Ability to pass user data as a parameter.

[mhussain]

Requesting the ability to pass user data as parameter to the stack instead of having to write in inline in the template.

Something like

DateInit: files/user_data.txt

"DataInit": {
  "Type": "String",
  "Description": "Initialisation script"
}
...

"UserData": { "Fn::Base64": { "Ref": "DataInit" } }

...

[simpsora]

👍 to this idea -- it would be nice to have UserData content extracted to a separate file.

For this to be most useful, the content of the would still need to be parsed by CloudFormation, in order to resolve intrinsic functions (Fn::Ref, Fn::GetAtt, etc.). Use of those functions may introduce some strange requirements when it comes to quoting the content.

[stevehodgkiss]

I saw an interesting solution to this in a sparkleformation issue: sparkleformation/sparkle_formation#54 (comment)

It enables separate user data files while being able to use ERB to call sparkle functions inside that file like <%= region! %>.

[simpsora]

@stevehodgkiss that's an interesting approach, although it's a shame that it only works with Sparkle. I'd love to see a more generic approach if possible (though I don't currently see how).

cloud-init has quite a bit more functionality than just user-data shell scripts, see here:
https://help.ubuntu.com/community/CloudInit

About the only idea I have is to create a grammar of some kind to allow embedding CF references/functions inline in the script, then replacing them with closequote-var-openquote:
...", { "Ref" : "Foo" }, "...

[simpsora]

@mhussain: 0.6.0 has been released, which contains user_data_file!. See #117 for details.

[stevehodgkiss]

I think the approach/code used in #117 could be used in JSON/YAML templates quite easily too, we'd just need to run it through the same Erubis context. It could look like this:

  "UserData": <%= user_data_file!('app.erb') %>