How to configure an OpenStack instance using cloud-config

Overview

When you boot an instance in OpenStack you can pass configuration to the instance as cloud-config (sometimes called user-data). This enables you to quickly and easily make configuration changes at boot time.

Use cases

The following list provides some examples of how you can use cloud-config to configure an instance:

  • Setting a default locale
  • Setting an instance hostname
  • Generating instance SSH private keys
  • Adding SSH keys to a user's .ssh/authorized_keys so they can log in
  • Setting up ephemeral mount points
  • Configuring network devices
  • Running config scripts at startup

Example

You can deploy cloud-config via the command line or via the OpenStack Horizon GUI. In this guide, we use the CLI, but you can use the same script via the GUI by pasting it into the Configuration tab.

As an example, let's boot an instance and run some arbitrary commands at boot time.

  1. Create a new text file called user-data.txt.

  2. Add the following to the new file.

    #cloud-config
runcmd:
 - mkdir -pv /root/cloud-config-test
 - touch /root/cloud-config-test/boottest
 - echo "boot instance test" >> /root/cloud-config-test/boottest
    Note

    You must include the #cloud-config line at the top of the file.

  3. Boot an instance using the CLI, adding --user-data user-data.txt to the end of the boot command.

  4. When the instance has booted, log into the instance, switch to root and look in the directory. You will see the new file, and it will contain boot instance test.

This is a very simple example of what you can do with cloud-config, but you can see from this simple example that you can easily start to build fairly complicated setup scripts.

Next steps

You can find documentation for cloud-config at the following location:

https://cloudinit.readthedocs.io/en/latest/topics/examples.html

Feedback

If you find a problem with this article, click Improve this Doc to make the change yourself or raise an issue in GitHub. If you have an idea for how we could improve any of our services, send an email to feedback@ukcloud.com.