User Data is a way to automatically provision your machine with additional software or settings. You can provide a set of commands (ie. a script) or enter cloud-config information as YAML. It is important to understand that the User Data provided will be used only when the machine is created.

Adding User Data

When you’re creating a new instance, the wizard lets you enter User Data at the bottom of the form.

You can find everything that can be done with User Data and Cloud-Init in the documentation

Example: script

Let’s install screen and htop on an Ubuntu instance using Apt after having upgraded all packages on an Debian/Ubuntu system.

Add the following to the User Data field to install the screen package:

#cloud-config
runcmd:
    - apt-get --yes upgrade
    - apt-get --yes install screen htop

Note: Cloud-Init has pre-built directives for many items. Therefore, the previous scripts launched as command lines could be achieved with:

#cloud-config
package_upgrade: true
packages:
  - screen
  - htop

Example: cloud-config YAML

Let’s set our locale to en_US.UTF-8 using cloud-config YAML. Add the following YAML in the User Data:

#cloud-config
locale: "en_US.UTF-8"

Example: installing Wordpress

See our Wordpress tutorial

Querying the user data and meta data from the instance

User Data and Meta Data can be retrieved from an instance to integrate in scripts for example or configuration management tools. This information is published on the Link Local Address 169.254.169.254 which is private between the hypervisor and the running instance.

  • User Data (the cloud-config contents)
curl http://metadata.exoscale.com/latest/user-data
  • Meta Data, such as instance size or IP address
curl http://metadata.exoscale.com/latest/meta-data
curl http://metadata.exoscale.com/latest/meta-data/public-ipv4

Adding Password Management to Your Templates

Exoscale provides an optional password reset feature that allows users to set a temporary admin or root password as well as reset the existing admin or root password from the Exoscale Portal.

This password is provided to an instance via the Link Local Address 169.254.169.254 on port 8080

curl  --header "DomU_Request: send_my_password" http://169.254.169.254:8080

Once the password is retrieved and changed on the running instance, issue a command to indicate that the password was saved and that it can be deleted

curl  --header "DomU_Request: saved_password" http://169.254.169.254:8080

Notes:

  • Linux based distributions with a standard Cloud-Init implementation will follow automatically the above process if the system allows for password based logins.
  • Passwords are only provided once back to the user who starts or resets an instance and are not persisted at the orchestration layer