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RateLimitService Plugin

Rate limiting is a powerful technique to improve the availability and resilience of your services. In Ambassador, each request can have one or more labels. These labels are exposed to a third-party service via a gRPC API. The third-party service can then rate limit requests based on the request labels.

Note that RateLimitService is only applicable to the Ambassador API Gateway, and not the Ambassador Edge Stack, as the Ambassador Edge Stack includes a built-in rate limit service.

Request Labels

Ambassador lets users add one or more labels to a given request. These labels are added as part of a Mapping object. For example:

---
apiVersion: getambassador.io/v2
kind:  Mapping
metadata:
  name:  catalog
spec:
  prefix: /catalog/
  service: catalog
  request_labels:
    - service: catalog

For more information on request labels, see the Rate Limit reference.

Domains

In Ambassador, each engineer (or team) can be assigned its own domain. A domain is a separate namespace for labels. By creating individual domains, each team can assign their own labels to a given request, and independently set the rate limits based on their own labels.

Default labels

Ambassador allows setting a default label on every request. A default label is set on the ambassador Module. For example:

---
apiVersion: getambassador.io/v2
kind:  Module
metadata:
  name:  ambassador
spec:
  config:
    default_label_domain: ambassador
    default_labels:
      ambassador:
        defaults:
        - remote_address

External Rate Limit Service

In order for the Ambassador API Gateway to rate limit, you need to implement a gRPC RateLimitService, as defined in Envoy's v1/rls.proto interface. If you do not have the time or resources to implement your own rate limit service, the Ambassador Edge Stack integrates a high-performance rate limiting service.

Note: In a future version of Ambassador, the Ambassador API Gateway will change the version of the gRPC service name used to communicate RateLimitServices from the one defined in v1/rls.proto (pb.lyft.ratelimit.RateLimitService) to the one defined in v2/rls.proto (envoy.service.ratelimit.v2.RateLimitService):

  • In some future version of Ambassador, there will be a setting to control which name is used; with the default being the current name; it will be opt-in to the new name.

  • In some future version of Ambassador after that, no sooner than Ambassador 1.7.0, the default value of that setting will change; making it opt-out from the new name.

  • In some future version of Ambassador after that, no sooner than Ambassador 1.8.0, the setting will go away, and Ambassador will always use the new name.

In the meantime, implementations of RateLimitService are encouraged to respond to both names--they are simply aliases of eachother, registering the service under both names is usually a simple 1-or-2-line addition. For example, in Go the change to support both names is:

import (
    envoy_ratelimit_v1 "github.com/datawire/ambassador/pkg/api/envoy/service/ratelimit/v1"
+   envoy_ratelimit_v2 "github.com/datawire/ambassador/pkg/api/envoy/service/ratelimit/v2"
 )
...
    envoy_ratelimit_v1.RegisterRateLimitServiceServer(myGRPCServer, myRateLimitImplementation)
+   envoy_ratelimit_v2.RegisterRateLimitServiceServer(myGRPCServer, myRateLimitImplementation)

The Ambassador API Gateway generates a gRPC request to the external rate limit service and provides a list of labels on which the rate limit service can base its decision to accept or reject the request:

[
  {"source_cluster", "<local service cluster>"},
  {"destination_cluster", "<routed target cluster>"},
  {"remote_address", "<trusted address from x-forwarded-for>"},
  {"generic_key", "<descriptor_value>"},
  {"<some_request_header>", "<header_value_queried_from_header>"}
]

If the Ambassador API Gateway cannot contact the rate limit service, it will allow the request to be processed as if there were no rate limit service configuration.

It is the external rate limit service's responsibility to determine whether rate limiting should take place, depending on custom business logic. The rate limit service must simply respond to the request with an OK or OVER_LIMIT code:

  • If Envoy receives an OK response from the rate limit service, then the Ambassador API Gateway allows the client request to resume being processed by the normal flow.
  • If Envoy receives an OVER_LIMIT response, then the Ambassador API Gateway will return an HTTP 429 response to the client and will end the transaction flow, preventing the request from reaching the backing service.

The headers injected by the AuthService can also be passed to the rate limit service since the AuthService is invoked before the RateLimitService.

Configuring the Rate Limit Service

A RateLimitService manifest configures the Ambassador API Gateway to use an external service to check and enforce rate limits for incoming requests:

---
apiVersion: getambassador.io/v2
kind:  RateLimitService
metadata:
  name:  ratelimit
spec:
  service: "example-rate-limit:5000"
  • service gives the URL of the rate limit service.

You may only use a single RateLimitService manifest.

Rate Limit Service and TLS

You can tell the Ambassador API Gateway to use TLS to talk to your service by using a RateLimitService with an https:// prefix. However, you may also provide a tls attribute: if tls is present and true, the Ambassador API Gateway will originate TLS even if the service does not have the https:// prefix.

If tls is present with a value that is not true, the value is assumed to be the name of a defined TLS context, which will determine the certificate presented to the upstream service.

Example

The Ambassador API Gateway Rate Limiting Tutorial has a simple rate limiting example. For a more advanced example, read the advanced rate limiting tutorial, which uses the rate limit service that is integrated with the Ambassador Edge Stack.

Further Reading

Questions?

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