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Part 8: DAGMan

Learn about DAGMan, a workflow manager for Condor-G, that allows you to specify dependencies between your jobs and automatically manages them. Run simple and complex DAGMan jobs and recover failed ones.

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Part 8: DAGMan

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  1. Part 8:DAGMan

  2. Part 8: DAGMan • A: Grid Workflow Management • B: DAGMan • C: Laboratory: DAGMan

  3. A: Grid Workflow Management

  4. Job Dependencies • In many applications, some jobs are dependent on other jobs • E.g. job A must finish before job B starts • Often because job B uses output from job A • We call a set of interdependent jobs a workflow • Condor-G can run jobs in any order • We need a workflow manager

  5. Two Motivating Examples The Sloan Digital Sky Survey The Montage Project

  6. Sloan Digital Sky Survey • Map one-quarter of the entire sky • Determine the positions and absolute brightness of more than 100 million celestial objects. • Measure the distance to a million of the nearest galaxies, and to 100,000 quasars. http://www.sdss.org

  7. field brg cluster field catalog tsObj core brg core brg field tsObj brg field tsObj tsObj 2 1 4 1 1 3 2 2 2 1 5 3 Workflow to Find Galaxy Clusters getCatalog bcgCoal maxBcg maxBrg fieldPrep

  8. Workflow to Find Galaxy Clusters getCatalog bcgCoal maxBcg maxBrg

  9. Montage • Create a large mosaic image from many smaller images • Used for astronomy data • Correct optical distortions and intensity differences http://montage.ipac.caltech.edu

  10. Data Stage in nodes Montage compute nodes Data stage out nodes Inter pool transfer nodes Montage Workflow

  11. Montage Workflow 1202 nodes

  12. B: DAGMan

  13. DAGMan • Directed Acyclic Graph Manager • Workflow manager for Condor-G • DAGMan allows you to specify the dependencies between your Condor jobs, so it can manage them automatically for you. • By default, Condor may run your jobs in any order, or everything simultaneously, so we need DAGMan to enforce an ordering when necessary. • (e.g., “Don’t run job “B” until job “A” has completed successfully.”)

  14. Job A Job B Job C Job D What is a DAG? • A DAG is the datastructure used by DAGMan to represent these dependencies. • Each job is a “node” in the DAG. • Each node can have any number of “parent” or “children” nodes – as long as there are no loops!

  15. Job A Job B Job C Job D Defining a DAG • A DAG is defined by a .dagfile, listing each of its nodes and their dependencies: # diamond.dag Job A a.sub Job B b.sub Job C c.sub Job D d.sub Parent A Child B C Parent B C Child D • each node will run the Condor job specified by its accompanying Condor submit file

  16. Submitting a DAG • To start your DAG, just run condor_submit_dag with your .dag file, and Condor will start a personal DAGMan daemon which to begin running your jobs: % condor_submit_dag diamond.dag • condor_submit_dag submits a job with DAGMan as the executable. • This job happens to run on the submitting machine, not any other computer. • Thus the DAGMan daemon itself runs as a Condor job, so you don’t have to baby-sit it.

  17. Running a DAG • DAGMan acts as a “meta-scheduler”, managing the submission of your jobs to Condor based on the DAG dependencies. DAGMan A Condor Job Queue .dag File A B C D

  18. Running a DAG (cont’d) • DAGMan holds & submits jobs to the Condor queue at the appropriate times. DAGMan A Condor Job Queue B B C C D

  19. Running a DAG (cont’d) • In case of a job failure, DAGMan continues until it can no longer make progress, and then creates a “rescue” file with the current state of the DAG. DAGMan A Condor Job Queue Rescue File B X D

  20. Recovering a DAG • Once the failed job is ready to be re-run, the rescue file can be used to restore the prior state of the DAG. DAGMan A Condor Job Queue Rescue File B C C D

  21. Recovering a DAG (cont’d) • Once that job completes, DAGMan will continue the DAG as if the failure never happened. DAGMan A Condor Job Queue B C D D

  22. Finishing a DAG • Once the DAG is complete, the DAGMan job itself is finished, and exits. DAGMan A Condor Job Queue B C D

  23. Additional DAGMan Features • Provides other handy features for job management… • nodes can have PRE & POST scripts • failed nodes can be automatically re-tried a configurable number of times • job submission can be “throttled”

  24. Job A Job B Job C Job D Another sample DAGMan submit file # Filename: diamond.dag Job A A.condor Job B B.condor Job C C.condor Job D D.condor Script PRE A top_pre.csh Script PRE B mid_pre.perl $JOB Script POST B mid_post.perl $JOB $RETURN Script PRE C mid_pre.perl $JOB Script POST C mid_post.perl $JOB $RETURN Script PRE D bot_pre.csh PARENT A CHILD B C PARENT B C CHILD D Retry C 3

  25. Lab 8: DAGMan

  26. Lab 8: DAGMan • In this lab, you’ll: • Run a simple DAGMan job • Run a more complex DAGMan job • Recover a failed DAGMan job

  27. Credits • NSF disclaimer • Portions of this presentation were adapted from the following sources: • Jaime Frey, UW-Madison

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