There's more...

To confirm that your EFS filesystem, mount targets, and security groups are working, you can also provision some client instances to connect to them. Add the following resources and parameters to the template you have already created:

1. Add the following parameters to your top-level Parameters section to configure your instances:

      MountPoint: 
        Description: The path on disk to mount the EFS file system 
        Type: String 
        Default: /mnt/efs 
      KeyName: 
        Description: The SSH key pair allowed to connect to the client 
          instance 
        Type: AWS::EC2::KeyPair::KeyName

2. Add an AutoScalingGroup under the Resources section; regardless of which AZ your servers are provisioned to, they will have access to the EFS filesystem via the local mount point:

      AutoScalingGroup: 
        Type: AWS::AutoScaling::AutoScalingGroup 
        DependsOn: MountTargetA 
        Properties: 
          MinSize: 2 
          MaxSize: 2 
          LaunchConfigurationName: 
            Ref: LaunchConfiguration 
          Tags: 
            - Key: Name 
              Value: 
                Fn::Sub: "${AWS::StackName} EFS Client" 
              PropagateAtLaunch: true 
          VPCZoneIdentifier: 
            Ref: SubnetIds

3. Still in the Resources section, add a launch configuration:

      LaunchConfiguration: 
        Type: AWS::AutoScaling::LaunchConfiguration 
        DependsOn: FileSystem 
        Properties: 
          ImageId: ami-1e299d7e 
        SecurityGroups: 
          - Ref: MountTargetAccessSecurityGroup 
        InstanceType: t2.micro 
        KeyName: 
          Ref: KeyName 
        UserData: 
          Fn::Base64: 
          Fn::Sub: |
            #!/bin/bash -xe
            mkdir -p ${MountPoint}
            echo 'Waiting for mount target DNS to propagate'
            sleep 90
            echo '${FileSystem}.efs.${AWS::Region}.amazonaws.com:/
            ${MountPoint} nfs4
            nfsvers=4.1,rsize=1048576,wsize=1048576,hard,timeo=600,
            retrans=2 0 0' >> 
            /etc/fstab
            mount -a\nchown ec2-user: ${MountPoint}\n"

4. Launch the CloudFormation stack with the following AWS CLI command, substituting your own parameter values:

      aws cloudformation create-stack \ 
        --stack-name wwns1 \
        --template-body file://03-working-with-network-storage.yaml \
        --parameters \
        ParameterKey=VpcId,ParameterValue=<vpc-id> \
        ParameterKey=SubnetIds,ParameterValue='<subnet-id-1>\, \
          <subnet-id-1>' \  
        ParameterKey=MountPoint,ParameterValue=<local-path-to-mount-efs> \
        ParameterKey=KeyName,ParameterValue=<existing-key-pair-name>

             Once the new stack is ready, you will be able to SSH to your instances and verify  
             that they have mounted the EFS filesystem.