Specs: Setting MAC for DPM NIC
Implements: blueprint neutron-integration-set-mac Change-Id: I4da0a674790e38253bbebb799f86c84723c10bd3
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Andreas Scheuring
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This work is licensed under a Creative Commons Attribution 3.0 Unported
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License.
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http://creativecommons.org/licenses/by/3.0/legalcode
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=============================================
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Neutron Integration - Setting the MAC address
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=============================================
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https://blueprints.launchpad.net/nova-dpm/+spec/neutron-integration-set-mac
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DPM does not support setting the MAC address for a NIC on its NIC creation.
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To workaround that, this blueprint proposes to set the MAC address from
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inside of the guest operating system.
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Problem Description
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===================
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DPM does not support setting the MAC address for a NIC on its NIC creation.
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It does also not offer a way to query the MAC address of an already created
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NIC. Therefore the MAC of the DPM NIC should be changed from within the
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operating system to ensure that the actual used MAC is equal the MAC of
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the Neutron port. That happens via a udev rule and a corresponding shell
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script.
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Use Cases
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---------
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* Attaching an instance to the network while using the correct MAC address
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* Assignment of IP addresses from the OpenStack DHCP
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* Using cloud-init to setup the networking with static ips (requires the MAC
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to be set correctly)
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Proposed Change
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===============
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Nova adds the relevant data to the 'boot-os-specific-parameters' property
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of an instance. This gets attached to the kernels cmdline during boot.
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The boot process itself ignores this data. Finally it's available in the
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guest operating system under `/proc/cmdline`.
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If a new qeth interface gets defined in the guest, a udev rule triggers
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a script which is able to read the relevant information from the
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cmdline and set the MAC for that interface accordingly. This also works for
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interfaces that are brought up during boot.
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.. note::
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Updating the 'boot-os-specific-parameters' property on a running partition
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will not be reflected in /proc/cmdline. This requires the partition to
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stopped and started again (A inband reboot is not sufficient).
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The format of the parameters is the following::
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<devno>,<port-no>,<mac>;
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Where
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* <devno> is the first device number, of the qeth device added, e.g. '0001'
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* <port-no> is the port number of the adapter, e.g. '0' or '1'
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* <mac> is the MAC address to be set, without the ':' delimiter,
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e.g. 'aabbccddeeff'
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The udev rule should call the script to configure the MAC for qeth devices
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only. As argument it passes in something that contains the interfaces device
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number.
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Due to the limitations of the 'boot-os-specific-parameters' property the
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maximum amount of Ports (NICs) per instance (partiton) is limited.
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* Max len of 'boot-os-specifc-parameters' = 256
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* len required per NIC = 20 (0001,1,aabbccddeeff;)
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* Max number of NICs = 256/20 = 12,8
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-> A single partition can not have more than 12 NICs.
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.. note::
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This number goes with the assumption that the 'boot-os-specific-parameters'
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property is used by this feature exclusively.
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Alternatives
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------------
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Using the ConfigDrive to provide the relevant information. This would add
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certain complexity to the scripts in the operating system. Those scripts would
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need to find and mount that ConfigDrive. A bunch of code would be required for
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that. In addition the ConfigDrive is not available in Ocata.
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Keeping the DPM chosen MAC and pushing this one back to Neutron.
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The problem with this approach is, that the Neutron port is created in the
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nova manager before any virt-driver gets invoked. Nova manager requests the
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port creation and binds it to the target host. Once the port is bound, changing
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the MAC is not possible anymore. That means, that the nova-dpm driver would
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need to unbind the port, change the MAC, bind it again.
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In addition there's no way to get the DPM chosen MAC address, as an
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appropriate attribute on the DPM NIC object does not exist.
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Data model impact
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-----------------
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None
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REST API impact
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---------------
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None
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Security impact
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---------------
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None
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Notifications impact
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--------------------
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None
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Other end user impact
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---------------------
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The max number of Ports (NICs) per Instance (partition) is limited to 12.
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Performance Impact
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------------------
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None
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Other deployer impact
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---------------------
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None
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Developer impact
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----------------
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None
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Implementation
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==============
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Assignee(s)
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-----------
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Primary assignee:
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<andreas-scheuring>
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Other contributors:
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None
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Work Items
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----------
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* All in one :)
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Dependencies
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============
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* Initial Neutron integration: https://blueprints.launchpad.net/nova-dpm/+spec/neutron-integration
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Testing
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=======
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* Unittest
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Documentation Impact
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====================
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Document the limitation of maximum 12 Ports per Instance.
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References
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==========
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* Nova ConfigDrive support: https://blueprints.launchpad.net/nova-dpm/+spec/config-drive
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