UserData script with Resource Attribute CloudFormation

Question

The main question: How to I reference dependent resource attributes in a cloud formation template to build out a user data script.

What I have tried:

1. Approach listed here.
2. Examples from sub function

I am building a CloudFormation template for a three node Kafka cluster.

The approach I am taking here is configuring Zookeeper and Kafka on each node of the cluster using a UserData script on the EC2 instance.

I am using the Sub and Base64 functions to populate my user data script with the PrimaryPrivateIpAddress of my NetworkInterface but they are coming across as empty strings instead of the actual values. I know that the values are being populated correctly because they are part of my output in the template.

I have included the resource block of my template below as a reference. I omitted some uninteresting parts for the sake of succinctness. I also am illustrating a couple different approaches that I have tried to the EC2 resource blocks are not consistent.

EC2I8MWW:
  Type: 'AWS::EC2::Instance'
  DependsOn:
    - EC2NI2E8ES
    - EC2NI2PFST
    - EC2NI54B66
  Properties:
    KeyName: !Ref DesiredKeyName
    InstanceType: !Ref InstanceType
    NetworkInterfaces:
      - NetworkInterfaceId: !Ref EC2NI54B66
        DeviceIndex: "0"
    UserData:
      Fn::Base64:
        Fn::Sub:
          - |
            #!/bin/bash
            CONF="/etc/zookeeper/conf.dist/zoo.cfg"
            PRIVATE_1=${Private1}
            PRIVATE_2=${Private2}
            PRIVATE_3=${Private3}
            echo "# Zookeeper configuration for Talentreef" > "$CONF"
            cat <<EOT >> "$CONF"
            maxClientCnxns=50
            tickTime=2000
            initLimit=10
            syncLimit=5
            EOT
            echo "server.1=$PRIVATE_1:2888:3888" >> $CONF
            echo "server.2=$PRIVATE_2:2888:3888" >> $CONF
            echo "server.3=$PRIVATE_3:2888:3888" >> $CONF
            service zookeeper-server init --myid=$NODE_ID
            chkconfig zookeeper-server on
          - {
            Private1: !GetAtt EC2NI2E8ES.PrimaryPrivateIpAddress,
            Private2: !GetAtt EC2NI2PFST.PrimaryPrivateIpAddress,
            Private3: !GetAtt EC2NI54B66.PrimaryPrivateIpAddress
            }
EC2I2JVJI:
  Type: 'AWS::EC2::Instance'
  DependsOn: EC2NI54B66
  Properties:
    KeyName: !Ref DesiredKeyName
    InstanceType: !Ref InstanceType
    BlockDeviceMappings:
      - DeviceName: /dev/xvdb
        Ebs:
          VolumeType: st1
          DeleteOnTermination: 'true'
          VolumeSize: '500'
      - DeviceName: /dev/xvda
        Ebs:
          VolumeType: gp2
          DeleteOnTermination: 'true'
          VolumeSize: '8'
    ImageId: !FindInMap
      - AWSRegionArch2AMI
      - !Ref 'AWS::Region'
      - !FindInMap
        - AWSInstanceType2Arch
        - !Ref InstanceType
        - Arch
    NetworkInterfaces:
      - NetworkInterfaceId: !Ref EC2NI2PFST
        DeviceIndex: "0"
    UserData:
      Fn::Base64: !Sub |
        #!/bin/bash
        CONF="/etc/zookeeper/conf.dist/zoo.cfg"
        cp $CONF /etc/zookeeper/conf.dist/zoo.cfg.bak-$(date +%s)
        echo "# Zookeeper configuration for Talentreef" > "$CONF"
        cat <<EOT >> "$CONF"
        maxClientCnxns=50
        tickTime=2000
        initLimit=10
        syncLimit=5
        server.1=${EC2NI2E8ES.PrimaryPrivateIpAddress}:2888:3888
        server.2=${EC2NI2PFST.PrimaryPrivateIpAddress}:2888:3888
        server.3=${EC2NI54B66.PrimaryPrivateIpAddress}:2888:3888
        EOT
        service zookeeper-server init --myid=$NODE_ID
        chkconfig zookeeper-server on
        service zookeeper-server start
EC2I56LVQ:
  Type: 'AWS::EC2::Instance'
  DependsOn: EC2NI54B66
  Properties:
    KeyName: !Ref DesiredKeyName
    InstanceType: !Ref InstanceType
    BlockDeviceMappings:
      - DeviceName: /dev/xvdb
        Ebs:
          VolumeType: st1
          DeleteOnTermination: 'true'
          VolumeSize: '500'
      - DeviceName: /dev/xvda
        Ebs:
          VolumeType: gp2
          DeleteOnTermination: 'true'
          VolumeSize: '8'
    ImageId: !FindInMap
      - AWSRegionArch2AMI
      - !Ref 'AWS::Region'
      - !FindInMap
        - AWSInstanceType2Arch
        - !Ref InstanceType
        - Arch
    NetworkInterfaces:
      - NetworkInterfaceId: !Ref EC2NI2E8ES
        DeviceIndex: "0"
    UserData:
      Fn::Base64:
        Fn::Sub:
          - |
            CONF="/etc/zookeeper/conf.dist/zoo.cfg"
            cp $CONF /etc/zookeeper/conf.dist/zoo.cfg.bak-$(date +%s)
            echo "# Zookeeper configuration for Talentreef" > "$CONF"
            cat <<EOT >> "$CONF"
            maxClientCnxns=50
            tickTime=2000
            initLimit=10
            syncLimit=5
            EOT
            echo "server.1=${Private1}:2888:3888" >> $CONF
            echo "server.2=${Private2}:2888:3888" >> $CONF
            echo "server.3=${Private3}:2888:3888" >> $CONF
            service zookeeper-server init --myid=$NODE_ID
            chkconfig zookeeper-server on
          - {
            Private1: !GetAtt EC2NI2E8ES.PrimaryPrivateIpAddress,
            Private2: !GetAtt EC2NI2PFST.PrimaryPrivateIpAddress,
            Private3: !GetAtt EC2NI54B66.PrimaryPrivateIpAddress
            }
EC2NI54B66:
  Type: 'AWS::EC2::NetworkInterface'
  DependsOn: EC2NI2PFST
  Properties: {}
EC2NI2PFST:
  Type: 'AWS::EC2::NetworkInterface'
  DependsOn: EC2NI2E8ES
  Properties {}
EC2NI2E8ES:
  Type: 'AWS::EC2::NetworkInterface'
  Properties: {}

