---
layout: docs
page_title: Send access logs to OpenTelemetry collector service
description: Learn how to use the `otel-access-logging` Envoy extension to send access logs to OpenTelemetry collector service.
---

# Send access logs to OpenTelemetry collector service

This topic describes how to use the OpenTelemetry Access Logging Envoy extension to send access logs to OpenTelemetry collector service.

## Workflow

Complete the following steps to use the OpenTelemetry access logging extension:

1. Configure an `EnvoyExtensions` block in a service defaults or proxy defaults configuration entry.
1. Apply the configuration entry.

## Add the `EnvoyExtensions`

Add Envoy extension configurations to a proxy defaults or service defaults configuration entry. Place the extension configuration in an `EnvoyExtensions` block in the configuration entry.

- When you configure Envoy extensions on proxy defaults, they apply to every service.
- When you configure Envoy extensions on service defaults, they apply to a specific service.

Consul applies Envoy extensions configured in proxy defaults before it applies extensions in service defaults. As a result, the Envoy extension configuration in service defaults may override configurations in proxy defaults.

The following example shows a service defaults configuration entry for the `api` service that directs the Envoy proxy to make gRPC OpenTelemetry access logging requests to the `otel-collector` service:

<CodeTabs tabs={[ "HCL", "JSON", "YAML" ]}>
<CodeBlockConfig filename="api-otel-collector-service-defaults.hcl">

```hcl
Kind = "service-defaults"
Name = "api"
EnvoyExtensions = [
  {
    Name = "builtin/otel-access-logging"
    Arguments = {
      ProxyType = "connect-proxy"
      Config = {
        GrpcService = {
          Target = {
            Service = {
              Name = "otel-collector"
            }
          }
        }
      }
    }
  }
]
```
</CodeBlockConfig>
<CodeBlockConfig filename="api-otel-collector-service-defaults.json">

```json
{
  "Kind": "service-defaults",
  "Name": "api",
  "EnvoyExtensions": [{
    "Name": "builtin/otel-access-logging",
    "Arguments": {
      "ProxyType": "connect-proxy",
      "Config": {
        "GrpcService": {
          "Target": {
            "Service": {
              "Name": "otel-collector"
            }
          }
        }
      }
    }
  }]
}
```

</CodeBlockConfig>
<CodeBlockConfig filename="api-otel-collector-service-defaults.yaml">

```yaml
apiVersion: consul.hashicorp.com/v1alpha1
kind: ServiceDefaults
metadata:
  name: api
  namespace: default
spec:
  envoyExtensions:
  - name: builtin/otel-access-logging
    arguments:
      proxyType: connect-proxy
      config:
        grpcService:
          target:
            service:
              name: otel-collector
              namespace: otel-collector
```

</CodeBlockConfig>
</CodeTabs>

Refer to the [OpenTelemetry Access Logging extension configuration reference](/consul/docs/reference/proxy/extensions/otel) for details on how to configure the extension.

Refer to the [proxy defaults configuration entry reference](/consul/docs/reference/config-entry/proxy-defaults) and [service defaults configuration entry reference](/consul/docs/reference/config-entry/service-defaults) for details on how to define the configuration entries.

<Warning>
  Adding Envoy extensions default proxy configurations may have unintended consequences. We recommend configuring `EnvoyExtensions` in service defaults configuration entries in most cases.
</Warning>

### Unsupported Envoy configuration fields

The following Envoy configurations are not supported:

| Configuration           | Workaround                                                                                                                     |
| ----------------------- | ------------------------------------------------------------------------------------------------------------------------------ |
| `transport_api_version` | Consul only supports v3 of the transport API. As a result, there is no workaround for implementing the behavior of this field. |

## Apply the configuration entry

If your network is deployed to virtual machines, use the `consul config write` command and specify the proxy defaults or service defaults configuration entry to apply the configuration. For Kubernetes-orchestrated networks, use the `kubectl apply` command. The following example applies the extension in a proxy defaults configuration entry.

<CodeTabs tabs={[ "HCL", "JSON", "YAML" ]}>

```shell-session
$ consul config write api-otel-collector-service-defaults.hcl
```

```shell-session
$ consul config write api-otel-collector-service-defaults.json
```

```shell-session
$ kubectl apply -f api-otel-collector-service-defaults.yaml
```

</CodeTabs>
