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| A77: xDS Server-Side Rate Limiting | ||
| ====== | ||
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| * Author(s): Sergii Tkachenko (sergiitk@) | ||
| * Approver: Mark Roth (@markdroth) | ||
| * Status: Draft | ||
| * Implemented in: | ||
| * Last updated: 2024-01-24 | ||
| * Discussion at: `TODO(sergiitk): <google group thread>` | ||
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| ## Abstract | ||
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| This proposal introduces support for the | ||
| [quota-based global rate limit](https://www.envoyproxy.io/docs/envoy/latest/configuration/http/http_filters/rate_limit_quota_filter) | ||
| feature to [xDS-Enabled gRPC servers][A36].\ | ||
| Main characteristics of the feature: | ||
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| * Only covers server-side rate limiting. | ||
| * Can only be applied to HTTP-level (L7) requests. | ||
| * Rate limit decisions are offloaded to a remote Rate Limit Quota Service (RLQS) | ||
| asynchronously. | ||
| * RLQS maintains a global view of the shared rate limit resource, and fairly | ||
| distributes it among multiple servers (best-effort). | ||
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| ## Background | ||
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| [Global rate limiting](https://www.envoyproxy.io/docs/envoy/latest/intro/arch_overview/other_features/global_rate_limiting) | ||
| allows mesh users to manage fair consumption of their services and prevent | ||
| misbehaving clients from overloading the services. *Global* rate limiting | ||
| implies that there must be a single source of truth for the state of a finite | ||
| shared resource; a Rate Limiting Service. As of 2024-01-24, Envoy describes two | ||
| types of such service: | ||
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| 1. [Rate Limiting Service (RLS)](https://www.envoyproxy.io/docs/envoy/latest/intro/arch_overview/other_features/global_rate_limiting#per-connection-or-per-http-request-rate-limiting): | ||
| synchronous (blocking) per-HTTP-request rate limit check. Best suited for | ||
| precise cases, where even a single request over the limit must be throttled. | ||
| 2. [Rate Limiting Quota Service (RLQS)](https://www.envoyproxy.io/docs/envoy/latest/intro/arch_overview/other_features/global_rate_limiting#quota-based-rate-limiting): | ||
| asynchronous (non-blocking) quota-based check, with periodic load reports of | ||
| bucketed HTTP requests. Best suited for high-request-per-second applications, | ||
| where a certain margin of error is acceptable as long as expected average QPS | ||
| is achieved. | ||
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| gRPC only intends to support quota-based global rate limiting, Rate Limiting | ||
| Quota Service (RLQS), which is described in this document. | ||
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| Simplified RLQS flow happy-path: | ||
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| 1. [Rate Limit Quota xDS HTTP filter][rate_limit_quota_filter] | ||
| is configured on a gRPC Server via an LDS update in the HTTP connection | ||
| manager filter chain. | ||
| 2. gRPC Server establishes a gRPC channel to the RLQS as specified | ||
| in [RateLimitQuotaFilterConfig.rlqs_server]. | ||
| 3. gRPC Server parses [RateLimitQuotaFilterConfig.bucket_matchers] tree and | ||
| caches it in the filter state. | ||
| 4. gRPC Server installs a Server Interceptor (filter in C-core, later called | ||
| "the Interceptor" for simplicity) | ||
| 5. Once a request is intercepted by the Interceptor: | ||
| 1. The request is matched into a Bucket by evaluating the `bucket_matchers` | ||
| tree against the request attributes. | ||
| 2. If the Bucket doesn't exist, gRPC server immediately sends the | ||
| initial `BucketQuotaUsage` report to the RLQS server. The request is | ||
| throttled according | ||
| to [RateLimitQuotaBucketSettings.no_assignment_behavior]. | ||
| 3. If the Bucket exists, the request is throttled according to Bucket's | ||
| quota assignment. Bucket's `num_requests_allowed` | ||
| or `num_requests_denied` request counter is increased by one. | ||
| 6. For all existing buckets, a `BucketQuotaUsage` report is sent | ||
| every [RateLimitQuotaBucketSettings.reporting_interval] | ||
| to `RateLimitQuotaService.StreamRateLimitQuotas`. | ||
| 7. RLQS may send Bucket quota assignments via `RateLimitQuotaResponse` at any | ||
| time. Once received, it must the quota must be applied to a Bucket with | ||
| matching [bucket_id]. | ||
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| ### Related Proposals: | ||
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| * [A36: xDS-Enabled Servers][A36] | ||
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| [A36]: A36-xds-for-servers.md | ||
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| ## Proposal | ||
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| TODO(sergiitk): A precise statement of the proposed change. | ||
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| ### Temporary environment variable protection | ||
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| During initial development, this feature will be enabled via the | ||
| `GRPC_EXPERIMENTAL_XDS_ENABLE_RLQS` environment variable. This environment | ||
| variable protection will be removed once the feature has proven stable. | ||
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| ## Rationale | ||
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| TODO(sergiitk): A discussion of alternate approaches and the trade offs, | ||
| advantages, and disadvantages of the specified approach. | ||
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| ## Implementation | ||
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| The initial implementation will be in Java.\ | ||
| C-core, Python, and Go will follow after that. | ||
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| ## Open issues (if applicable) | ||
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| TODO(sergiitk): A discussion of issues relating to this proposal for which the | ||
| author does not know the solution. This section may be omitted if there are | ||
| none. | ||
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| <!-- Reference links --> | ||
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| [rate_limit_quota_filter]: https://www.envoyproxy.io/docs/envoy/latest/configuration/http/http_filters/rate_limit_quota_filter | ||
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| [RateLimitQuotaBucketSettings.domain]: https://www.envoyproxy.io/docs/envoy/latest/api-v3/extensions/filters/http/rate_limit_quota/v3/rate_limit_quota.proto.html#envoy-v3-api-field-extensions-filters-http-rate-limit-quota-v3-ratelimitquotafilterconfig-domain | ||
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| [RateLimitQuotaBucketSettings.no_assignment_behavior]: https://www.envoyproxy.io/docs/envoy/latest/api-v3/extensions/filters/http/rate_limit_quota/v3/rate_limit_quota.proto#envoy-v3-api-field-extensions-filters-http-rate-limit-quota-v3-ratelimitquotabucketsettings-no-assignment-behavior | ||
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| [RateLimitQuotaBucketSettings.reporting_interval]: https://www.envoyproxy.io/docs/envoy/latest/api-v3/extensions/filters/http/rate_limit_quota/v3/rate_limit_quota.proto#envoy-v3-api-field-extensions-filters-http-rate-limit-quota-v3-ratelimitquotabucketsettings-reporting-interval | ||
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| [RateLimitQuotaFilterConfig.rlqs_server]: https://www.envoyproxy.io/docs/envoy/latest/api-v3/extensions/filters/http/rate_limit_quota/v3/rate_limit_quota.proto#envoy-v3-api-field-extensions-filters-http-rate-limit-quota-v3-ratelimitquotafilterconfig-rlqs-server | ||
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| [RateLimitQuotaFilterConfig.bucket_matchers]: https://www.envoyproxy.io/docs/envoy/latest/api-v3/extensions/filters/http/rate_limit_quota/v3/rate_limit_quota.proto#envoy-v3-api-field-extensions-filters-http-rate-limit-quota-v3-ratelimitquotafilterconfig-bucket-matchers | ||
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| [bucket_id]: https://www.envoyproxy.io/docs/envoy/latest/api-v3/service/rate_limit_quota/v3/rlqs.proto#envoy-v3-api-field-service-rate-limit-quota-v3-ratelimitquotaresponse-bucketaction-bucket-id |