eaad725508
Add an easy to use helper function that is exposed to fetch a conductor in a way that matches how engines and persistence backends and jobboards are loaded. This also adjusts the single threaded conductor to be now named blocking conductor and exposes an entrypoint backend fetch() function to load current and future conductors. Change-Id: Id146d847c329d3e8510a8f24c3ec8b918680ddb5
82 lines
2.3 KiB
ReStructuredText
82 lines
2.3 KiB
ReStructuredText
----------
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Conductors
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----------
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Overview
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========
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Conductors in TaskFlow provide a mechanism that unifies the various TaskFlow
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concepts under a single easy to use (as plug-and-play as we can make it)
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construct.
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They are responsible for the following:
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* Interacting with :doc:`jobboards <jobs>` (examining and claiming
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:doc:`jobs <jobs>`).
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* Creating :doc:`engines <engines>` from the claimed jobs (using
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:ref:`factories <resumption factories>` to reconstruct the contained
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tasks and flows to be executed).
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* Dispatching the engine using the provided :doc:`persistence <persistence>`
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layer and engine configuration.
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* Completing or abandoning the claimed job (depending on dispatching and
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execution outcome).
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* *Rinse and repeat*.
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.. note::
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They are inspired by and have similar responsibilities
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as `railroad conductors`_.
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Considerations
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==============
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Some usage considerations should be used when using a conductor to make sure
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it's used in a safe and reliable manner. Eventually we hope to make these
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non-issues but for now they are worth mentioning.
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Endless cycling
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---------------
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**What:** Jobs that fail (due to some type of internal error) on one conductor
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will be abandoned by that conductor and then another conductor may experience
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those same errors and abandon it (and repeat). This will create a job
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abandonment cycle that will continue for as long as the job exists in an
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claimable state.
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**Example:**
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.. image:: img/conductor_cycle.png
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:scale: 70%
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:alt: Conductor cycling
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**Alleviate by:**
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#. Forcefully delete jobs that have been failing continuously after a given
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number of conductor attempts. This can be either done manually or
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automatically via scripts (or other associated monitoring).
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#. Resolve the internal error's cause (storage backend failure, other...).
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#. Help implement `jobboard garbage binning`_.
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.. _jobboard garbage binning: https://blueprints.launchpad.net/taskflow/+spec/jobboard-garbage-bin
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Interfaces
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==========
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.. automodule:: taskflow.conductors.base
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Implementations
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===============
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.. automodule:: taskflow.conductors.backends
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.. automodule:: taskflow.conductors.backends.impl_blocking
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Hierarchy
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=========
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.. inheritance-diagram::
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taskflow.conductors.base
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taskflow.conductors.backends.impl_blocking
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:parts: 1
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.. _railroad conductors: http://en.wikipedia.org/wiki/Conductor_%28transportation%29
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