

This example applies a rate limiter to the ingress control point on the service catalog-service.prod.svc.cluster.local. Unique users are identified based on the user_id header in the HTTP traffic. This header is provided by the Envoy proxy and is available under the label key http.request.header.user_id (see Flow Labels for more information).

Each user is allowed 2 requests every 1s (1 second) period. A burst of up to 40 requests is allowed. This means that the user can send up to 40 requests in the first second, and then 2 requests every second after that. The bucket gets replenished at the rate of 2 requests per second (the fill rate).

aperturectl values.yaml

# yaml-language-server: $schema=../../../../../../blueprints/policies/rate-limiting/gen/definitions.json
policy:
  policy_name: "static-rate-limiting"
  rate_limiter:
    bucket_capacity: 40
    fill_amount: 2
    selectors:
      - service: "catalog-service.prod.svc.cluster.local"
        control_point: "ingress"
        agent_group: "default"
    parameters:
      label_key: "http.request.header.user_id"
      interval: 1s

Generated Policy

apiVersion: fluxninja.com/v1alpha1
kind: Policy
metadata:
  annotations:
    fluxninja.com/blueprint-name: policies/rate-limiting
    fluxninja.com/blueprints-uri: local
    fluxninja.com/values:
      '{"policy": {"policy_name": "static-rate-limiting", "rate_limiter":
      {"bucket_capacity": 40, "fill_amount": 2, "parameters": {"interval": "1s", "label_key":
      "http.request.header.user_id"}, "selectors": [{"agent_group": "default", "control_point":
      "ingress", "service": "catalog-service.prod.svc.cluster.local"}]}}}'
  labels:
    fluxninja.com/validate: "true"
  name: static-rate-limiting
spec:
  circuit:
    components:
      - flow_control:
          rate_limiter:
            in_ports:
              bucket_capacity:
                constant_signal:
                  value: 40
              fill_amount:
                constant_signal:
                  value: 2
            parameters:
              interval: 1s
              label_key: http.request.header.user_id
            selectors:
              - agent_group: default
                control_point: ingress
                service: catalog-service.prod.svc.cluster.local
    evaluation_interval: 10s
  resources:
    flow_control:
      classifiers: []

info

Circuit Diagram for this policy.

Policy in Action

When the policy is applied at a service, no more than 2 requests per second period (after an initial burst of 40 requests) are accepted for a user.