How to get the CloudFormation resource value in user data bash code

Question

I tried to mount ec2 instance to efs in launch configuration which is written in the YAML CloudFormation. I don't know how to get File-system-id which is created in the CloudFormation template.

Is it possible to get the values of the AWS resource in bash code? Or is this any way that we can mount the ec2 instance to efs using CloudFormation.

LaunchConfig:
    Type: AWS::AutoScaling::LaunchConfiguration
    Properties:
      ImageId: ami-33f92051
      InstanceType: t2.micro
      AssociatePublicIpAddress: 'true'   #auto-assign public ip 
      KeyName: 
        Ref: KeyName
      SecurityGroups:
      - Ref: PublicEC2instancesSecurityGroupJing
      BlockDeviceMappings:
      - DeviceName: "/dev/xvda"
        Ebs:
          SnapshotId: 'snap-0821cc7c34fcb7b01'
          VolumeSize: 8
          DeleteOnTermination: 'false'
      UserData:
        Fn::Base64:
          Fn::Join:
          - "\n"
          - - "#!/bin/bash -xe"
            - sudo yum update -y
            - sudo yum -y install nfs-utils

            - file = 
            - Ref: EFSFileSystem
            - echo $file >> /var/www/html/index.html
            - cd /mnt
            - sudo mkdir efs
            - sudo mount -t nfs4 -o nfsvers=4.1,rsize=1048576,wsize=1048576,hard,timeo=600,retrans=2 $file.efs.ap-southeast-2.amazonaws.com:/ /mnt/efs

EFSFileSystem:
    Type: AWS::EFS::FileSystem
    Properties:
      PerformanceMode: generalPurpose
      ThroughputMode: bursting

John Hanley · Accepted Answer · 2018-10-09 05:04:21Z

1

To get the logical ID of the AWS::EFS::FileSystem:

!Ref EFSFileSystem

You can use it like this in your template:

        - sudo mkdir efs
        - !Join
            ''
              'sudo mount -t nfs4 -o nfsvers=4.1,rsize=1048576,wsize=1048576,hard,timeo=600,retrans=2 '
              !Ref 'EFSFileSystem'
              '.efs.ap-southeast-2.amazonaws.com:/'
              '/mnt/efs'

Make sure that you keep the spaces between the quotes correct so that the command line is built exactly like you need.

edited Oct 9, 2018 at 5:04

answered Oct 9, 2018 at 4:57

John Hanley

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2 Comments

Jing Zhang Over a year ago

But it says there is a format error in line 4 when I create the stack. Should I put '-' before each line?

Jing Zhang Over a year ago

Hi, I don't know why the folder efs is not created so I can't see if the mount is created.

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