cloud-init/doc/sources/azure

Azure Datasource

This datasource finds metadata and user-data from the Azure cloud platform.

Azure Platform

The azure cloud-platform provides initial data to an instance via an attached CD formated in UDF. That CD contains a 'ovf-env.xml' file that provides some information. Additional information is obtained via interaction with the "endpoint". The ip address of the endpoint is advertised to the instance inside of dhcp option 245. On ubuntu, that can be seen in /var/lib/dhcp/dhclient.eth0.leases as a colon delimited hex value (example: option unknown-245 64:41:60:82; is 100.65.96.130)

walinuxagent

In order to operate correctly, cloud-init needs walinuxagent to provide much of the interaction with azure. In addition to "provisioning" code, walinux does the following on the agent is a long running daemon that handles the following things: - generate a x509 certificate and send that to the endpoint

waagent.conf config

in order to use waagent.conf with cloud-init, the following settings are recommended. Other values can be changed or set to the defaults.

# disabling provisioning turns off all 'Provisioning.*' function
Provisioning.Enabled=n
# this is currently not handled by cloud-init, so let walinuxagent do it.
ResourceDisk.Format=y
ResourceDisk.MountPoint=/mnt

Userdata

Userdata is provided to cloud-init inside the ovf-env.xml file. Cloud-init expects that user-data will be provided as base64 encoded value inside the text child of a element named UserData or CustomData which is a direct child of the LinuxProvisioningConfigurationSet (a sibling to UserName) If both UserData and CustomData are provided behavior is undefined on which will be selected.

In the example below, user-data provided is 'this is my userdata', and the datasource config provided is {"agent_command": ["start", "walinuxagent"]}. That agent command will take affect as if it were specified in system config.

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>

Configuration

Configuration for the datasource can be read from the system config's or set via the 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.

The 'hostname_bounce: command' entry can be either the literal string 'builtin' or a command to execute. The command will be invoked after the hostname is set, and will have the 'interface' in its environment. If set_hostname is not true, then hostname_bounce will be ignored.

An example might be:

command: ["sh", "-c", "killall dhclient; dhclient $interface"]

datasource:
 agent_command
 Azure:
  agent_command: [service, walinuxagent, start]
  set_hostname: True
  hostname_bounce:
   # the name of the interface to bounce
   interface: eth0
   # policy can be 'on', 'off' or 'force'
   policy: on
   # the method 'bounce' command.
   command: "builtin"
   hostname_command: "hostname"
  }

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.

The interesting issue is that 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. Walinuxagent (in its current version) handles this by polling the state of hostname and bouncing ('ifdown eth0; ifup eth0' the network interface if it sees that a change has been made.

cloud-init handles this by setting the hostname in the DataSource's 'get_data' method via 'hostname $HostName', and then bouncing the interface. This behavior can be configured or disabled in the datasource config. See 'Configuration' above.