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contrib/envoyproxy/go-control-plane/cmd/serviceextensions/README.md

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+# ASM Service Extension
+
+[GCP Services Extensions](https://cloud.google.com/service-extensions/docs/overview) enable Google Cloud users to provide programmability and extensibility on Cloud Load Balancing data paths and at the edge.
+
+## Installation
+
+### From Release
+
+This package provides a docker image to be used with Google Cloud Service Extensions.
+The images are published at each release of the tracer and can be found in [the repo registry](https://github.com/DataDog/dd-trace-go/pkgs/container/dd-trace-go%2Fservice-extensions-callout).
+
+### Build image
+
+The docker image can be build locally using docker. Start by cloning the `dd-trace-go` repo, `cd` inside it and run that command:
+```sh
+docker build --build-arg -f contrib/envoyproxy/go-control-plane/cmd/serviceextensions/Dockerfile -t datadog/dd-trace-go/service-extensions-callout:local .
+```
+
+## Configuration
+
+The ASM Service Extension expose some configuration. The configuration can be tweaked if the Service Extension is only used as an External Processor for Envoy that is not operated by GCP.
+
+>**GCP requires that the default configuration for the Service Extension should not change.**
+
+| Environment variable | Default value | Description |
+|---|---|---|
+| `DD_SERVICE_EXTENSION_HOST` | `0.0.0.0` | Host on where the gRPC and HTTP server should listen to. |
+| `DD_SERVICE_EXTENSION_PORT` | `443` | Port used by the gRPC Server.<br>Envoy Google backend’s is only using secure connection to Service Extension. |
+| `DD_SERVICE_EXTENSION_HEALTHCHECK_PORT` | `80` | Port used for the HTTP server for the health check. |
+
+> The Service Extension need to be connected to a deployed [Datadog agent](https://docs.datadoghq.com/agent).
+
+| Environment variable | Default value | Description |
+|---|---|---|
+| `DD_AGENT_HOST` | `N/A` | Host of a running Datadog Agent. |
+| `DD_TRACE_AGENT_PORT` | `8126` | Port of a running Datadog Agent. |
+
+### SSL Configuration
+
+The Envoy of GCP is configured to communicate to the Service Extension with TLS.
+
+`localhost` self signed certificates are generated and bundled into the ASM Service Extension docker image and loaded at the start of the gRPC server.