feat(efs): support for new elastic throughputmode (aws#23200)

----

### All Submissions:

* [ yes] Have you followed the guidelines in our [Contributing guide?](https://github.com/aws/aws-cdk/blob/main/CONTRIBUTING.md)

### Adding new Construct Runtime Dependencies:

* [ ] This PR adds new construct runtime dependencies following the process described [here](https://github.com/aws/aws-cdk/blob/main/CONTRIBUTING.md/#adding-construct-runtime-dependencies)

### New Features

* [ ] Have you added the new feature to an [integration test](https://github.com/aws/aws-cdk/blob/main/INTEGRATION_TESTS.md)?
	* [ ] Did you use `yarn integ` to deploy the infrastructure and generate the snapshot (i.e. `yarn integ` without `--dry-run`)?

*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-efs/README.md

@@ -40,6 +40,8 @@ const fileSystem = new efs.FileSystem(this, 'MyEfsFileSystem', {
 });
 ```
 
+⚠️ An Amazon EFS file system's performance mode can't be MAX_IO when its throughputMode is ELASTIC.
+
 ⚠️ An Amazon EFS file system's performance mode can't be changed after the file system has been created.
 Updating this property will replace the file system.
 

packages/@aws-cdk/aws-efs/lib/efs-file-system.ts

@@ -13,6 +13,12 @@ import { CfnFileSystem, CfnMountTarget } from './efs.generated';
  * @see http://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/aws-resource-efs-filesystem.html#cfn-elasticfilesystem-filesystem-lifecyclepolicies
  */
 export enum LifecyclePolicy {
+
+  /**
+   * After 1 day of not being accessed.
+   */
+  AFTER_1_DAY = 'AFTER_1_DAY',
+
   /**
    * After 7 days of not being accessed.
    */
@@ -82,14 +88,19 @@ export enum PerformanceMode {
  */
 export enum ThroughputMode {
   /**
-   * This mode on Amazon EFS scales as the size of the file system in the standard storage class grows.
+   * This mode scales as the size of the file system in the standard storage class grows.
    */
   BURSTING = 'bursting',
 
   /**
    * This mode can instantly provision the throughput of the file system (in MiB/s) independent of the amount of data stored.
    */
-  PROVISIONED = 'provisioned'
+  PROVISIONED = 'provisioned',
+
+  /**
+  * This mode scales the throughput automatically regardless of file system size.
+  */
+  ELASTIC = 'elastic'
 }
 
 /**
@@ -333,6 +344,9 @@ export class FileSystem extends FileSystemBase {
       throw new Error('Property provisionedThroughputPerSecond is required when throughputMode is PROVISIONED');
     }
 
+    if (props.throughputMode === ThroughputMode.ELASTIC && props.performanceMode === PerformanceMode.MAX_IO) {
+      throw new Error('ThroughputMode ELASTIC is not supported for file systems with performanceMode MAX_IO');
+    }
     // we explictly use 'undefined' to represent 'false' to maintain backwards compatibility since
     // its considered an actual change in CloudFormations eyes, even though they have the same meaning.
     const encrypted = props.encrypted ?? (FeatureFlags.of(this).isEnabled(

packages/@aws-cdk/aws-efs/test/efs-file-system.test.ts

@@ -162,6 +162,29 @@ test('file system is created correctly with bursting throughput mode', () => {
   });
 });
 
+test('file system is created correctly with elastic throughput mode', () => {
+  // WHEN
+  new FileSystem(stack, 'EfsFileSystem', {
+    vpc,
+    throughputMode: ThroughputMode.ELASTIC,
+    performanceMode: PerformanceMode.GENERAL_PURPOSE,
+  });
+  // THEN
+  Template.fromStack(stack).hasResourceProperties('AWS::EFS::FileSystem', {
+    ThroughputMode: 'elastic',
+  });
+});
+
+test('Exception when throughput mode is set to ELASTIC, performance mode cannot be MaxIO', () => {
+  expect(() => {
+    new FileSystem(stack, 'EfsFileSystem', {
+      vpc,
+      throughputMode: ThroughputMode.ELASTIC,
+      performanceMode: PerformanceMode.MAX_IO,
+    });
+  }).toThrowError(/ThroughputMode ELASTIC is not supported for file systems with performanceMode MAX_IO/);
+});
+
 test('Exception when throughput mode is set to PROVISIONED, but provisioned throughput is not set', () => {
   expect(() => {
     new FileSystem(stack, 'EfsFileSystem', {