When this script runs I get the following output in the zoo.cfg file:

maxClientCnxns=50
tickTime=2000
initLimit=10
syncLimit=5
server.1=:2888:3888
server.2=:2888:3888
server.3=:2888:3888

Please let me know if I'm doing something wrong here or if I have to change my approach. Thank you for the help.

Answer 1

I think you're on the right path. I would just modify a bit the way you pass the 3 "private" substitute variables, for something like this (which I use quite often in my templates):

UserData:
  Fn::Base64:
    Fn::Sub:
      - |
        CONF="/etc/zookeeper/conf.dist/zoo.cfg"
        cp $CONF /etc/zookeeper/conf.dist/zoo.cfg.bak-$(date +%s)
        echo "# Zookeeper configuration for Talentreef" > "$CONF"
        cat <<EOT >> "$CONF"
        maxClientCnxns=50
        tickTime=2000
        initLimit=10
        syncLimit=5
        EOT
        echo "server.1=${Private1}:2888:3888" >> $CONF
        echo "server.2=${Private2}:2888:3888" >> $CONF
        echo "server.3=${Private3}:2888:3888" >> $CONF
        service zookeeper-server init --myid=$NODE_ID
        chkconfig zookeeper-server on
      - Private1: !GetAtt EC2NI2E8ES.PrimaryPrivateIpAddress
        Private2: !GetAtt EC2NI2PFST.PrimaryPrivateIpAddress
        Private3: !GetAtt EC2NI54B66.PrimaryPrivateIpAddress

So no brackets {} and no commas ,