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333 lines
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ReStructuredText
333 lines
9.0 KiB
ReStructuredText
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.. _orchestrator-modules:
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.. py:currentmodule:: orchestrator
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ceph-mgr orchestrator modules
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=============================
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.. warning::
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This is developer documentation, describing Ceph internals that
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are only relevant to people writing ceph-mgr orchestrator modules.
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In this context, *orchestrator* refers to some external service that
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provides the ability to discover devices and create Ceph services. This
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includes external projects such as Rook.
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An *orchestrator module* is a ceph-mgr module (:ref:`mgr-module-dev`)
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which implements common management operations using a particular
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orchestrator.
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Orchestrator modules subclass the ``Orchestrator`` class: this class is
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an interface, it only provides method definitions to be implemented
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by subclasses. The purpose of defining this common interface
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for different orchestrators is to enable common UI code, such as
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the dashboard, to work with various different backends.
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.. graphviz::
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digraph G {
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subgraph cluster_1 {
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volumes [label="mgr/volumes"]
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rook [label="mgr/rook"]
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dashboard [label="mgr/dashboard"]
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orchestrator_cli [label="mgr/orchestrator"]
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orchestrator [label="Orchestrator Interface"]
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cephadm [label="mgr/cephadm"]
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label = "ceph-mgr";
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}
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volumes -> orchestrator
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dashboard -> orchestrator
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orchestrator_cli -> orchestrator
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orchestrator -> rook -> rook_io
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orchestrator -> cephadm
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rook_io [label="Rook"]
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rankdir="TB";
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}
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Behind all the abstraction, the purpose of orchestrator modules is simple:
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enable Ceph to do things like discover available hardware, create and
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destroy OSDs, and run MDS and RGW services.
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A tutorial is not included here: for full and concrete examples, see
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the existing implemented orchestrator modules in the Ceph source tree.
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Glossary
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--------
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Stateful service
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a daemon that uses local storage, such as OSD or mon.
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Stateless service
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a daemon that doesn't use any local storage, such
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as an MDS, RGW, nfs-ganesha, iSCSI gateway.
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Label
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arbitrary string tags that may be applied by administrators
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to hosts. Typically administrators use labels to indicate
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which hosts should run which kinds of service. Labels are
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advisory (from human input) and do not guarantee that hosts
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have particular physical capabilities.
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Drive group
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collection of block devices with common/shared OSD
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formatting (typically one or more SSDs acting as
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journals/dbs for a group of HDDs).
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Placement
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choice of which host is used to run a service.
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Key Concepts
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------------
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The underlying orchestrator remains the source of truth for information
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about whether a service is running, what is running where, which
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hosts are available, etc. Orchestrator modules should avoid taking
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any internal copies of this information, and read it directly from
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the orchestrator backend as much as possible.
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Bootstrapping hosts and adding them to the underlying orchestration
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system is outside the scope of Ceph's orchestrator interface. Ceph
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can only work on hosts when the orchestrator is already aware of them.
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Where possible, placement of stateless services should be left up to the
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orchestrator.
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Completions and batching
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------------------------
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All methods that read or modify the state of the system can potentially
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be long running. Therefore the module needs to schedule those operations.
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Each orchestrator module implements its own underlying mechanisms
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for completions. This might involve running the underlying operations
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in threads, or batching the operations up before later executing
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in one go in the background. If implementing such a batching pattern, the
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module would do no work on any operation until it appeared in a list
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of completions passed into *process*.
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Error Handling
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--------------
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The main goal of error handling within orchestrator modules is to provide debug information to
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assist users when dealing with deployment errors.
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.. autoclass:: OrchestratorError
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.. autoclass:: NoOrchestrator
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.. autoclass:: OrchestratorValidationError
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In detail, orchestrators need to explicitly deal with different kinds of errors:
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1. No orchestrator configured
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See :class:`NoOrchestrator`.
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2. An orchestrator doesn't implement a specific method.
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For example, an Orchestrator doesn't support ``add_host``.
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In this case, a ``NotImplementedError`` is raised.
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3. Missing features within implemented methods.
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E.g. optional parameters to a command that are not supported by the
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backend (e.g. the hosts field in :func:`Orchestrator.apply_mons` command with the rook backend).
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See :class:`OrchestratorValidationError`.
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4. Input validation errors
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The ``orchestrator`` module and other calling modules are supposed to
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provide meaningful error messages.
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See :class:`OrchestratorValidationError`.
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5. Errors when actually executing commands
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The resulting Completion should contain an error string that assists in understanding the
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problem. In addition, :func:`Completion.is_errored` is set to ``True``
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6. Invalid configuration in the orchestrator modules
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This can be tackled similar to 5.
