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Standalone mode

Warning

This mode is well-suited for development but not for production, since it uses the local machine alone to take decisions and process activity tasks.

In this mode, your local machine will act as:

  • workflow starter: it submits the workflow to Amazon SWF (via the StartWorkflowExecution endpoint)
  • decider: it polls SWF for decisions to take (via PollForDecisionTask) then takes decisions with the workflow class you passed and submit decisions to SWF (via RespondDecisionTaskCompleted)
  • activity worker: it polls SWF for activity tasks to execute (via PollForActivityTask) then processes the task and submit the result to SWF, either via RespondActivityTaskCompleted if successful, or via RespondActivityTaskFailed if not.

Usually you’ll want to tune the number of decider and worker processes that will be spawned by the command. The command will look like: 

simpleflow standalone --domain TestDomain \
    --nb-deciders 1 --nb-workers 1 \
    examples.basic.BasicWorkflow --input '[1]'

Your process tree will look like: 

/code/simpleflow# ps auxf|grep simpleflow
PID     COMMAND
  6 ... simpleflow standalone examples.basic.BasicWorkflow --input [1]
 10 ...  \_ simpleflow Decider(payload=DeciderPoller.start, nb_children=1)[running]
 12 ...  |   \_ simpleflow DeciderPoller(task_list=basic-1234)[processing]
 14 ...  |       \_ simpleflow DeciderPoller(task_list=basic-1234)[deciding]
 11 ...  \_ simpleflow Worker(payload=ActivityPoller.start, nb_children=1)[running]
 13 ...      \_ simpleflow ActivityPoller(task_list=basic-1234)[polling]

Under your command, you now see 2 subprocesses:

  • a Decider supervisor process, that forks to one or more DeciderPoller processes
  • a Worker supervisor process, that forks to one or more ActivityPoller processes

Each poller then forks when doing real work related to SWF. Here we’re in the middle of a decision for the workflow, and no activity task is running.