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Rate Limiting

Local Rate Limiting

The HTTPProxy API supports defining local rate limit policies that can be applied to either individual routes or entire virtual hosts. Local rate limit policies define a maximum number of requests per unit of time that an Envoy should proxy to the upstream service. Requests beyond the defined limit will receive a 429 (Too Many Requests) response by default. Local rate limit policies program Envoy’s HTTP local rate limit filter.

It’s important to note that local rate limit policies apply per Envoy pod. For example, a local rate limit policy of 100 requests per second for a given route will result in each Envoy pod allowing up to 100 requests per second for that route.

By contrast, global rate limiting (which will be added in a future Contour release), uses a shared external rate limit service, allowing rate limits to apply across all Envoy pods.

Defining a local rate limit

Local rate limit policies can be defined for either routes or virtual hosts. A local rate limit policy requires a requests and a units field, defining the number of requests per unit of time that are allowed. Requests must be a positive integer, and units can be second, minute, or hour. Optionally, a burst parameter can also be provided, defining the number of requests above the baseline rate that are allowed in a short period of time. This would allow occasional larger bursts of traffic not to be rate limited.

Local rate limiting for the virtual host:

apiVersion: projectcontour.io/v1
kind: HTTPProxy
metadata:
  namespace: default
  name: ratelimited-vhost
spec:
  virtualhost:
    fqdn: local.projectcontour.io
    rateLimitPolicy:
    local:
      requests: 100
      unit: hour
      burst: 20
  routes:
  - conditions:
    - prefix: /s1
    services:
    - name: s1
      port: 80
  - conditions:
    - prefix: /s2
    services:
    - name: s2
      port: 80

Local rate limiting for the route:

apiVersion: projectcontour.io/v1
kind: HTTPProxy
metadata:
  namespace: default
  name: ratelimited-route
spec:
  virtualhost:
    fqdn: local.projectcontour.io
  routes:
  - conditions:
    - prefix: /s1
    services:
    - name: s1
      port: 80
    rateLimitPolicy:
      local:
        requests: 20
        unit: minute
  - conditions:
    - prefix: /s2
    services:
    - name: s2
      port: 80

Customizing the response

Response code

By default, Envoy returns a 429 (Too Many Requests) when a request is rate limited. A non-default response code can optionally be configured as part of the local rate limit policy, in the responseStatusCode field. The value must be in the 400-599 range.

apiVersion: projectcontour.io/v1
kind: HTTPProxy
metadata:
  namespace: default
  name: custom-ratelimit-response
spec:
  virtualhost:
    fqdn: local.projectcontour.io
  routes:
  - conditions:
    - prefix: /s1
    services:
    - name: s1
      port: 80
    rateLimitPolicy:
      local:
        requests: 20
        unit: minute
        responseStatusCode: 503 # Service Unavailable 

Headers

Headers can optionally be added to rate limited responses, by configuring the responseHeadersToAdd field.

apiVersion: projectcontour.io/v1
kind: HTTPProxy
metadata:
  namespace: default
  name: custom-ratelimit-response
spec:
  virtualhost:
    fqdn: local.projectcontour.io
  routes:
  - conditions:
    - prefix: /s1
    services:
    - name: s1
      port: 80
    rateLimitPolicy:
      local:
        requests: 20
        unit: minute
        responseHeadersToAdd:
        - name: x-contour-ratelimited
          value: "true"

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