Query related to Cloudformation with SSM

Question

Hi there,
I am trying to reference the following parameters in Cloudformation template under AWS::SSM::Association when trying to run commands.
* `aws ssm get-parameter --name /my-stack/my-parameter --query 'Parameter.Value' --output text --region !Ref MyRegion`
In above command I am not able to get the value of the region with ** !Ref MyRegion** which am passing as input parameter.
* `echo ${Instance1.PrivateIp} >> /home/ec2-user/ip.txt`.
Here also, I am not able to get the PrivateIp of the Instance1 Ec2.

This is what i am doing:-

```
RunCommandAssociation2:
    Type: 'AWS::SSM::Association'
    Properties:
      Name: 'AWS-RunShellScript'
      Targets:
        - Key: InstanceIds
          Values:
            - !Ref Instance2
      Parameters:
        commands:
          - echo $(curl http://169.254.169.254/latest/meta-data/local-ipv4) >> /home/ec2-user/ip.txt
          - value=$(aws ssm get-parameter --name /my-stack/my-parameter --query 'Parameter.Value' --output text --region '!Ref MyRegion')
          - echo "$value" >> /home/ec2-user/ip.txt
          - echo ${Instance1.PrivateIp} >> /home/ec2-user/ip.txt
```

Can anyone please help me here.
I want to pass these values in my SSM commands, just like we pass in user data.
Thanks in advance!

Answer

Hi,

As said in my answer to your initiai question, you must use Fn:Sub if you want to have ${Instance1.PrivateIp} properly substituted with its real value.

See examples on https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/intrinsic-function-reference-sub.html

The following is closest to your use case is this one if you replace UserData with your SSM doc

```
UserData:
  Fn::Base64:
    !Sub |
      #!/bin/bash -xe
      yum update -y aws-cfn-bootstrap
      /opt/aws/bin/cfn-init -v --stack ${AWS::StackName} --resource LaunchConfig --configsets wordpress_install --region ${AWS::Region}
      /opt/aws/bin/cfn-signal -e $? --stack ${AWS::StackName} --resource WebServerGroup --region ${AWS::Region}
```

If you don't use !Sub, you will remain with your variable name

Best,

Didier

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