feat: Windows fast launch (#521)

Add an option for enabling [fast launch](https://docs.aws.amazon.com/AWSEC2/latest/WindowsGuide/win-ami-config-fast-launch.html) for Windows AMIs. This should speed up booting up of EC2 Windows runners.

Note that it does come with [extra cost](https://docs.aws.amazon.com/AWSEC2/latest/WindowsGuide/win-fast-launch-manage-costs.html).

```typescript
const ec2WindowsImageBuilder = Ec2RunnerProvider.imageBuilder(stack, 'Windows EC2 Builder', {
  os: Os.WINDOWS,
  vpc,
  awsImageBuilderOptions: {
    fastLaunchOptions: {
      enabled: true,
    },
  },
});
const runners = new GitHubRunners(stack, 'runners', {
  providers: [
    new Ec2RunnerProvider(stack, 'Fast Windows', {
      labels: ['windows'],
      imageBuilder: ec2WindowsImageBuilder,
    }),
  ],
}
```

Before:
<img width="69" alt="image" src="https://github.com/CloudSnorkel/cdk-github-runners/assets/1156773/f92a363e-9892-430a-9511-f70800909fe0">

After:
<img width="74" alt="image" src="https://github.com/CloudSnorkel/cdk-github-runners/assets/1156773/d7da163c-4f82-4cbb-9b48-bfb1e8da3850">

Resolves #466
Closes #514

src/image-builders/aws-image-builder/builder.ts

@@ -35,6 +35,48 @@ export interface AwsImageBuilderRunnerImageBuilderProps {
    * @default m5.large
    */
   readonly instanceType?: ec2.InstanceType;
+
+  /**
+   * Options for fast launch.
+   *
+   * This is only supported for Windows AMIs.
+   *
+   * @default disabled
+   */
+  readonly fastLaunchOptions?: FastLaunchOptions;
+}
+
+/**
+ * Options for fast launch.
+ */
+export interface FastLaunchOptions {
+  /**
+   * Enable fast launch for AMIs generated by this builder. It creates a snapshot of the root volume and uses it to launch new instances faster.
+   *
+   * This is only supported for Windows AMIs.
+   *
+   * @note this feature comes with additional resource costs. See the documentation for more details. https://docs.aws.amazon.com/AWSEC2/latest/WindowsGuide/win-fast-launch-manage-costs.html
+   * @note enabling fast launch on an existing builder will not enable it for existing AMIs. It will only affect new AMIs. If you want immediate effect, trigger a new image build. Alternatively, you can create a new builder with fast launch enabled and use it for new AMIs.
+   *
+   * @default false
+   */
+  readonly enabled?: boolean;
+
+  /**
+   * The maximum number of parallel instances that are launched for creating resources.
+   *
+   * Must be at least 6.
+   *
+   * @default 6
+   */
+  readonly maxParallelLaunches?: number;
+
+  /**
+   * The number of pre-provisioned snapshots to keep on hand for a fast-launch enabled Windows AMI.
+   *
+   * @default 1
+   */
+  readonly targetResourceCount?: number;
 }
 
 /**
@@ -266,6 +308,7 @@ export class AwsImageBuilderRunnerImageBuilder extends RunnerImageBuilderBase {
   private readonly instanceType: ec2.InstanceType;
   private infrastructure: imagebuilder.CfnInfrastructureConfiguration | undefined;
   private readonly role: iam.Role;
+  private readonly fastLaunchOptions?: FastLaunchOptions;
 
   constructor(scope: Construct, id: string, props?: RunnerImageBuilderProps) {
     super(scope, id, props);
@@ -285,6 +328,7 @@ export class AwsImageBuilderRunnerImageBuilder extends RunnerImageBuilderBase {
     this.baseImage = props?.baseDockerImage ?? defaultBaseDockerImage(this.os);
     this.baseAmi = props?.baseAmi ?? defaultBaseAmi(this, this.os, this.architecture);
     this.instanceType = props?.awsImageBuilderOptions?.instanceType ?? ec2.InstanceType.of(ec2.InstanceClass.M5, ec2.InstanceSize.LARGE);
+    this.fastLaunchOptions = props?.awsImageBuilderOptions?.fastLaunchOptions;
 
     // confirm instance type
     if (!this.architecture.instanceTypeMatch(this.instanceType)) {
@@ -587,6 +631,75 @@ export class AwsImageBuilderRunnerImageBuilder extends RunnerImageBuilderBase {
       requireImdsv2: true,
     });
 
