[ops-guide] Add live migration content
Change-Id: I34d58d7ce2d48e24a79c5e56844aa8a1fc9e2b49 Implements: blueprint create-ops-guide
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Bjoern Teipel
Alexandra Settle
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=============================
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Nova instances live migration
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=============================
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Nova is capable of live migration instances from one host to
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a different host to support various operational tasks including:
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* Host Maintenance
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* Host capacity management
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* Resizing and moving instances to better hardware
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Nova configuration drive implication
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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Depending on the OpenStack-Ansible version in use, Nova can
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be configured to force configuration drive attachments to instances.
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In this case, a ISO9660 CD-ROM image will be made available to the
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instance via the ``/mnt`` mount point. This can be used by tools,
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such as cloud-init, to gain access to instance metadata. This is
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an alternative way of accessing the Nova EC2-style Metadata.
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To allow live migration of Nova instances, this forced provisioning
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of the config (CD-ROM) drive needs either be turned off, or the format of
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the configuration drive needs to be changed to a disk format like vfat, a
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format which both Linux and Windows instances can access.
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This work around is required for all Libvirt versions prior 1.2.17.
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To turn off the forced provisioning of the config drive, add the following
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override to the ``/etc/openstack_deploy/user_variables.yml`` file:
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.. code-block:: yaml
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nova_force_config_drive: False
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To change the format of the configuration drive, to a hard disk style format,
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use the following configuration inside the same
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``/etc/openstack_deploy/user_variables.yml`` file:
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.. code-block:: yaml
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nova_nova_conf_overrides:
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DEFAULT:
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config_drive_format: vfat
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force_config_drive: false
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Tunneling versus direct transport
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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In the default configuration, Nova determines the correct transport
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URL for how to transfer the data from one host to the other.
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Depending on the ``nova_virt_type`` override the following configurations
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are used:
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* kvm defaults to ``qemu+tcp://%s/system``
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* qemu defaults to ``qemu+tcp://%s/system``
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* xen defaults to ``xenmigr://%s/system``
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Libvirt TCP port to transfer the data to migrate.
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OpenStack-Ansible changes the default setting and used a encrypted SSH
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connection to transfer the instance data.
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.. code-block:: yaml
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live_migration_uri = "qemu+ssh://nova@%s/system?no_verify=1&keyfile={{ nova_system_home_folder }}/.ssh/id_rsa"
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Other configurations can be configured inside the
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``/etc/openstack_deploy/user_variables.yml`` file:
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.. code-block:: yaml
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nova_nova_conf_overrides:
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libvirt:
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live_migration_completion_timeout: 0
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live_migration_progress_timeout: 0
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live_migration_uri: "qemu+ssh://nova@%s/system?keyfile=/var/lib/nova/.ssh/id_rsa&no_verify=1"
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Local versus shared storage
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~~~~~~~~~~~~~~~~~~~~~~~~~~~
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By default, live migration assumes that your Nova instances are stored
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on shared storage and KVM/Libvirt only need to synchronize the
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memory and base image of the Nova instance to the new host.
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Live migrations on local storage will fail as a result of that assumption.
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Migrations with local storage can be accomplished by allowing instance disk
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migrations with the ``--block-migrate`` option.
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Additional Nova flavor features like ephemeral storage or swap have an
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impact on live migration performance and success.
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Cinder attached volumes also require a Libvirt version larger or equal to
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1.2.17.
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Executing the migration
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~~~~~~~~~~~~~~~~~~~~~~~
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The live migration is accessible via the nova client.
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.. code-block:: console
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nova live-migration [--block-migrate] [--force] <uuid> [<host>]
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Examplarery live migration on a local storage:
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.. code-block:: console
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nova live-migration --block-migrate <uuid of the instance> <nova host>
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Monitoring the status
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~~~~~~~~~~~~~~~~~~~~~
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Once the live migration request has been accepted, the status can be
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monitored with the nova client:
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.. code-block:: console
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nova migration-list
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+-----+------------+-----------+----------------+--------------+-----------+-----------+---------------+------------+------------+------------+------------+-----------------+
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| Id | Source Node | Dest Node | Source Compute | Dest Compute | Dest Host | Status | Instance UUID | Old Flavor | New Flavor | Created At | Updated At | Type |
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+----+-------------+-----------+----------------+--------------+-----------+-----------+---------------+------------+------------+------------+------------+-----------------+
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| 6 | - | - | compute01 | compute02 | - | preparing | f95ee17a-d09c | 7 | 7 | date | date | live-migration |
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+----+-------------+-----------+----------------+--------------+-----------+-----------+---------------+------------+------------+------------+------------+-----------------+
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To filter the list, the options ``--host`` or ``--status`` can be used:
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.. code-block:: console
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nova migration-list --status error
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In cases where the live migration fails, both the source and destination
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compute nodes need to be checked for errors. Usually it is sufficient
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to search for the instance UUID only to find errors related to the
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live migration.
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Other forms of instance migration
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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Besides the live migration, Nova offers the option to migrate entire hosts
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in a online (live) or offline (cold) migration.
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The following nova client commands are provided:
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* ``host-evacuate-live``
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Live migrate all instances of the specified host
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to other hosts if resource utilzation allows.
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It is best to use shared storage like Ceph or NFS
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for host evacuation.
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* ``host-servers-migrate``
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This command is similar to host evacuation but
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migrates all instances off the specified host while
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they are shutdown.
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* ``resize``
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Changes the flavor of an Nova instance (increase) while rebooting
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and also migrates (cold) the instance to a new host to accommodate
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the new resource requirements. This operation can take considerate
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amount of time, depending disk image sizes.
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