AWS SWF Example

This app demonstrates how to use AWS Simple Workflow with the standard SDK. This is written in java, but since it uses the standard SDK it could easily be ported to C#.

This app runs a workflow that is trying to flip "heads" three times in a row. We have three activities (tasks) that are performed in this workflow.

• FlipCoinActivity : Flips either "HEADS" or "TAILS"
• HeadsActivity : Increments the headsCnt property
• TailsActivity : Sets the headsCnt property to zero

The workflow looks like this...

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Code Layout

I created a lightweight framework to handle some of the boilerplate of using the AWS SDK for SWF. These classes are under the "framework" directory.

The example workflow and activities are under the "workflow" directory.

The initial "main" entry to kick off the entire example is from the RunThreeHeadsWorkflow class. This class does the following...

• Registers the domain, workflow type and activity types with AWS. (This means manual configuration in AWS is not necessary)
• Starts the ActivityPoller to poll AWS for new activity tasks
• Starts the WorkflowPollers to poll AWS for new decision tasks
• Starts the workflow using the WorkflowStarter

The workflow class ThreeHeadsInARowWorkflow is what handles the decisions and schedules all the activities. This class is called from the WorkflowPoller ever time new decision tasks are available. This class does the following..

• Loops over history events in the decision tasks to populate a WorkflowState object
• Using the WorkflowState object decides what needs to be done next.
  • if an activity failed.. fail the workflow
  • if an activity times out.. fail the workflow
  • if we have a activity result (return value) figure out what activity needed to be called next - if we have 3 or more heads.. complete the workflow - if we have a heads... trigger HeadsActivity - if we have a tails... trigger TailsActivity - If we don't have heads or tails... trigger FlipCoinActivity
  • if workflow has been started and we don't have an activity result and no errors, trigger the first activity.

How to run it

Prerequisite

• java 7 or 8 (should work, tested on 1.8.0_74)

Setup

1. Clone this repo to your local machine and change directory to it.

   git clone [email protected]:NationalResearchCorporation/aws-swf-example.git

   cd aws-swf-example

2. Run gradle to build the project. From the root of the project run..

   gradlew.bat clean build copyDeps (windows)

   ./gradlew clean build copyDeps (mac/linux)

3. Copy the sample.system.properties and name it system.properties (keeping it in the project root directory). Edit the system.properties to use your aws access key and secret key

   cp sample.system.properties system.properties (mac/linux)

4. Run the app

   java -cp "build\libs\*" com.nationalresearch.aws.swf.example.RunThreeHeadsWorkflow (windows ?)

   java -cp "build/libs/*" com.nationalresearch.aws.swf.example.RunThreeHeadsWorkflow (mac/linux)

5. The app will trigger one workflow execution, but the pollers will not stop on their own own, to exit use Ctrl-C

Additional Info

The app registers everything under the test-domain, so if you login to AWS and look at the SWF console you should select this domain from the dropdown. You can see all the events and activities for any given workflow execution. You can even trigger a new workflow execution or re-run a failed or completed execution. If you have the app running (pollers are on) then when you trigger another execution from the AWS console you will see that the pollers pick up this new workflow execution.

The FlipCoin activity is setup to randomly throw an error, so occasionally you might see that the workflow execution failed and you'll see something like this...

ActivityPoller: ERROR: Executing activity : flip-coin-activity - Oh no! thumb got tired and couldn't flip the coin anymore.
ThreeHeadsInARowWorkflow: Activity failed.. Making call to SWF to fail this workflow

If the workflow execution completes you should see something like this...

ThreeHeadsInARowWorkflow: Workflow completed.. it took 5 flips and 10 activities to flip heads three times in a row... Sending complete workflow decision
ThreeHeadsInARowWorkflow:  -> Flip History -> [TAILS, TAILS, HEADS, HEADS, HEADS]