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All other errors are unexpected orchestrator issues and thus should raise an exception that are then
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logged into the mgr log file. If there is a completion object at that point,
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:func:`Completion.result` may contain an error message.
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Excluded functionality
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----------------------
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- Ceph's orchestrator interface is not a general purpose framework for
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managing linux servers -- it is deliberately constrained to manage
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the Ceph cluster's services only.
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- Multipathed storage is not handled (multipathing is unnecessary for
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Ceph clusters). Each drive is assumed to be visible only on
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a single host.
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Host management
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---------------
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.. automethod:: Orchestrator.add_host
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.. automethod:: Orchestrator.remove_host
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.. automethod:: Orchestrator.get_hosts
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.. automethod:: Orchestrator.update_host_addr
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.. automethod:: Orchestrator.add_host_label
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.. automethod:: Orchestrator.remove_host_label
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.. autoclass:: HostSpec
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Devices
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-------
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.. automethod:: Orchestrator.get_inventory
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.. autoclass:: InventoryFilter
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.. py:currentmodule:: ceph.deployment.inventory
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.. autoclass:: Devices
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:members:
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.. autoclass:: Device
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:members:
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.. py:currentmodule:: orchestrator
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Placement
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---------
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A :ref:`orchestrator-cli-placement-spec` defines the placement of
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daemons of a specific service.
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In general, stateless services do not require any specific placement
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rules as they can run anywhere that sufficient system resources
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are available. However, some orchestrators may not include the
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functionality to choose a location in this way. Optionally, you can
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specify a location when creating a stateless service.
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.. py:currentmodule:: ceph.deployment.service_spec
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.. autoclass:: PlacementSpec
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:members:
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.. py:currentmodule:: orchestrator
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Services
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--------
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.. autoclass:: ServiceDescription
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.. py:currentmodule:: ceph.deployment.service_spec
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.. autoclass:: ServiceSpec
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:members:
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:private-members:
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:noindex:
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.. py:currentmodule:: orchestrator
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.. automethod:: Orchestrator.describe_service
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.. automethod:: Orchestrator.service_action
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.. automethod:: Orchestrator.remove_service
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Daemons
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-------
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.. automethod:: Orchestrator.list_daemons
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.. automethod:: Orchestrator.remove_daemons
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.. automethod:: Orchestrator.daemon_action
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.. autoclass:: DaemonDescription
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.. autoclass:: DaemonDescriptionStatus
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OSD management
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--------------
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.. automethod:: Orchestrator.create_osds
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.. automethod:: Orchestrator.blink_device_light
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.. autoclass:: DeviceLightLoc
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.. _orchestrator-osd-replace:
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OSD Replacement
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^^^^^^^^^^^^^^^
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See :ref:`rados-replacing-an-osd` for the underlying process.
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Replacing OSDs is fundamentally a two-staged process, as users need to
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physically replace drives. The orchestrator therefore exposes this two-staged process.
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Phase one is a call to :meth:`Orchestrator.remove_daemons` with ``destroy=True`` in order to mark
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the OSD as destroyed.
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Phase two is a call to :meth:`Orchestrator.create_osds` with a Drive Group with
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.. py:currentmodule:: ceph.deployment.drive_group
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:attr:`DriveGroupSpec.osd_id_claims` set to the destroyed OSD ids.
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.. py:currentmodule:: orchestrator
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Services
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--------
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.. automethod:: Orchestrator.add_daemon
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.. automethod:: Orchestrator.apply_mon
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.. automethod:: Orchestrator.apply_mgr
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.. automethod:: Orchestrator.apply_mds
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.. automethod:: Orchestrator.apply_rbd_mirror
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.. py:currentmodule:: ceph.deployment.service_spec
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.. autoclass:: RGWSpec
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:noindex:
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.. py:currentmodule:: orchestrator
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.. automethod:: Orchestrator.apply_rgw
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.. py:currentmodule:: ceph.deployment.service_spec
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.. autoclass:: NFSServiceSpec
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.. py:currentmodule:: orchestrator
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.. automethod:: Orchestrator.apply_nfs
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Upgrades
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--------
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.. automethod:: Orchestrator.upgrade_available
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.. automethod:: Orchestrator.upgrade_start
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.. automethod:: Orchestrator.upgrade_status
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.. autoclass:: UpgradeStatusSpec
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Utility
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-------
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.. automethod:: Orchestrator.available
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.. automethod:: Orchestrator.get_feature_set
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Client Modules
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--------------
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.. autoclass:: OrchestratorClientMixin
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:members:
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