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Rate limiting extension

The Ambassador Edge Stack ships with a rate limiting service that is enabled to perform advanced rate limiting out of the box.

Configuration of the Mapping and RateLimit resources that control how to rate limit requests can be found in the Rate Limiting section of the documentation.

This document focuses on how to deploy and manage the rate limiting extension.

Ambassador configuration

Ambassador uses the RateLimitService plugin to connect to the rate limiting extension in the Ambassador Edge Stack.

The default RateLimitService is named ambassador-edge-stack-ratelimit and is defined as:

  • failure_mode_deny By default, Ambassador Edge Stack will fail open when unable to communicate with the service due to it becoming unvailable or due to timeouts. When this happens the upstream service that is being protected by a rate limit may be overloaded due to this behavior. When set to true Ambassador Edge Stack will be configured to return a 500 status code when it is unable to communicate with the RateLimit service and will fail closed by rejecting request to the upstream service.
  • grpc contains settings for grpc connections
    • use_resource_exhausted_code By default, Ambassador Edge Stack will return an UNAVAILABLE gRPC code when a request is rate limited. When set to true, this field will cause Ambassador Edge Stack will return a RESOURCE_EXHAUSTED gRPC code instead.

This configures Envoy to send requests that are labeled for rate limiting to the extension process running on port 8500. The rate limiting extension will then use that request to count against any RateLimit whose pattern matches the request labels.

Authentication extension configuration

Certain use cases may require some tuning of the rate limiting extension. Configuration of this extension is managed via environment variables. The Ambassador Container has a full list of environment variables available for configuration. This document highlights the ones used by the rate limiting extension.


The rate limiting extension relies heavily on redis for writing and reading counters for the different RateLimit patterns.

The Ambassador Edge Stack shares the same Redis pool for all features that use Redis.

See the Redis documentation for information on Redis tuning.


If REDIS_PERSECOND is true, a second Redis connection pool is created (to a potentially different Redis instance) that is only used for per-second RateLimits; this second connection pool is configured by the REDIS_PERSECOND_* variables rather than the usual REDIS_* variables.


Set AES_RATELIMIT_PREVIEW to true to access support for redis clustering, local caching, and an upgraded redis client with improved scalability in preview mode.


Only available if AES_RATELIMIT_PREVIEW: "true.

The AES rate limit extension can optionally cache over-the-limit keys so it does not need to read the redis cache again for requests with labels that are already over the limit.

Setting LOCAL_CACHE_SIZE_IN_BYTES to a non-zero value with enable local caching.


Only available if AES_RATELIMIT_PREVIEW: "true"

Adjusts the ratio used by the near_limit statistic for tracking requests that are "near the limit".

Defaults to 0.8 (80%) of the limit defined in the RateLimit rule.