# 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:
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:
dynamic_stats: true


In case the control plane lacks the schema definitions for an extension, udpa.type.v1.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:
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:


## 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