feat: add support for Step Functions (#827)

Adds a construct library to model state machines in AWS Step Functions. Integrates with AWS Lambda to make it easy to build serverless workflows.

Author: rix0rrr

packages/@aws-cdk/aws-lambda/lib/lambda-ref.ts

@@ -5,6 +5,7 @@ import events = require('@aws-cdk/aws-events');
 import iam = require('@aws-cdk/aws-iam');
 import logs = require('@aws-cdk/aws-logs');
 import s3n = require('@aws-cdk/aws-s3-notifications');
+import stepfunctions = require('@aws-cdk/aws-stepfunctions');
 import cdk = require('@aws-cdk/cdk');
 import { cloudformation } from './lambda.generated';
 import { Permission } from './permission';
@@ -39,7 +40,7 @@ export interface FunctionRefProps {
 
 export abstract class FunctionRef extends cdk.Construct
   implements events.IEventRuleTarget, logs.ILogSubscriptionDestination, s3n.IBucketNotificationDestination,
-         ec2.IConnectable {
+         ec2.IConnectable, stepfunctions.IStepFunctionsTaskResource  {
 
   /**
    * Creates a Lambda function object which represents a function not defined
@@ -352,6 +353,19 @@ export abstract class FunctionRef extends cdk.Construct
     };
   }
 
+  public asStepFunctionsTaskResource(_callingTask: stepfunctions.Task): stepfunctions.StepFunctionsTaskResourceProps {
+    return {
+      resourceArn: this.functionArn,
+      metricPrefixSingular: 'LambdaFunction',
+      metricPrefixPlural: 'LambdaFunctions',
+      metricDimensions: { LambdaFunctionArn: this.functionArn },
+      policyStatements: [new iam.PolicyStatement()
+        .addResource(this.functionArn)
+        .addActions("lambda:InvokeFunction")
+      ]
+    };
+  }
+
   private parsePermissionPrincipal(principal?: iam.PolicyPrincipal) {
     if (!principal) {
       return undefined;

packages/@aws-cdk/aws-lambda/package.json

@@ -72,6 +72,7 @@
     "@aws-cdk/aws-s3": "^0.12.0",
     "@aws-cdk/aws-s3-notifications": "^0.12.0",
     "@aws-cdk/aws-sqs": "^0.12.0",
+    "@aws-cdk/aws-stepfunctions": "^0.12.0",
     "@aws-cdk/cdk": "^0.12.0",
     "@aws-cdk/cx-api": "^0.12.0"
   },