Add userdata

Signed-off-by: Arnaud M. <arnaud.choupinette@mailops.fr>

cloud/training/101.md

@@ -13,6 +13,7 @@
     * [Boot](#boot-1)
     * [Floating IP](#floating-ip)
     * [Connect with ssh](#connect-with-ssh-1)
+  * [Userdata](#userdata)
   * [Bonus](#bonus)
 
 
@@ -292,11 +293,33 @@ ssh debian@xxx.yyy.zzz.aaa  # floating ip
 
 Q: what IP can you see on ens3 interface of the instance?
 
+## Userdata
+
+### Create a script
+Create a file named `postinstall.sh` with this content:
+```
+#!/bin/bash
+
+echo "Hello from my instance" > /var/log/postinstall.log
+```
+
+### Start an instance
+Figure out the command to start a new instance with this script as `user-data`.
+
+Don't forget to start with your `keypair` so you can connect to it later
+
+### Check the result
+When the instance is booted, ssh into it and check the result of the file:
+
+```
+cat /var/log/postinstall.log
+```
+
+## demo-flask
+
+Try to deploy `demo-flask` with a custom `user-data` script.
+
+
 ## Bonus
 
-Try to deploy `demo-flask` with cloud-init
-
-
-## Bonus 2
-
 Take a look at the [skyline WebUI](http://skyline.54.36.119.253.xip.opensteak.fr) and try to boot another instance from there.