Describe different user-data file formats

user-data-file.md

@@ -1,8 +1,22 @@
-# Modules That Tiny-Cloud Supports
+# User Data
 
-The `user-data` file is used to configure Alpine linux state at the boot time. It supports a variety of modules that can be used to install packages, configure users and groups, and more. Tiny-cloud supports following modules:
+User-data file is loaded during early stage. Location of this file defined by kernel paramter: `ds=<provider>;s=<path>`. For example for nocloud provider: `ds=nocloud;s=http://my.miniserve.instance/tinycloud/` tiny cloud will search for a file with name "user-data" at http://my.miniserve.instance/tinycloud/ resource.
+
+Tiny-Cloud currently supports several user-data types and you could use ONE of them:
+
+- alpine-config
+- cloud-config
+- script
+
+The `user-data` file is used to configure Alpine Linux state at the boot time. It supports a variety of modules that can be used to install packages, configure users and groups, and more.
+
+## Alpine-Config Data Type
+
+Alpine config Must have `#alpine-config` as fist line in the file.
+Rest of the file is a yaml which describes several alpine-spesific configuration paramters:
 
 ```yaml
+#alpine-config
 apk:
   cache: # path to apk cache where /etc/apk/cache link follows
   repositories: # <map> defines resulted url https://dl-cdn.alpinelinux.org/alpine/edge/community
@@ -11,9 +25,22 @@ apk:
       repos: # <list>
         - community
 
-user: # <map> Sets default user
+autoinstall: # [ true | false] install alpine on the biggest empty disk found in the system
+```
+
+## Cloud-Config Data Type
+
+Alpine config Must have `#cloud-config` as fist line in the file.
+
+```yaml
+#cloud-config
+user: # <map> sets default user
   name: # <string>
 
+groups: # <list> groups for default user
+  - wheel
+  - admin
+
 users: # <list>
   # first one become default user
   - name:
@@ -25,10 +52,9 @@ users: # <list>
     no_create_home: # [ true | false ] do not create home directory for the user. Default: false
     lock_passwd: # reset password of the user
     ssh_authorized_keys: # <list>
-    groups: # <list>
-      - wheel
-      - power
-    doas: # content of the /etc/doas.d/<name> doas file
+    groups: wheel,power # comma-separated list of groups for the user
+    doas: # content of the /etc/doas.d/<name>.conf doas file
+      -
 
 ssh_authorized_keys: # public key to be authorized as default user
 
@@ -53,8 +79,15 @@ package_upgrade: # if "true" runs `apk upgrade`
 packages: # <list>
   - curl
   - bash
-
-groups: # <list>
-  - wheel
-  - admin
+```
+
+## Script Data Type
+
+Scipt user-data could be used to run arbitrary user script at the system init. User-data file must have script executor specific shebang, started with `#!`
+For example shell script:
+
+```shell
+#!/bin/sh
+
+echo "running custom script at init time"
 ```