SNS - Simple WorkFlow Service

Question 1

What is SWF?

Answer 1

Web service that makes it easy to coordinate work across distributed components.

Enables variety of use cases: media processing, business process workflows.

Coordinates tasks - steps in an application that can be done by human actions, code, scripts, etc.

Question 2

What are workers?

Answer 2

programs that interact with SWF to get tasks, process received tasks, return results

Question 3

What is the decider?

Answer 3

program that controls coordination of tasks: ordering, scheduling, etc. according to program logic

Question 4

Describe overview of workers and decider

Answer 4

Workers and deciders run on the cloud, or machines behind firewalls

SWF brokers interactions between workers and decider. Allows decider to get consistent views into progress of tasks and initiate new ones

SWF stores tasks, assigns them to workers.

SWF ensures tasks are assigned only once, never duplicated

SWF allows scaling since workers & deciders don’t have to track the execution state

Question 5

SWF vs SQS key differences

Answer 5

SWF - task only assigned once, never duplicated
SQS - task could be duplicated

SWF - task-oriented API
SQS - message oriented API

SWF process can last a year
SQS can last a few days

Question 6

What is the maximum workflow time?

Answer 6

Up to 1 year

Always measured in seconds

Question 7

Compare tracking in SWF and SQS

Answer 7

SWF tracks all tasks and events in application

SQS requires you to implement your own tracking