Fn::Sub expression does not resolve to a string - amazon-web-services

Question

I have created a parameter:
Parameters:
..
list:
Description: "Provide a list .."
Type: CommaDelimitedList
Default: "test1, test2"
Now I want to reference this list (which will resolve in "test1", "test2", ..) from a file in my cloudformation which looks like this:
configure_xx:
files:
/etc/file.conf:
content: !Sub |
input {
logs {
log_group => [ "${list}" ]
access_key_id => "${logstashUserKey}"
secret_access_key => "${logstashUserKey.SecretAccessKey}"
region => "eu-west-1"
}
}
How can I make this work for the parameter list? (the keys work).
error: Fn::Sub expression does not resolve to a string

Answer 1

Just switch the parameter type for a "String"
Parameters:
..
list:
Description: "Provide a list .."
Type: String
Default: "test1, test2"
If, for some reason, you have no control over this parameter type, you could use Fn::Join to transform the list to a string. For exemple:
configure_xx:
files:
/etc/file.conf:
content:
Fn::Sub:
- |-
input {
logs {
log_group => [ "${joinedlist}" ]
access_key_id => "${logstashUserKey}"
secret_access_key => "${logstashUserKey.SecretAccessKey}"
region => "eu-west-1"
}
}
- joinedlist:
Fn::Join:
- ', '
- !Ref list