CODEWITHSUNDEEP
amazon-web-servicesaws-cloudformation
user6932385
user6932385

Reputation: 31

Fn::Sub with a Mapping in a literal block to specify the user data script

Ok so reading the documentation on the The intrinsic function Fn::Sub. I can use a literal block to specify the user data script.

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}

and I can uses a mapping to substitute the ${Domain} variable with the resulting value from the Ref function.

Name: !Sub
    - www.${Domain}
    - { Domain: !Ref RootDomainName }

But what if I need to use a mapping substitute inside a literal block? Like for example:

"Fn::Base64": !Sub |
    <powershell>
        Write-host "My Domain is www.${Domain},{ Domain: !Ref RootDomainName }"
    </powershell>

This example does not work, and I haven't been unable to find a method that does. Any ideas? The first example makes userdata scripts much easier to write and looks cleaner, but without being able to to use !Ref or !Findinmap it's usefulness is reduced dramatically.

Anyone got any ideas?

Upvotes: 2

Views: 5151

Answers (2)

aBrav
aBrav

Reputation: 397

Since I arrived to this page through Google, and then found the solution through a different wording here(literally): How to use !FindInMap in !Sub | userdata section

I'll just add it to save some frustrated searching to others.

Essentially, you have to write your example using the 2nd syntax but a bit more verbosely:

Fn::Base64:
  Fn::Sub:
    - |+
      <powershell>
        Write-host "My Domain is www.${Domain}"
      </powershell>
    - Domain:
        Fn::Ref: RootDomainName

You may be able to shorten it a bit, but as the original poster said, mind your commas, quoting and usage of short forms.

P.S.: If the first solution has already served your purpose, you should mark it thus.

Upvotes: 6

Karel
Karel

Reputation: 179

In that case you would write it simply as ${RootDomainName}. Local resouces in the same stack can just be mapped by using their resource name.

Upvotes: 1

Related Questions