Simple Workflow Service (SWS)

  1. AWS SWS is a cloud based web service that enables a sequence of tasks to be completed by a distributed set of programs/lambdas/EC2s/humans.
    1. A good example to Amazon’s own order taking/processing/fulfillment/shipping/returns system with a large number of tasks withing a single workflow.
    2. SWS is task oriented service (as opposed to SQS which is message oriented service)
  2. Three types of actors
    1. Starters initiate the workflow
    2. Workers are programs that can be run inside an EC2 or behind your firewall.
      1. retrieve tasks from SWS
      2. process the received tasks
      3. send results back to SWS
    3. A Decider program coordinates/orders/schedules task. They run inside an EC2 or behind your firewall.
      1. Also responsible for concurrency
  3. SWS responsibilities:
    1. SWS coordinates across workers/deciders.
    2. SWS stores tasks, assigns the tasks, monitors the tasks
    3. A task is assigned only once and never duplicated (unlike SQS messages)
    4. SWS maintains the state of the workflow
    5. The workers/deciders do not have to remember the application state hence workers/deciders can run and scale independently
  4. Workflows are grouped into domains. Domains isolate a set of tasks/executions/types from other domains within a given AWS account.
  5. A workflow can take upto a max 1 year to finish.
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