TaskFlow Y! + HP brownbag
Download as PPTX, PDF•2 likes•555 views
The document discusses TaskFlow, an OpenStack project that provides a framework for defining and executing workflows. It allows declarative definition of tasks and their dependencies. TaskFlow handles persistence of execution state, automatic migration of workflows between nodes, and horizontal scalability. It includes components like atoms, flows, engines, jobs, and conductors that together address challenges in distributed systems like resilience and high availability.
TaskFlow Y! + HP brownbag
- 2. ● Joshua Harlow ○ Yahoo! dev. for ~7 years ○ OpenStack dev. for ~3.5 years ○ Master Trouble-maker ○ Oslo, kazoo, anvil, taskflow, cloudinit… more … ● Min Pae ○ HP dev. for ~7 months ○ OpenStack dev. for ~7 months ○ Lead spell checker ○ Cue, taskflow, automaton… period ... Who are we
- 3. - Distributed systems are complex - Scale out, resumption, resilency, HA, visibility into active work … are not easily solveable problems (some learn this the hard way) - Understanding your states and workflows (and managing, transitioning and running) is key to solving many of these complex problems The problem
- 4. - Declarative workflows - Persisted execution state (checkpoints) - Automatic migration of workflows/jobs - Horizontal scalability - Magic! Taskflow does ...
- 5. - Atom (task and retry execution units) - Flow (composition unit) - Engine (work execution <-> persistence) - Job / Jobboard (work discovery/ownership unit) - Conductor (‘conducts’ automated discovery/ownership, flow construction and execution) Taskflow is ...
- 6. - Execution unit - Has - dependencies (“requires”) - data (“provides”) - Defines - execute(...) - business logic - revert(...) - exception handler Taskflow - Atom:Task class TakeABottleDown(task.Task): def execute(self, bottles_left): sys.stdout.write('Take one down, ') sys.stdout.flush() time.sleep(TAKE_DOWN_DELAY) return bottles_left - 1 def revert(self, **kwargs): … class PassItAround(task.Task): … class Conclusion(task.Task): ...
- 7. - Controls retry semantics of associated flow (and subflows and …) - Has - dependencies (“requires”) - data (“provides”) - Defines - execute(...) - business logic - revert(...) - exception handler - on_failure(...) - decision maker that affects retry semantics Taskflow - Atom:Retry class Retry1(retry.Retry): def execute(self, param1): print param1 return param1 + ‘ printed’ def revert(self, **kwargs) print “reverting...” def on_failure(self, **kwargs): if self.attempts < 5: return retry.RETRY else: return retry.REVERT_ALL
- 8. - Composition of Tasks - Defines transitions between Tasks - Allows implicit and explicit dependencies - Required methods(?) - add(...) - add (and link) task(s), flow(s) - iter_links(...) - iterator over the created links (links are created during add) Taskflow - Flow s = linear_flow.Flow(‘bottle-song’) take_bottle = TakeABottleDown(...) pass_it = PassItAround(...) next_bottles = Conclusion(...) s.add(take_bottle, pass_it, next_bottles)
- 9. - Run flows (and associated tasks) to completion - Decompose flows into a DAG - Edge dependencies mandated by flow(s) patterns are always retained - Prepare persistence layer - Run tasks/retries as they are ready - Optionally in parallel (and/or remotely)... - Save and fetch results from persistence layer and run next tasks/retries (and repeat) - State machine based: - http://docs.openstack.org/developer/taskflow/st ates.html#engine Taskflow - Engines(s)
- 10. - Place where work can be placed by producer entities and consumed/owned (and worked on) by other consumer entities - Similar to a job queue but builds in liveness semantics/capabilities (and semantics expect single ownership via a claim concept) - If a owner of a unit of work dies, the claim on the work they are performing is automatically lost and freed up for others - Typically tied to a unit of work (being a flow) and its optional persistence location (so that prior work can be resumed) Taskflow - Job(s) & Jobboard(s)
- 11. ● Essentially an advanced/specialized job processor - Connects to a jobboard - Periodically fetches contents of jobboard - Attempts to claim a job - Constructs jobs work (flow, other...) - Performs jobs work (using engines of various types and persistence backends to enable reliablility) - Removes job (on completion) - (rinse and repeat) ● Expected to be scaled out (run as many conductors as needed/desired) Taskflow - Conductor
- 12. Why would u want this?
- 13. - Jobs and Jobboards provide work ownership and work discovery - Horizontal scaling via conductors - Automatic migration of work between conductors - Persistence of execution state enable resumption and automated ownership transfer - When a conductor fails, job(s) in progress is picked up (and resumed to last checkpoint) by the next worker that frees up, no need to wait for the worker to come back. - Turn your software off safely and handle failures gracefully! Wherefore Taskflow?
- 14. - Declarative definition of work - Decouples what (Task, Flow) from how (Engine) - Coroutines are not separable from the surrounding code, and can not be automatically parallelized - Separation of declaration and execution allows flexibility in execution strategy - Engine tracks execution state and transitions - Parallel (green)threaded execution… - Remote worker execution… Wherefore Taskflow? (cont.)
- 15. - Not strongly tied into python as a language (for better or worse); concepts are easily transferable to java/go/…. - Alacarte: use what you want - Use the basics until you are ready to use jobboards, or select a local engine until you are ready to run remote workers… Wherefore Taskflow? (cont.)
- 17. Notifications Remote task workers Dynamic flow modification Real time dashboard of atom/flow/job transitions (WIP) Applications that can be paused DDOS your favorite site (joke) The potential is nearly limitless!! Wherefore Taskflow? (cont.)
- 18. DEMO
- 19. ?? Questions ??
- 20. - High level (overview) - https://wiki.openstack.org/wiki/TaskFlow - https://wiki.openstack.org/wiki/TaskFlow#Big_picture - Developer oriented (more detail) - http://docs.openstack.org/developer/taskflow/ - Extreme!! developer oriented (ultra detail) - Freenode - #openstack-state-management - #openstack-oslo - ML: [email protected] - Moar examples! More information!