Step Functions

step

with

Overview

Why would we use step functions?
How does that look in practice?
What mistakes I have made?
Are there rules you should follow?
What have I not tried yet?

About Me

Thomas Ankcorn
Senior Software Engineer at Baselime
Working with serverless and AWS for 4 years
@thomasankcorn on twitter
Forged at BAE Systems

who has used step functions?

why step functions?

Supportability Maintainability
Extendability
Observability

Perato Principle

The last 20% of the

work takes as long

as the first 80%

Use Step Functions where you make the money

How

Step function studio

Drag and drop is awesome
It helps you discover new possibilities
Exploring native integrations

DefinitionSubstitutions

SFN Workflow Sync

github.com/ljacobsson/sfn-workflow-studio-sync

Import into sls framework

functions:
   one: ...
   two: ...
resources:
  Resources:
    YourAwesomeStepFunction:
      Type: AWS::StepFunctions::StateMachine
        Properties: 
        Definition: ${file(./the-output-of-the-plugin.json)}
        DefinitionSubstitutions:
          One: !Ref OneLambdaFunction
          Two: !Ref TwoLambdaFunction
        RoleArn: !GetAtt SFNRole.Arn
    SFNRole:
    	Type AWS::Iam::Role
        Properties:
           ...YOU GOT THIS :D

Mistakes

Don't be a localhost hero

The mega lambda

Don't put all the code in one lambda

You don't need lambdas for everything

Rules

Start with a smoke test

test("Does my step function even work?", async () => {
	 const command = new StartExecutionCommand({
        input: JSON.stringify({ ... }),
        name: `test-invocation-${uuid()}`,
        stateMachineArn: arn
    });
    
    const result = await sfn.send(command);
    
    const execution = resolveWhenStatusComplete(response.executionArn);
    await expect(execution).toResolve()
})

Design for retries

From most common states

design your workflow so you can re-run it and get a good outcome

Each step should do only 1 thing

When using lambdas decompose your logic

Using nested step functions when it makes sense

Things I want to try

Custom UI

Step function API makes it possible to integrate workflow into your product

How possible is this in practice?

Build it with the CDK

const chain = Chain.start(openCase)
  .next(assignCase)
  .next(workOnCase)
  .next(
    isComplete
      .when(Condition.numberEquals('$.Status', 1), closeCase)
      .when(
      	Condition.numberEquals('$.Status', 0), 
        escalateCase.next(jobFailed)
       ),
  );