feat(neptune-alph): update README.md

Author: Dennis Ruhe

packages/@aws-cdk/aws-neptune-alpha/README.md

@@ -149,6 +149,31 @@ new neptune.DatabaseInstance(this, 'Instance', {
 });
 ```
 
+## Publicly accessible
+
+You can make instances publicly accessible by setting the `publiclyAccessible` property to `true` on the cluster.
+Note that iam authentication is required for this to be enabled:
+
+```ts
+new neptune.DatabaseCluster(this, 'Cluster', {
+    vpc,
+    instanceType: neptune.InstanceType.R5_LARGE,
+    publiclyAccessible: true,
+    iamAuthentication: true,
+});
+```
+
+Alternatively, you can also make individual instances publicly accessible, by setting the respective property on 
+the instance:
+
+```ts fixture=with-cluster
+new neptune.DatabaseInstance(this, 'Instance', {
+    cluster,
+    instanceType: neptune.InstanceType.R5_LARGE,
+    publiclyAccessible: true,
+});
+```
+
 ## Port
 
 By default, Neptune uses port `8182`. You can override the default port by specifying the `port` property:

packages/@aws-cdk/aws-neptune-alpha/lib/cluster.ts

@@ -404,6 +404,8 @@ export interface DatabaseClusterProps {
   /**
    * If set to true, the database instances in this cluster will be publicly accessible.
    *
+   * Note that iamAuthentication must be enabled.
+   *
    * @see DatabaseInstanceProps.publiclyAccessible
    * @see https://docs.aws.amazon.com/neptune/latest/userguide/neptune-public-endpoints.html
    *

packages/@aws-cdk/aws-neptune-alpha/lib/instance.ts

@@ -416,6 +416,8 @@ export interface DatabaseInstanceProps {
   /**
    * Indicates whether the DB instance is publicly accessible.
    *
+   * Note that iamAuthentication must be enabled on the cluster.
+   *
    * @default - false
    */
   readonly publiclyAccessible?: boolean;

packages/@aws-cdk/aws-neptune-alpha/test/integ.cluster.ts

@@ -43,7 +43,6 @@ const cluster = new DatabaseCluster(stack, 'Database', {
   kmsKey,
   removalPolicy: cdk.RemovalPolicy.DESTROY,
   autoMinorVersionUpgrade: true,
-  publiclyAccessible: true,
   cloudwatchLogsExports: [LogType.AUDIT],
   cloudwatchLogsRetention: logs.RetentionDays.ONE_MONTH,
 });

packages/@aws-cdk/aws-neptune-alpha/test/integ.instance-publicly-accessible.ts

@@ -14,7 +14,7 @@ import { ClusterParameterGroup, ParameterGroupFamily } from '../lib/parameter-gr
 
 const app = new cdk.App();
 
-const stack = new cdk.Stack(app, 'AutoMinorVersionUpgradeInstanceStack');
+const stack = new cdk.Stack(app, 'PubliclyAccessibleInstanceStack');
 
 const vpc = new ec2.Vpc(stack, 'VPC', { maxAzs: 2, natGateways: 1 });
 
@@ -32,6 +32,7 @@ const cluster = new DatabaseCluster(stack, 'Database', {
   instanceType: InstanceType.R5_LARGE,
   clusterParameterGroup,
   removalPolicy: cdk.RemovalPolicy.DESTROY,
+  iamAuthentication: true,
 });
 
 new DatabaseInstance(stack, 'EnabledInstance', {