docs(em): add cloud-init

pages/elastic-metal/concepts.mdx

@@ -3,11 +3,37 @@ title: Elastic Metal - Concepts
 description: This page explains all the concepts related to Scaleway Elastic Metal servers
 tags: elastic-metal rescue-mode private-networks remote-access az
 dates:
-  validation: 2025-08-27
+  validation: 2025-11-03
 ---
 import RegionAndAz from '@macros/console/region-and-az.mdx'
 
 
+## Cloud-init
+
+**Cloud-init** is a widely used tool that automates the initial configuration of Elastic Metal servers at boot time. It allows users to define and execute custom setup instructions, transforming a generic operating system image into a fully configured dedicated machine within seconds.
+
+When an Elastic Metal server is launched, `cloud-init` reads user-provided configuration data (also known as *user-data*) and applies it during the boot process. This enables tasks such as installing packages, creating users, configuring SSH keys, or running shell scripts automatically, without manual intervention.
+
+### Cloud-init user-data
+
+User-data is the mechanism through which configuration instructions are passed to an Instance. When cloud-init detects user-data during boot, it interprets and executes it based on the data format provided.
+The following formats are supported:
+
+| Format                      | Starts with       | Description                                                      |
+| --------------------------- | ----------------- | ---------------------------------------------------------------- |
+| **Cloud config file**       | `#cloud-config`   | YAML file containing cloud-init configuration directives.        |
+| **Shell script**            | `#!`              | Shell script executed during the first boot of the Instance.     |
+| **Include file**            | `#include`        | File listing URLs whose contents will be fetched and executed.   |
+| **Gzip compressed content** | N/A               | Gzip-compressed user-data that is decompressed and executed.     |
+| **MIME multipart archive**  | N/A               | File combining multiple data types (e.g. cloud-config + script). |
+| **Upstart job**             | `#upstart-job`    | Upstart job to be executed during boot.                          |
+| **Cloud boothook**          | `#cloud-boothook` | Script executed very early in the boot process.                  |
+| **Part handler**            | `#part-handler`   | Custom handler for processing specific data parts.               |
+
+<Message type="note">
+  Only user-data with content type `text/plain` is currently supported on Scaleway.
+</Message>
+
 ## Elastic Metal server
 
 Scaleway Elastic Metal are dedicated physical servers you can order on-demand, like Instances. These servers can be used for large workloads, big data and applications that require increased security and dedicated resources.

pages/elastic-metal/how-to/create-server.mdx

@@ -35,6 +35,7 @@ Scaleway [Elastic Metal servers](https://www.scaleway.com/en/elastic-metal/) pro
     - Select a server configuration from the available options.
     - Choose an OS to run on your server or opt for no preinstalled image.
     - Configure server partitioning. You can either choose a default configuration or [configure your own partitioning](/elastic-metal/how-to/configure-disk-partitions/).
+    - Optionally, enable and configure cloud-init. Cloud-init is a widely adopted standard for customizing dedicated servers. [Learn more](/elastic-metal/concepts/#cloud-init).
     - Enter a name and, optionally, add tags to identify your server.
     - Add your SSH key (required if installing an image on your server). Depending on the OS image, you may also be asked to configure the panel user for your server.
     - Optionally, configure the available public bandwidth for your server. This option may not be available for all offers.