NoCloud Metadata Server

A simple service for dynamically configuring Cloud-Init VMs using NoCloud, such as in edge compute environments and homelabs.

Config file structure

The server's configuration is loaded from a config.yaml file. It defaults to checking the current directory. Alternate paths can be specified using the --config=path/to/config.yaml flag.

The configuration is comprised of two main parts:

1. Server configs which defines basic information such as the regex patterns to trigger on, and the hostname to set.
2. User data templates, which define any number of user data modules to be provisioned.

A user data template may be referenced by multiple server configs via the userDataTemplate field. Each server config also has a replacements map that allows multiple similar server configs to reuse a single user data template, while customizing some fields by merging the map with the template.

Example

This example has a common base config which updates the system's packages on first boot, disables SSH password authentication, and then includes dev OR prod SSH keys depending on the requested URL.

userDataTemplates:
  basic:
    package_upgrade: true
    ssh_pwauth: false

serverConfigs:
- name: "basic-dev"
  matchPatterns:
  - "dev"
  instanceConfig:
    hostname: "basic-dev"
    enableInstanceIDSuffix: true
    enableHostnameSuffix: true
  userDataTemplate: "basic"
  replacements:
    ssh_authorized_keys:
    - ssh-rsa dev-management-ssh-key...

- name: "basic-prod"
  matchPatterns:
  - "prod"
  instanceConfig:
    hostname: "basic-prod"
    enableInstanceIDSuffix: true
    enableHostnameSuffix: true
  userDataTemplate: "basic"
  replacements:
    ssh_authorized_keys:
    - ssh-rsa prod-management-ssh-key...

$ curl localhost:8000/dev/meta-data
instance-id: i-dev-4a467d03
local-hostname: basic-dev-4a467d03
hostname: basic-dev-4a467d03

$ curl localhost:8000/dev/user-data
package_upgrade: true
ssh_authorized_keys:
  - ssh-rsa dev-management-ssh-key...
ssh_pwauth: false

$ curl localhost:8000/prod/meta-data
instance-id: i-prod-0138fed4
local-hostname: basic-prod-0138fed4
hostname: basic-prod-0138fed4

$ curl localhost:8000/prod/user-data
package_upgrade: true
ssh_authorized_keys:
  - ssh-rsa prod-management-ssh-key...
ssh_pwauth: false

Integration with QEMU/KVM

When creating QEMU VMs, you configure the SMBIOS serial such that Cloud-Init will retrieve the configuration from the metadata server after networking has been initialized.

Continuing the config example above, the options below would configure Cloud-Init to use the NoCloud data store, and to fetch the dev configuration from the metadata server running at 10.10.10.10:8000.

-smbios type=1,serial=ds=nocloud-net;s=http://10.10.10.10:8000/dev/

See the NoCloud docs and this helpful chart mapping DMI/SMBIOS options for more information on this subject.