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> [!NOTE]
> **Note:** Apigee Extensions are available in the Edge UI to Google Cloud Apigee customers with an Enterprise [support](https://cloud.google.com/apigee/pricing) plan.

An [extension](https://docs.apigee.com/api-platform/extensions/extensions-overview) is a kind of bridge
between your API proxies and an external resource. This tutorial shows you what an extension is,
and guides you through the required processes.

## Prerequisites

Before you start this tutorial, make sure you've done all of the following:

| Area | Steps | Done? |
|---|---|---|
| **Apigee Edge** | Apigee must enable the extensions feature for your Apigee Public Cloud organization. If the feature is enabled, you will see an **Extensions** menu item in the **Admin** menu of the Edge UI. If not, please contact [Apigee Edge Support](https://docs.apigee.com/api-platform/troubleshoot/support). |   |
| **Google Cloud Platform** | 1. Create a project on [Google Cloud Platform](https://console.cloud.google.com/), if you don't already have one. Your API proxy will write log entries using this project. 2. Create a Workspace for your Google Cloud project as described in [Creating a Workspace](https://cloud.google.com/monitoring/workspaces/manage#single-project-ws). |   |
| **Service Account** | 1. Create or choose a Google Cloud Service Account (SA) with which we'll authenticate to Google Cloud. You can create an SA in the Google Cloud console at **IAM \& Admin \> Service accounts**. 2. Assign the **Logs Writer** role to the SA in **Logging \> Logs Writer** . For more information, see [Granting roles to a service account for specific resources](https://cloud.google.com/iam/docs/granting-roles-to-service-accounts#granting_access_to_a_service_account_for_a_resource). 3. Download an SA JSON file for configuring the extension. For more information see [Creating and managing service account keys](https://cloud.google.com/iam/docs/creating-managing-service-account-keys). |   |

## Ready? Let's begin!

To use extensions with Apigee Edge:

1. **[Step 1: Add an extension to Edge](https://docs.apigee.com/api-platform/tutorials/add-extension/add-new-extension).**
2. **[Step 2: Configure and deploy for testing](https://docs.apigee.com/api-platform/tutorials/add-extension/configure-for-testing).**
3. **[Step 3: Use an ExtensionCallout policy](https://docs.apigee.com/api-platform/tutorials/add-extension/extension-callout-policy).**
4. **[Step 4: Deploy your proxy](https://docs.apigee.com/api-platform/tutorials/add-extension/proxy-deployment).**
5. **[Step 5: Log a message flow variable](https://docs.apigee.com/api-platform/tutorials/add-extension/xtra-credit).**