chore(aws-ec2): Fix code sample in docs for attaching volumes to EC2 (#…

…14376)

Fix for #14111
----

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packages/@aws-cdk/aws-ec2/README.md

@@ -962,8 +962,12 @@ const instance = new ec2.Instance(this, 'Instance', {
 volume.grantAttachVolumeByResourceTag(instance.grantPrincipal, [instance]);
 const targetDevice = '/dev/xvdz';
 instance.userData.addCommands(
+  // Retrieve token for accessing EC2 instance metadata (https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/instancedata-data-retrieval.html)
+  `TOKEN=$(curl -SsfX PUT "http://169.254.169.254/latest/api/token" -H "X-aws-ec2-metadata-token-ttl-seconds: 21600")`,
+  // Retrieve the instance Id of the current EC2 instance
+  `INSTANCE_ID=$(curl -SsfH "X-aws-ec2-metadata-token: $TOKEN" http://169.254.169.254/latest/meta-data/instance-id)`,
   // Attach the volume to /dev/xvdz
-  `aws --region ${Stack.of(this).region} ec2 attach-volume --volume-id ${volume.volumeId} --instance-id ${instance.instanceId} --device ${targetDevice}`,
+  `aws --region ${Stack.of(this).region} ec2 attach-volume --volume-id ${volume.volumeId} --instance-id $INSTANCE_ID --device ${targetDevice}`,
   // Wait until the volume has attached
   `while ! test -e ${targetDevice}; do sleep 1; done`
   // The volume will now be mounted. You may have to add additional code to format the volume if it has not been prepared.