Extension configuration

Each configuration resource in Envoy has a type URL in the typed_config. This type corresponds to a versioned schema. If the type URL uniquely identifies an extension capable of interpreting the configuration, then the extension is selected regardless of the name field. In this case the name field becomes optional and can be used as an identifier or as an annotation for the particular instance of the extension configuration. For example, the following filter configuration snippet is permitted:

name: front-http-proxy
typed_config:
  "@type": type.googleapis.com/envoy.extensions.filters.network.http_connection_manager.v3.HttpConnectionManager
  stat_prefix: ingress_http
  codec_type: AUTO
  rds:
    route_config_name: local_route
    config_source:
      resource_api_version: V3
      api_config_source:
        api_type: GRPC
        transport_api_version: V3
        grpc_services:
          envoy_grpc:
            cluster_name: xds_cluster
  http_filters:
  - name: front-router
    typed_config:
      "@type": type.googleapis.com/envoy.extensions.filters.http.router.v3.Router
      dynamic_stats: true

In case the control plane lacks the schema definitions for an extension, xds.type.v3.TypedStruct should be used as a generic container. The type URL inside it is then used by a client to convert the contents to a typed configuration resource. For example, the above example could be written as follows:

name: front-http-proxy
typed_config:
  "@type": type.googleapis.com/xds.type.v3.TypedStruct
  type_url: type.googleapis.com/envoy.extensions.filters.network.http_connection_manager.v3.HttpConnectionManager
  value:
    stat_prefix: ingress_http
    codec_type: AUTO
    rds:
      route_config_name: local_route
      resource_api_version: V3
      config_source:
        api_config_source:
          api_type: GRPC
          transport_api_version: V3
          grpc_services:
            envoy_grpc:
              cluster_name: xds_cluster
    http_filters:
    - name: front-router
      typed_config:
        "@type": type.googleapis.com/xds.type.v3.TypedStruct
        type_url: type.googleapis.com/envoy.extensions.filters.http.router.v3Router

Discovery service

Extension configuration can be supplied dynamically from an xDS management server using ExtensionConfiguration discovery service. The name field in the extension configuration acts as the resource identifier. For example, HTTP connection manager supports dynamic filter re-configuration for HTTP filters.

Extension config discovery service has a statistics tree rooted at <stat_prefix>.extension_config_discovery.<extension_config_name>. In addition to the common subscription statistics, it also provides the following:

Name	Type	Description
config_reload	Counter	Total number of successful configuration updates
config_fail	Counter	Total number of failed configuration updates
config_conflict	Counter	Total number of conflicting applications of configuration updates; this may happen when a new listener cannot reuse a subscribed extension configuration due to an invalid type URL.