cloud-init Tutorial — MyAdminDesk

This is an original planning guide. It is not a vendor manual, an official standard, or legal advice. Example addresses use documentation ranges. Review every command before you paste it.

What this hour is for

cloud-init runs on first boot. The generator drafts user-data. The validator checks that draft. Neither tool boots an instance. The instance is one you will administer.

Set the hostname, one user, and a key. The password is prompt-for-this and should not be in the file. Do not put a command that fetches a URL you do not administer. 192.0.2.10 is documentation. Do not hard-code it into production user-data.

A secret in user-data often lands in a log. Keep it out. Do not apply this to a live instance during the reading. 192.0.2.10/24 and example.com are documentation. They stay in the note.

The change you can finish

Apply nothing while you are writing the note. When the lab window opens, it is one change on the host named in the ticket. Read the draft, then the host, then decide.

Rollback is the file, the package version, or the snapshot you saved first. You do not invent a rollback after the only copy is gone.

Name the instance you will own.
Draft hostname, one user, and a key.
Remove passwords and documentation addresses.
Validate the YAML.
Reject a fetch of a URL you do not administer.
Do not boot it during the reading.

Mistakes that outlive the command

cloud-init Tutorial goes wrong in a small set of ways. The list is here so the ticket can forbid them before the window.

A password in the YAML.
A fetch of an arbitrary URL.
A documentation address in production user-data.
A secret that will land in a log.
Applied to a live instance during the reading.

Decisions to write down

One decision for cloud-init Tutorial: The instance will be yours. The user has a key. No password is in the file. No arbitrary URL is fetched. And nothing was booted yet.

Checks before you call it done

Confirm this before you call the change done: The hostname is written. The user is written. The validator was used. No password is present. And no instance was booted. If one of those fails, stop.

# Key, not a password in the YAML.
# Do not fetch a URL you do not administer.
# 192.0.2.10 is documentation.
# Do not boot during the reading.

Before you leave the host

cloud-init Tutorial ends when the hostname in the prompt matches the hostname in the ticket. If it does not, you are on the wrong host. Stop. A command that succeeded on the wrong host is not progress.

The draft stays a draft until a person has read the names in it. A generator does not log into the host and does not know which disk is empty. You delete a line that names a host, a path, or an account you did not write down.

192.0.2.10/24, gateway 192.0.2.1, 198.51.100.0/24, 203.0.113.0/24, and 2001:db8::/32 are documentation. example.com is a documentation name. They belong in the note. They are not values you leave on a host because a draft included them.

prompt-for-this is a reminder that a secret is missing. It is not a password, a key, or a token you save in the ticket or in git. The real secret stays in the password store.

One change is the window. If two things move and the result is wrong, you will not know which one did it. The next change waits for its own page.

If the same step fails twice, stop for the day. The failure is the result. Adding a forum command beside a half-applied change produces a host nobody can rebuild. Restore the copy you took first.

A second person reads the hostname and the change aloud. If they cannot find them in the ticket, the note is not done. Silence is not agreement. Then leave the host alone.

This page is a planning guide. It is not a vendor manual, not an official standard, and not permission to touch a host you do not administer. You do not disable a firewall, AppArmor, or SELinux to make a check pass.

Tools for this guide

These tools run in the browser on this site. They do not log into your machines.

Server Provisioning Guide

More in this cluster

The pillar for this page, and the next published pages filed with it.

Companion: Cloud: Terraform Basics.