Kernel command line

In order to allow an ephemeral, or otherwise pristine image to receive some configuration, cloud-init will read a URL directed by the kernel command line and proceed as if its data had previously existed.

This allows for configuring a metadata service, or some other data.

Note

Usage of the kernel command line is somewhat of a last resort, as it requires knowing in advance the correct command line or modifying the boot loader to append data.

For example, when cloud-init init --local runs, it will check to see if cloud-config-url appears in key/value fashion in the kernel command line, as in:

root=/dev/sda ro cloud-config-url=http://foo.bar.zee/abcde

Cloud-init will then read the contents of the given URL. If the content starts with #cloud-config, it will store that data to the local filesystem in a static filename /etc/cloud/cloud.cfg.d/91_kernel_cmdline_url.cfg, and consider it as part of the config from that point forward.

If that file exists already, it will not be overwritten, and the cloud-config-url parameter is completely ignored.

Then, when the datasource runs, it will find that config already available.

So, to be able to configure the MAAS datasource by controlling the kernel command line from outside the image, you can append:

cloud-config-url=http://your.url.here/abcdefg

Then, have the following content at that url:

#cloud-config
datasource:
  MAAS:
    metadata_url: http://mass-host.localdomain/source
    consumer_key: Xh234sdkljf
    token_key: kjfhgb3n
    token_secret: 24uysdfx1w4

Warning

url kernel command line key is deprecated. Please use cloud-config-url parameter instead.

Note

Since cloud-config-url= is so generic, in order to avoid false positives, cloud-init requires the content to start with #cloud-config for it to be considered.

Note

The cloud-config-url= is un-authed http GET, and contains credentials. It could be set up to be randomly generated and also to check the source address in order to be more secure.