fix(stepfunctions-tasks): EMR Create Cluster does not support dynamic…

… allocation of step concurrency level (#18972)

Currently, it is not possible to set the `stepConcurrencyLevel` property dynamically as the validation in
place will step over it and indicate that the value specified at a JsonPath is invalid.

This fix adds a check to skip validation if the property contains an unresolved token

----

*By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license*

packages/@aws-cdk/aws-stepfunctions-tasks/lib/emr/emr-create-cluster.ts

@@ -206,7 +206,7 @@ export class EmrCreateCluster extends sfn.TaskStateBase {
       this.validateReleaseLabel(this.props.releaseLabel);
     }
 
-    if (this.props.stepConcurrencyLevel !== undefined) {
+    if (this.props.stepConcurrencyLevel !== undefined && !cdk.Token.isUnresolved(this.props.stepConcurrencyLevel)) {
       if (this.props.stepConcurrencyLevel < 1 || this.props.stepConcurrencyLevel > 256) {
         throw new Error(`Step concurrency level must be in range [1, 256], but got ${this.props.stepConcurrencyLevel}.`);
       }

packages/@aws-cdk/aws-stepfunctions-tasks/test/emr/emr-create-cluster.test.ts

@@ -202,6 +202,27 @@ describe('Cluster with StepConcurrencyLevel', () => {
     });
   });
 
+  test('can be set dynamically through JsonPath', async () => {
+    // WHEN
+    const task = new EmrCreateCluster(stack, 'Task', {
+      instances: {},
+      clusterRole,
+      name: 'Cluster',
+      serviceRole,
+      autoScalingRole,
+      stepConcurrencyLevel: sfn.JsonPath.numberAt('$.foo.bar'),
+      integrationPattern: sfn.IntegrationPattern.REQUEST_RESPONSE,
+    });
+
+    // THEN
+    expect(stack.resolve(task.toStateJson())).toMatchObject({
+      Parameters: {
+        'Name': 'Cluster',
+        'StepConcurrencyLevel.$': '$.foo.bar',
+      },
+    });
+  });
+
   test('throws if < 1 or > 256', async () => {
     expect(() => new EmrCreateCluster(stack, 'Task1', {
       instances: {},