What is a datasource?¶
Datasources are sources of configuration data for cloud-init that typically come from the user (aka userdata) or come from the stack that created the configuration drive (aka metadata). Typical userdata would include files, yaml, and shell scripts while typical metadata would include server name, instance id, display name and other cloud specific details. Since there are multiple ways to provide this data (each cloud solution seems to prefer its own way) internally a datasource abstract class was created to allow for a single way to access the different cloud systems methods to provide this data through the typical usage of subclasses.
Any metadata processed by cloud-init’s datasources is persisted as
/run/cloud-init/instance-data.json. Cloud-init provides tooling
to quickly introspect some of that data. See Instance Metadata for
The current interface that a datasource object must provide is the following:
# returns a mime multipart message that contains # all the various fully-expanded components that # were found from processing the raw userdata string # - when filtering only the mime messages targeting # this instance id will be returned (or messages with # no instance id) def get_userdata(self, apply_filter=False) # returns the raw userdata string (or none) def get_userdata_raw(self) # returns a integer (or none) which can be used to identify # this instance in a group of instances which are typically # created from a single command, thus allowing programmatic # filtering on this launch index (or other selective actions) @property def launch_index(self) # the data sources' config_obj is a cloud-config formatted # object that came to it from ways other than cloud-config # because cloud-config content would be handled elsewhere def get_config_obj(self) #returns a list of public ssh keys def get_public_ssh_keys(self) # translates a device 'short' name into the actual physical device # fully qualified name (or none if said physical device is not attached # or does not exist) def device_name_to_device(self, name) # gets the locale string this instance should be applying # which typically used to adjust the instances locale settings files def get_locale(self) @property def availability_zone(self) # gets the instance id that was assigned to this instance by the # cloud provider or when said instance id does not exist in the backing # metadata this will return 'iid-datasource' def get_instance_id(self) # gets the fully qualified domain name that this host should be using # when configuring network or hostname releated settings, typically # assigned either by the cloud provider or the user creating the vm def get_hostname(self, fqdn=False) def get_package_mirror_info(self)
Adding a new Datasource¶
The datasource objects have a few touch points with cloud-init. If you are interested in adding a new datasource for your cloud platform you’ll need to take care of the following items:
Identify a mechanism for positive identification of the platform: It is good practice for a cloud platform to positively identify itself to the guest. This allows the guest to make educated decisions based on the platform on which it is running. On the x86 and arm64 architectures, many clouds identify themselves through DMI data. For example, Oracle’s public cloud provides the string ‘OracleCloud.com’ in the DMI chassis-asset field.
cloud-init enabled images produce a log file with details about the platform. Reading through this log in
/run/cloud-init/ds-identify.logmay provide the information needed to uniquely identify the platform. If the log is not present, you can generate it by running from source
./tools/ds-identifyor the installed location
The mechanism used to identify the platform will be required for the ds-identify and datasource module sections below.
Add datasource module ``cloudinit/sources/DataSource<CloudPlatform>.py``: It is suggested that you start by copying one of the simpler datasources such as DataSourceHetzner.
Add tests for datasource module: Add a new file with some tests for the module to
cloudinit/sources/test_<yourplatform>.py. For example see
Update ds-identify: In systemd systems, ds-identify is used to detect which datasource should be enabled or if cloud-init should run at all. You’ll need to make changes to
Add tests for ds-identify: Add relevant tests in a new class to
tests/unittests/test_ds_identify.py. You can use
TestOracleas an example.
Add your datasource name to the builtin list of datasources: Add your datasource module name to the end of the
Add your your cloud platform to apport collection prompts: Update the list of cloud platforms in
cloudinit/apport.py. This list will be provided to the user who invokes
Enable datasource by default in ubuntu packaging branches: Ubuntu packaging branches contain a template file
debian/cloud-init.templatesthat ultimately sets the default datasource_list when installed via package. This file needs updating when the commit gets into a package.
Add documentation for your datasource: You should add a new file in
The following is a list of the implemented datasources. Follow for more information.
- Alibaba Cloud (AliYun)
- Alt Cloud
- Config Drive
- Digital Ocean
- Amazon EC2
- SmartOS Datasource
- Google Compute Engine