+    const launchTemplateConfigs: imagebuilder.CfnDistributionConfiguration.LaunchTemplateConfigurationProperty[] = [{
+      launchTemplateId: launchTemplate.launchTemplateId,
+      setDefaultVersion: true,
+    }];
+    const fastLaunchConfigs: imagebuilder.CfnDistributionConfiguration.FastLaunchConfigurationProperty[] = [];
+
+    if (this.fastLaunchOptions?.enabled ?? false) {
+      if (!this.os.is(Os.WINDOWS)) {
+        throw new Error('Fast launch is only supported for Windows');
+      }
+
+      // create a separate launch template for fast launch so:
+      //  - settings don't affect the runners
+      //  - enabling fast launch on an existing builder works (without a new launch template, EC2 Image Builder will use the first version of the launch template, which doesn't have instance or VPC config)
+      //  - setting vpc + subnet on the main launch template will cause RunInstances to fail
+      //  - EC2 Image Builder seems to get confused with which launch template version to base any new version on, so a new template is always best
+      const fastLaunchTemplate = new ec2.CfnLaunchTemplate(this, 'Fast Launch Template', {
+        launchTemplateData: {
+          metadataOptions: {
+            httpTokens: 'required',
+          },
+          instanceType: this.instanceType.toString(),
+          networkInterfaces: [{
+            subnetId: this.vpc?.selectSubnets(this.subnetSelection).subnetIds[0],
+            deviceIndex: 0,
+            groups: this.securityGroups.map(sg => sg.securityGroupId),
+          }],
+          tagSpecifications: [
+            {
+              resourceType: 'instance',
+              tags: [{
+                key: 'Name',
+                value: `${this.node.path}/Fast Launch Instance`,
+              }],
+            },
+            {
+              resourceType: 'volume',
+              tags: [{
+                key: 'Name',
+                value: `${this.node.path}/Fast Launch Instance`,
+              }],
+            },
+          ],
+        },
+        tagSpecifications: [{
+          resourceType: 'launch-template',
+          tags: [{
+            key: 'Name',
+            value: `${this.node.path}/Fast Launch Template`,
+          }],
+        }],
+      });
+
+      launchTemplateConfigs.push({
+        launchTemplateId: fastLaunchTemplate.attrLaunchTemplateId,
+        setDefaultVersion: true,
+      });
+      fastLaunchConfigs.push({
+        enabled: true,
+        launchTemplate: {
+          launchTemplateId: fastLaunchTemplate.attrLaunchTemplateId,
+        },
+        maxParallelLaunches: this.fastLaunchOptions?.maxParallelLaunches ?? 6,
+        snapshotConfiguration: {
+          targetResourceCount: this.fastLaunchOptions?.targetResourceCount ?? 1,
+        },
+      });
+    }
+
     const stackName = cdk.Stack.of(this).stackName;
     const builderName = this.node.path;
 
@@ -608,11 +721,8 @@ export class AwsImageBuilderRunnerImageBuilder extends RunnerImageBuilderBase {
               'GitHubRunners:Builder': builderName,
             },
           },
-          launchTemplateConfigurations: [
-            {
-              launchTemplateId: launchTemplate.launchTemplateId,
-            },
-          ],
+          launchTemplateConfigurations: launchTemplateConfigs,
+          fastLaunchConfigurations: fastLaunchConfigs.length > 0 ? fastLaunchConfigs : undefined,
         },
       ],
     });

test/default.integ.snapshot/github-runners-test.assets.json

@@ -235,15 +235,15 @@
         }
       }
     },
-    "2aae55820f5b3b1bc6c23108a950d448c9f06303c2e15a71f6aed05080984ca5": {
+    "c778a1355556a7931c74bf18556e58cfff5dd5111b4157913931d869afcf4877": {
       "source": {
         "path": "github-runners-test.template.json",
         "packaging": "file"
       },
       "destinations": {
         "current_account-current_region": {
           "bucketName": "cdk-hnb659fds-assets-${AWS::AccountId}-${AWS::Region}",
-          "objectKey": "2aae55820f5b3b1bc6c23108a950d448c9f06303c2e15a71f6aed05080984ca5.json",
+          "objectKey": "c778a1355556a7931c74bf18556e58cfff5dd5111b4157913931d869afcf4877.json",
           "assumeRoleArn": "arn:${AWS::Partition}:iam::${AWS::AccountId}:role/cdk-hnb659fds-file-publishing-role-${AWS::AccountId}-${AWS::Region}"
         }
       }

test/default.integ.snapshot/github-runners-test.template.json

@@ -3405,7 +3405,8 @@
        {
         "LaunchTemplateId": {
          "Ref": "AMILinuxBuilderLaunchtemplateA29452C4"
-        }
+        },
+        "SetDefaultVersion": true
        }
       ],
       "Region": {
@@ -6416,7 +6417,8 @@
        {
         "LaunchTemplateId": {
          "Ref": "AMILinuxarm64BuilderLaunchtemplate8F5EFF44"
-        }
+        },
+        "SetDefaultVersion": true
        }
       ],
       "Region": {
@@ -7529,7 +7531,8 @@
        {
         "LaunchTemplateId": {
          "Ref": "WindowsEC2BuilderLaunchtemplate0A66E9C2"
-        }
+        },
+        "SetDefaultVersion": true
        }
       ],
       "Region": {