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66 lines
2.1 KiB
ReStructuredText
66 lines
2.1 KiB
ReStructuredText
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Architecture
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------------
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.. figure:: http://i.imgur.com/wTIeg2T.png
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:alt: Django Q schema
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Signed Tasks
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""""""""""""
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Tasks are first pickled and then signed using Django's own
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signing module before being sent to a Redis list. This ensures that task
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packages on the Redis server can only be executed and read by clusters
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and django servers who share the same secret key.
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Optionally the packages can be compressed before transport
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Pusher
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""""""
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The pusher process continuously checks the Redis list for new task
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packages and pushes them on the Task Queue.
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Worker
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""""""
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A worker process checks the package signing, unpacks the task, executes
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it and saves the return value. Irrespective of the failure or success of
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any of these steps, the package is then pushed onto the Result Queue.
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Monitor
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"""""""
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The result monitor checks the Result Queue for processed packages and
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saves both failed and successful packages to the Django database.
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Sentinel
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""""""""
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The sentinel spawns all process and then checks the health of all
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workers, including the pusher and the monitor. Reincarnating processes
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if any may fail. In case of a stop signal, the sentinel will halt the
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pusher and instruct the workers and monitor to finish the remaining
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items , before exiting. see Stop procedure
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Timeouts
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""""""""
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Before each task execution the worker resets a timer on the sentinel and resets it again after execution.
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Meanwhile the the sentinel checks if the timers don't exceed the timeout amount, in which case it will terminate the worker and reincarnate a new one.
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Hooks
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"""""
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Packages can be assigned a hook function, upon completion of the package
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this function will be called with the Task object as the first argument.
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Stop procedure
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""""""""""""""
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When a stop signal is given, the sentinel exits the guard loop and instructs the pusher to stop pushing.
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Once this is confirmed, the sentinel pushes poison pills onto the task queue and will wait for all the workers to die.
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This ensure that the task is emptied before the workers exit. Afterwards the sentinel waits for the monitor to empty the result queue before the stop flow is complete.
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