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 meta-data service, or some other data.
That 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
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, in order to be able to configure the MAAS DataSource by controlling the kernel command line from outside the image, you can append:
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
url kernel command line key is deprecated. Please use cloud-config-url parameter instead”
cloud-config-url= is so very generic, in order to avoid false
cloud-init requires the content to start with
#cloud-config in order
for it to be considered.
cloud-config-url= is un-authed http GET, and contains credentials.
It could be set up to be randomly generated and also check source
address in order to be more secure.