36e20c3501
See the added doc/sources/azure/README.rst for why this is necessary. Essentially, we now are doing the following in the get_data() method of azure datasource to publish this NewHostname: hostname NewHostName ifdown eth0; ifup eth0
135 lines
5.1 KiB
ReStructuredText
135 lines
5.1 KiB
ReStructuredText
================
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Azure Datasource
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================
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This datasource finds metadata and user-data from the Azure cloud platform.
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Azure Platform
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--------------
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The azure cloud-platform provides initial data to an instance via an attached
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CD formated in UDF. That CD contains a 'ovf-env.xml' file that provides some
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information. Additional information is obtained via interaction with the
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"endpoint". The ip address of the endpoint is advertised to the instance
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inside of dhcp option 245. On ubuntu, that can be seen in
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/var/lib/dhcp/dhclient.eth0.leases as a colon delimited hex value (example:
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``option unknown-245 64:41:60:82;`` is 100.65.96.130)
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walinuxagent
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------------
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In order to operate correctly, cloud-init needs walinuxagent to provide much
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of the interaction with azure. In addition to "provisioning" code, walinux
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does the following on the agent is a long running daemon that handles the
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following things:
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- generate a x509 certificate and send that to the endpoint
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waagent.conf config
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~~~~~~~~~~~~~~~~~~~
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in order to use waagent.conf with cloud-init, the following settings are recommended. Other values can be changed or set to the defaults.
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::
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# disabling provisioning turns off all 'Provisioning.*' function
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Provisioning.Enabled=n
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# this is currently not handled by cloud-init, so let walinuxagent do it.
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ResourceDisk.Format=y
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ResourceDisk.MountPoint=/mnt
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Userdata
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--------
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Userdata is provided to cloud-init inside the ovf-env.xml file. Cloud-init
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expects that user-data will be provided as base64 encoded value inside the
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text child of a element named ``UserData`` or ``CustomData`` which is a direct
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child of the ``LinuxProvisioningConfigurationSet`` (a sibling to ``UserName``)
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If both ``UserData`` and ``CustomData`` are provided behavior is undefined on
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which will be selected.
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In the example below, user-data provided is 'this is my userdata', and the
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datasource config provided is ``{"agent_command": ["start", "walinuxagent"]}``.
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That agent command will take affect as if it were specified in system config.
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Example:
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.. code::
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<wa:ProvisioningSection>
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<wa:Version>1.0</wa:Version>
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<LinuxProvisioningConfigurationSet
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xmlns="http://schemas.microsoft.com/windowsazure"
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xmlns:i="http://www.w3.org/2001/XMLSchema-instance">
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<ConfigurationSetType>LinuxProvisioningConfiguration</ConfigurationSetType>
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<HostName>myHost</HostName>
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<UserName>myuser</UserName>
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<UserPassword/>
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<CustomData>dGhpcyBpcyBteSB1c2VyZGF0YQ===</CustomData>
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<dscfg>eyJhZ2VudF9jb21tYW5kIjogWyJzdGFydCIsICJ3YWxpbnV4YWdlbnQiXX0=</dscfg>
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<DisableSshPasswordAuthentication>true</DisableSshPasswordAuthentication>
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<SSH>
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<PublicKeys>
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<PublicKey>
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<Fingerprint>6BE7A7C3C8A8F4B123CCA5D0C2F1BE4CA7B63ED7</Fingerprint>
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<Path>this-value-unused</Path>
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</PublicKey>
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</PublicKeys>
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</SSH>
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</LinuxProvisioningConfigurationSet>
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</wa:ProvisioningSection>
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Configuration
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-------------
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Configuration for the datasource can be read from the system config's or set
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via the `dscfg` entry in the `LinuxProvisioningConfigurationSet`. Content in
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dscfg node is expected to be base64 encoded yaml content, and it will be
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merged into the 'datasource: Azure' entry.
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The '``hostname_bounce: command``' entry can be either the literal string
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'builtin' or a command to execute. The command will be invoked after the
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hostname is set, and will have the 'interface' in its environment. If
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``set_hostname`` is not true, then ``hostname_bounce`` will be ignored.
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An example might be:
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command: ["sh", "-c", "killall dhclient; dhclient $interface"]
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.. code::
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datasource:
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agent_command
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Azure:
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agent_command: [service, walinuxagent, start]
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set_hostname: True
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hostname_bounce:
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# the name of the interface to bounce
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interface: eth0
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# policy can be 'on', 'off' or 'force'
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policy: on
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# the method 'bounce' command.
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command: "builtin"
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hostname_command: "hostname"
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}
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hostname
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--------
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When the user launches an instance, they provide a hostname for that instance.
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The hostname is provided to the instance in the ovf-env.xml file as
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``HostName``.
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Whatever value the instance provides in its dhcp request will resolve in the
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domain returned in the 'search' request.
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The interesting issue is that a generic image will already have a hostname
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configured. The ubuntu cloud images have 'ubuntu' as the hostname of the
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system, and the initial dhcp request on eth0 is not guaranteed to occur after
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the datasource code has been run. So, on first boot, that initial value will
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be sent in the dhcp request and *that* value will resolve.
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In order to make the ``HostName`` provided in the ovf-env.xml resolve, a
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dhcp request must be made with the new value. Walinuxagent (in its current
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version) handles this by polling the state of hostname and bouncing ('``ifdown
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eth0; ifup eth0``' the network interface if it sees that a change has been
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made.
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cloud-init handles this by setting the hostname in the DataSource's 'get_data'
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method via '``hostname $HostName``', and then bouncing the interface. This
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behavior can be configured or disabled in the datasource config. See
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'Configuration' above.
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