Serverless Step Functions: no more leaky abstractions

I have some exciting news to share with you about the Serverless Step Functions plugin.

One of the main pain points of using the plugin was that you needed to use fully-formed ARNs. We addressed this in v1.18.0 by supporting CloudFormation intrinsic functions Fn:GetAtt and Ref. This makes it possible for you to reference a local function instead.

functions: hello-world: handler: hello-world.handlerstepFunctions: stateMachines: myStateMachine: definition: StartAt: HelloWorld States: HelloWorld: Type: Task Resource: Fn::GetAtt: [HelloDashworldLambdaFunction, Arn] End: true

But this is still a leaky abstraction – you have to know how the Serverless framework converts local function names into CloudFormation logical IDs.

Newcomers would often get confused here.

“How did you get the logical ID HelloDashworldLambdaFunction from hello-world?”

I can hardly blame them for not knowing. This is an implementation detail in the Serverless framework, one that you shouldn’t have to care about!

Which is why I’m really happy to tell you that, as of v2.2.0 you can reference local functions using their local names in the state machine definition.

	functions:
	hello-world:
	handler: hello-world.handler
	stepFunctions:
	stateMachines:
	myStateMachine:
	definition:
	StartAt: firstTask
	States:
	firstTask:
	Type: Task
	Resource:
	Fn::GetAtt: [hello-world, Arn]
	Next: secondTask
	secondTask:
	Type: Task
	Resource: arn:aws:states:::lambda:invoke
	Parameters:
	FunctionName:
	# you can use Ref to get the function name
	Ref: hello-world
	Payload:
	answer: 42
	Next: thirdTask
	thirdTask:
	Type: Task
	Resource: arn:aws:states:::lambda:invoke.waitForTaskToken
	Parameters:
	FunctionName:
	# you can also use Fn::GetAtt to get the ARN
	Fn::GetAtt: [hello-world, Arn]
	Payload:
	token.$: $$.Task.Token
	End: true

view raw serverless.yml hosted with ❤ by GitHub

In the above example, when we reference the local function hello-world we no longer need to use its CloudFormation logical ID HelloDashworldLambdaFunction.

As you can see from the example, it applies when you use either Ref or Fn::GetAtt functions in a Task state. And it applies to all 3 ways of invoking a Lambda function from a Task state.

Hi, my name is Yan Cui. I’m an AWS Serverless Hero and the author of Production-Ready Serverless. I have run production workload at scale in AWS for nearly 10 years and I have been an architect or principal engineer with a variety of industries ranging from banking, e-commerce, sports streaming to mobile gaming. I currently work as an independent consultant focused on AWS and serverless.

You can contact me via Email, Twitter and LinkedIn.

Hire me.

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