Proxyless gRPC limitations

This document describes limitations that apply to Traffic Director with proxyless gRPC applications. For information about limits, see Quotas and limits.

General limitations

The limitations of Traffic Director with proxyless gRPC applications include the following:

  • You cannot configure backend services and routing rule maps with the gRPC protocol in the Google Cloud Console. For these resources, the Cloud Console is read-only.

  • Proxyless gRPC supports endpoint discovery, routing, load balancing, and load reporting.

    • For the minimum gRPC version required to support some advanced traffic management features, see Supported gRPC versions and languages.

    • If you need unsupported advanced traffic management features, configure your gRPC clients to use proxyless gRPC services only for a subset of services. To communicate with servers that require functionality that proxyless gRPC services do not yet support, use sidecar proxies.

  • In gRPC, only round-robin load balancing is supported. Other load-balancing algorithms are not supported.

    • Traffic Director provides a prioritized weighted list of localities—one instance group or one network endpoint group (NEG)—to the gRPC client. Traffic Director calculates this list based on the closest available zone, its capacity, and the balancing mode of the backend service.
    • For a particular request, the gRPC client picks one or more localities based on the priority and weight and does round-robin load balancing to the backends within those localities.
  • The failover from one zone (locality) to another starts when the current zone capacity falls below 50%. You can't configure this threshold.

  • In some cases, the configuration commands related to a target gRPC proxy and a forwarding rule that references a target gRPC proxy might take up to a minute.

URL map limitations

The following URL map traffic management features are supported with proxyless gRPC services:

  • hostrules
  • Features supported in pathMatcher of hostRules:
    • name
    • description
    • defaultService
    • defaultRouteAction
    • weightedBackendServices
      • backendService
      • weight
    • pathRules
    • service
    • routeAction
      • weightedBackendServices
        • backendService
        • weight
    • paths
    • routeRules
    • priority
    • description
    • matchRules
      • prefixMatch
      • fullPathMatch
      • headerMatches
    • service
    • routeAction
      • weightedBackendServices
        • backendService
        • weight

The following URL map limitations apply when you use proxyless gRPC services:

  • Wildcard characters in the host rules and default rules of a URL map, including the implicitly created * host rule of a URL map, are not supported. Such entries are skipped when host matching is done.

  • The following features are not supported:

    • queryParameterMatches in routeRules
    • headerAction, urlRewrite, retryPolicy, requestMirrorPolicy, corsPolicy, and urlRedirect route actions.
    • The defaultService, defaultRouteAction, defaultUrlRedirect and headerAction of the URL map are not used by proxyless gRPC services. If a matching host rule is not found when a proxyless gRPC client looks up a service name, Traffic Director returns a name lookup error instead of using the default service or action of the URL map.
    • headerAction in weightedBackendServices
  • In URL map header match rules, only non-binary user-specified custom metadata and the content-type header are supported. The following transport-level headers cannot be used in header matching rules: :authority, :method, :path, :scheme, user-agent, accept-encoding, content-encoding, grpc-accept-encoding, grpc-encoding, grpc-previous-rpc-attempts, grpc-tags-bin, grpc-timeout, and grpc-trace-bin.

  • When you update a URL map host rule to change from one backend service to another, traffic might be dropped momentarily while the new configuration is pushed to the clients. To avoid this limitation, configure traffic splitting with weighted backend services. After configuring traffic splitting, slowly shift traffic from the old backend service to the new backend service.

Target gRPC proxy limitations

When a target gRPC proxy references a URL map, you cannot configure the following URL map features whether you are using a sidecar proxy or a proxyless gRPC service. This is because the following HTTP protocol-specific features do not apply to the gRPC protocol:

  • queryParameterMatches match rule
  • urlRewrite route action
  • urlRedirect route action
  • corsPolicy action

Backend service limitations

The following backend service features are not supported with proxyless gRPC services that are supported with a sidecar proxy:

  • sessionAffinity
  • affinityCookieTtlSec
  • consistentHash
  • outlierDetection

Advanced traffic management limitations

You can't configure some advanced traffic management features for proxyless gRPC services with Traffic Director. For supported features, see the following:

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