Azure#
This datasource finds metadata and user data from the Azure cloud platform.
The Azure cloud platform provides initial data to an instance via an attached
CD formatted in UDF. This CD contains a ovf-env.xml
file that
provides some information. Additional information is obtained via interaction
with the “endpoint”.
IMDS#
Azure provides the instance metadata service (IMDS), which is a REST service
on 169.254.169.254
providing additional configuration information to the
instance. Cloud-init
uses the IMDS for:
Network configuration for the instance which is applied per boot.
A pre-provisioning gate which blocks instance configuration until Azure fabric is ready to provision.
Retrieving SSH public keys.
Cloud-init
will first try to utilise SSH keys returned from IMDS, and if they are not provided from IMDS then it will fall back to using the OVF file provided from the CD-ROM. There is a large performance benefit to using IMDS for SSH key retrieval, but in order to support environments where IMDS is not available then we must continue to all for keys from OVF[?]
Configuration#
The following configuration can be set for the datasource in system
configuration (in /etc/cloud/cloud.cfg
or
/etc/cloud/cloud.cfg.d/
).
The settings that may be configured are:
apply_network_config
Boolean set to True to use network configuration described by Azure’s IMDS endpoint instead of fallback network config of DHCP on eth0. Default is True.
apply_network_config_for_secondary_ips
Boolean to configure secondary IP address(es) for each NIC per IMDS configuration. Default is True.
data_dir
Path used to read metadata files and write crawled data.
disk_aliases
A dictionary defining which device paths should be interpreted as ephemeral images. See cc_disk_setup module for more info.
Configuration for the datasource can also be read from a dscfg
entry in
the LinuxProvisioningConfigurationSet
. Content in dscfg
node is
expected to be base64 encoded YAML content, and it will be merged into the
'datasource: Azure'
entry.
An example configuration with the default values is provided below:
datasource:
Azure:
apply_network_config: true
apply_network_config_for_secondary_ips: true
data_dir: /var/lib/waagent
disk_aliases:
ephemeral0: /dev/disk/cloud/azure_resource
User data#
User data is provided to cloud-init
inside the ovf-env.xml
file.
Cloud-init
expects that user data will be provided as a base64 encoded
value inside the text child of an element named UserData
or
CustomData
, which is a direct child of the
LinuxProvisioningConfigurationSet
(a sibling to UserName
).
If both UserData
and CustomData
are provided, the behaviour is
undefined on which will be selected. In the example below, user data provided
is 'this is my userdata'
.
Example:
<wa:ProvisioningSection>
<wa:Version>1.0</wa:Version>
<LinuxProvisioningConfigurationSet
xmlns="http://schemas.microsoft.com/windowsazure"
xmlns:i="http://www.w3.org/2001/XMLSchema-instance">
<ConfigurationSetType>LinuxProvisioningConfiguration</ConfigurationSetType>
<HostName>myHost</HostName>
<UserName>myuser</UserName>
<UserPassword/>
<CustomData>dGhpcyBpcyBteSB1c2VyZGF0YQ===</CustomData>
<dscfg>eyJhZ2VudF9jb21tYW5kIjogWyJzdGFydCIsICJ3YWxpbnV4YWdlbnQiXX0=</dscfg>
<DisableSshPasswordAuthentication>true</DisableSshPasswordAuthentication>
<SSH>
<PublicKeys>
<PublicKey>
<Fingerprint>6BE7A7C3C8A8F4B123CCA5D0C2F1BE4CA7B63ED7</Fingerprint>
<Path>this-value-unused</Path>
</PublicKey>
</PublicKeys>
</SSH>
</LinuxProvisioningConfigurationSet>
</wa:ProvisioningSection>
HostName#
When the user launches an instance, they provide a hostname for that instance.
The hostname is provided to the instance in the ovf-env.xml
file as
HostName
.
Whatever value the instance provides in its DHCP request will resolve in the domain returned in the ‘search’ request.
A generic image will already have a hostname configured. The Ubuntu cloud
images have ubuntu
as the hostname of the system, and the initial DHCP
request on eth0 is not guaranteed to occur after the datasource code has been
run. So, on first boot, that initial value will be sent in the DHCP request
and that value will resolve.
In order to make the HostName
provided in the ovf-env.xml
resolve, a DHCP request must be made with the new value. Cloud-init
handles this by setting the hostname in the datasource’s get_data
method
via hostname $HostName, and then bouncing the interface. This
behaviour can be configured or disabled in the datasource config. See
‘Configuration’ above.