July 29, 2014

Luigi

The past, the present, the future

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The history2

The long story builder (2009-2010)XML madness Only used for one single project (my Master’s thesis)

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The long story builder2 (2010-2011)Everything in Python, but insane amounts of boiler plate

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Why luigi?

We wanted to do everything in Python, not XML

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How do we use it at Spotify?

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Blah

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The things we got right

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Everything is a directed acyclic graph

Makefile style Tasks specify what they are dependent on not what other things depend on them

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Do everything in Python

Dependencies often involve algebra hard to express in XML

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Centralized scheduler

Overview of everything that’s currently running/scheduled

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Luigi worker 1 Luigi worker 2

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Luigi central planner

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Trigger jobs locally is trivial

If the only way is to run things remotely, debugging is super hard Running things locally makes it a lot easier No messing around with paths and configuration !(this has a flip side – more on this later)

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It’s a library more than a framework

Avoid the “Hollywood principle” and make it easy to customize etc

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The hairy parts…

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Execution is tied to scheduling

You can’t run this task “in the cloud” and go away

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Visualization is pretty rudimentary

See how nice Driven looks for instance: !

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Scheduling isn’t tied to triggering

Need to rely on crontab etc Could borrow some of the nice parts of Chronos:

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What are some ideas for the future?

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Separate scheduling and execution

Schedule something to run later/somewhere else !Recent baby step towards this is a very simple fix for running modules dynamically: !$ luigi --module MyModule MyTask --foo xyz --bar 123!!The next step would be to do something like !$ luigi --module MyModule MyTask --foo xyz --bar 123 --execute-remotely !!A full implementation would include a bunch of command line options to probe status, kill tasks, etc

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Separate scheduling and execution (2)

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Luigi central scheduler

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On-the-fly dependencies

class MyTask(luigi.Task):! def run(self):! input = yield OtherTask() # this could replace requires()

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Built in crontab-replacement

@luigi.schedule!class MyTask(luigi.Task):! param = luigi.DateParameter(default=datetime.date.today())! def run(self):! …!!The @luigi.schedule decorator would then 1. Register that my_module.MyTask should be scheduled (by telling the central planner?) 2. Trigger it continuously from somewhere (central planner?)

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ETA for tasks

Using a persistent task history database, you could train a simple k-NN classifier to predict how long a task will run

Then use this with the dependency graph to predict when any task will finish

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More features in the central planner

Kill a task Re-launch a task Launch a new task

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Support for other languages

Luigi is written in Python – but the RPC is language agnostic.

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Happy plumbing!

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Questions?

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