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Merge pull request #1586 from errordeveloper/metadata-docs

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Few improvements to metadata docs
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Justin Cormack 2017-04-14 07:30:36 -05:00 committed by GitHub
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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.
Most providers offer two general mechanisms to provide compute instances
with information about the instance that cannot be discovered by any other
means. There are usually two types of information, namely _metadata_ and
_user-data_. Metadata is usually set by the provider (e.g. geographical
region of the datacentre, name given to the instance, external IP address,
tags and other similar information), while userdata is fully custom,
hence the name, and it is the information that user may supply to their
instances before launch (it is immutable in most providers).
The [metadata package](../pkg/metadata/) 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
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
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:
```
directories to be created and the directories are populated with files.
For example, the following userdata file:
```JSON
{
"ssh" : {
"sshd_config" : {
@ -66,5 +70,6 @@ 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.
HyperKit does not distiguish metadata and userdata, it's simply
refered to as data, which is passed to the VM as a disk image
in ISO9660 format.