docs: document user data on create compute

api-reference/endpoint/create-compute.mdx

@@ -40,6 +40,37 @@ Use these slugs for the `region`, `image`, and `specification` fields in your re
 
 ---
 
+### User Data
+
+Pass your own [cloud-init](https://cloudinit.readthedocs.io/) configuration in `userData` to set up the instance on its first boot: install packages, write files, create users or run a script. Send a `#cloud-config` file or a shell script starting with `#!`. It works with every image.
+
+- Encode it as standard base64, on one line.
+- It can be at most 32 KiB after decoding.
+- It's optional. Leave it out and the instance is created as usual.
+
+```bash
+USER_DATA=$(printf '#cloud-config\npackages:\n  - nginx\n' | base64 | tr -d '\n')
+
+curl -X POST https://api.strettch.cloud/api/v1/computes \
+  -H "Authorization: Bearer $STRETTCH_API_KEY" \
+  -H "Content-Type: application/json" \
+  -H "Idempotency-Key: $(uuidgen)" \
+  -d '{
+    "hostName": "web-01",
+    "image": "UBUNTU-24.04",
+    "region": "KGL-1",
+    "specification": "S-1C-1G",
+    "publicKeys": ["ssh-ed25519 AAAA... you@laptop"],
+    "userData": "'"$USER_DATA"'"
+  }'
+```
+
+<Note>
+  The instance receives the data exactly as you sent it. Where your cloud-config and Strettch Cloud's defaults set the same key, your value wins.
+</Note>
+
+---
+
 ### Response Error Codes
 
 If the request fails, the `code` field in the error response will contain one of the following.

api-reference/openapi.json

@@ -1047,6 +1047,12 @@
               "web"
             ]
           },
+          "userData": {
+            "description": "Optional cloud-init user data: a #cloud-config file or a shell script starting with #!, base64 encoded, at most 32 KiB after decoding. The instance receives it unchanged on its first boot.",
+            "type": "string",
+            "contentEncoding": "base64",
+            "example": "I2Nsb3VkLWNvbmZpZwpwYWNrYWdlczoKICAtIG5naW54Cg=="
+          },
           "withPublicIp": {
             "type": "boolean",
             "example": true

skills/strettch-cloud/SKILL.md

@@ -92,6 +92,7 @@ Body:
 | `publicKeys` | string[] | Yes (min 1) | SSH public keys for access |
 | `withPublicIp` | boolean | No | Allocate a public IP address |
 | `tags` | string[] | No | Labels for the instance |
+| `userData` | string (base64) | No | cloud-init user data (`#cloud-config` or a `#!` script), at most 32 KiB decoded |
 
 ### Upsize Compute Request (PATCH /computes/{id}/upsize)