Spec: define state machines
Partially Implements: blueprint state-machine Change-Id: I3b5871c021f79a7e68934baeb0c5d04160e94def
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Hiroaki Kobayashi
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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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Define state machines
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=====================
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https://blueprints.launchpad.net/blazar/+spec/state-machine
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Define state machines for leases, reservations, and events, and use the status
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field of the leases table which is unused for now.
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Problem description
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===================
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Statuses of leases, reservations, and events cannot properly describe some
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actual statuses because state machines for leases, reservations, and events are
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not well defined for now. It causes inconsistency of statuses, unrecoverable
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failures and so on.
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Actually, currently leases have no status. Even though the leases table has a
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status field, it is not used. It should be used to describe the status of a
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lease properly.
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Use Cases
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---------
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* A lease owner can see the exact status of the lease in the lease parameters
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included in the request response.
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Proposed change
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===============
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Overview
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--------
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Define state machines of leases, reservations, and events as follows.
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Lease statuses
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^^^^^^^^^^^^^^
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Lease statuses are categorized into 2 types: stable or transitional.
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In the state machine shown below, stable statuses are drawn as black nodes
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while transitional statuses are drawn as gray nodes. Stable statuses change to
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transitional statuses when a specific method of the blazar manager is called.
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After the method has completed or failed, the transitional statuses change to
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stable statuses.
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A lease has the following four stable statuses:
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* **PENDING**: A lease has been successfully created and is ready to start.
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The lease stays in this status until it starts.
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* **ACTIVE**: A lease has been started and is active.
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* **TERMINATED**: A lease has been successfully terminated.
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* **ERROR**: Unrecoverable failures happened to the lease.
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Transitional statuses are as follows:
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* **CREATING**: A lease is being created.
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* **STARTING**: A lease is being started.
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* **UPDATING**: A lease is being updated.
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* **TERMINATING**: A lease is being terminated.
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* **DELETING**: A lease is being deleted. Any status can change to this status
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because delete is the highest prioritized operation. e.g. when a lease hangs
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up in the STARTING status, delete should be allowed.
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.. image:: ../../../images/lease_statuses.png
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:width: 600 px
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Reservation statuses
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^^^^^^^^^^^^^^^^^^^^
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A reservation has the following four statuses. Small letters are used for
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backward compatibility:
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* **pending**: A reservation has been successfully created and is ready to
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start. The reservation stays in this status until it starts.
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* **active**: A reservation has been started and is active.
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* **deleted**: Reserved resources have been successfully released.
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* **error**: Unrecoverable failures happened to resources.
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.. image:: ../../../images/reservation_statuses.png
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:width: 600 px
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Event statuses
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^^^^^^^^^^^^^^
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Event statuses are not changed.
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.. image:: ../../../images/event_statuses.png
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:width: 600 px
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Relationships between statuses
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^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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The following table shows conditions of statuses of reservations and events
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that have to be satisfied for each lease status.
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+-------------+-------------------+--------------------------+
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| Lease | Reservations | Events |
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+=============+===================+==========================+
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| CREATING | pending | start_lease: UNDONE |
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| | | , end_lease: UNDONE |
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+-------------+-------------------+--------------------------+
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| PENDING | pending | start_lease: UNDONE |
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| | | , end_lease: UNDONE |
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+-------------+-------------------+--------------------------+
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| STARTING | pending or active | start_lease: IN_PROGRESS |
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| | or error | , end_lease: UNDONE |
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+-------------+-------------------+--------------------------+
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| ACTIVE | active | start_lease: DONE |
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| | | , end_lease: UNDONE |
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+-------------+-------------------+--------------------------+
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| TERMINATING | active or deleted | start_lease: DONE |
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| | or error | , end_lease: IN_PROGRESS |
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+-------------+-------------------+--------------------------+
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| TERMINATED | deleted | start_lease: DONE |
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| | | , end_lease: DONE |
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+-------------+-------------------+--------------------------+
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| DELETING | Any status | Any status |
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+-------------+-------------------+--------------------------+
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| UPDATING | Any status | Any status other than |
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| | | IN_PROGRESS |
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+-------------+-------------------+--------------------------+
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Alternatives
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------------
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Express resource capacity sufficiency as a lease status like *_DEGRADED
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statuses and a reservation status like *_MISSING_RESOURCES and
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*_RESOURCES_CHANGED.
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The problem of this solution is that it complicates state machines.
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Instead, we will introduce boolean flags like *degraded* to leases and
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reservations for expressing such resource capacity sufficiency.
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See the resource-monitoring spec[1] in detail.
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Data model impact
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-----------------
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None
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RESTAPI 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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* Users can see the lease status.
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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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hiro-kobayashi
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Work Items
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----------
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* Implement LeaseStatus, ReservationStatus and EventStatus class that contain
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statuses and basic methods for managing these statuses.
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* Implement a decorator that checks/updates the lease status before/after
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*-lease methods of manager.
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* Decorate *-lease methods with the decorator.
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Dependencies
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============
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None
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Testing
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=======
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* Test status transitions.
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Documentation Impact
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====================
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None
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References
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==========
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* [1] resource-monitoring blueprint: https://blueprints.launchpad.net/blazar/+spec/resource-monitoring
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History
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=======
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.. list-table:: Revisions
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:header-rows: 1
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* - Release Name
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- Description
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* - Queens
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- Introduced
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Status graphs
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=============
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Status graphs are drawn by `draw.io`_ . To edit graphs, open `draw.io`_,
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select *Open Existing Diagram* and chose the *\*_statuses.xml* file under this
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directory.
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.. _draw.io: <https://www.draw.io/>
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