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This package handles meta and user data for different cloud and other platforms. It should be easy to extend to new platforms. Currently, it handles GCP metadata and a simple CDROM userdata provider. Signed-off-by: Rolf Neugebauer <rolf.neugebauer@docker.com>
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Metadata and Userdata handling
Most providers offer a mechanism to provide a OS with some additional
metadata as well as custom userdata. Metadata in this context is
fixed information provided by the provider (e.g. the host
name). Userdata is completely custom data which a user can supply to
the instance.
The metadata package handles both metadata and
userdata for a number of providers (see below). It abstracts over the
provider differences by exposing both metadata and userdata in a
directory hierarchy under /var/config. For example, sshd config
files from the metadata are placed under /var/config/ssh.
Userdata is assumed to be a single string and the contents will be
stored under /var/config/userdata. If userdata is a json file, the
contents will be further processed, where different keys cause
directories to be created and the directories are populated with files. Foer example, the following userdata file:
{
"ssh" : {
"sshd_config" : {
"perm" : "0600",
"content": "PermitRootLogin yes\nPasswordAuthentication no"
}
},
"foo" : {
"bar" : {
"perm": "0644",
"content": "foobar"
},
"baz" : {
"perm": "0600",
"content": "bar"
}
}
}
will generate the following files:
/var/config/ssh/sshd_config
/var/config/foo/bar
/var/config/foo/baz
This hierarchy can then be used by individual containers, who can bind mount the config sub-directory into their namespace where it is needed.
Providers
Below is a list of supported providers and notes on what is supported. We will add more over time.
GCP
GCP metadata is reached via a well known URL
(http://metadata.google.internal/) and currently
we extract the hostname and populate the
/var/config/ssh/authorized_keys from metadata. In the future we'll
add more complete SSH support.
GCP userdata is extracted from /computeMetadata/v1/instance/attributes/userdata.
HyperKit
HyperKit does not support metadata and userdata is passed in as a single file via a ISO9660 image.