Add support for user data files in sparkleformation templates

[stevehodgkiss]

Based on the code in this comment sparkleformation/sparkle_formation#54 (comment)

With this change, you can write the following in templates:

  user_data user_data_file!('web.erb', role: :web)

It will look in templates/user_data/* for user data files, read the template and compile it with each line being a separate string in the final array. The files can look like this and make use of SF helpers:

 #!/bin/bash

REGION=<%= region! %>
ROLE=<%= has_var?(:role) ? role : 'hmm' %>
echo $REGION

Renders like this:

+        "UserData": {
+          "Fn::Base64": {
+            "Fn::Join": [
+              "",
+              [
+                "#!/bin/bash\n",
+                "\n",
+                "REGION=",
+                {
+                  "Ref": "AWS::Region"
+                },
+                "ROLE=web",
+                "\n",
+                "echo $REGION\n"
+              ]
+            ]
+          }
+        }
+

Ref: #104

[taonic]

Not sure what this means.

[taonic]

Ok, I think I have a rough idea what this line does. But I wonder if this can be simplified a bit as the brackets could be redundant in the following evaluation, e.g.

src << " #{@bufvar} << #{code};"

[stevehodgkiss]

That breaks the test for custom vars, instead of returning the variables value it returns true.

       -"Fn::Base64" => {"Fn::Join"=>["", ["#!/bin/bash\n", "test_var", "\n", "yes", "\n"]]},
       +"Fn::Base64" => {"Fn::Join"=>["", ["#!/bin/bash\n", "test_var", "\n", true, "\n"]]},

[simpsora]

I'm pretty excited for this! I haven't tested it out yet (perhaps tomorrow), but it looks very promising.

👍 on green.

[patrobinson]

Should this be a separate Gem? I think this would be useful when using plain Sparkle without stack_master.

That being said, I like this approach. 👍

[taonic]

If we are monkey patching SparkleFormation::SparkleAttribute::Aws why can't we also monkey patch SparkleFormation::SparkleStruct. That way we don't have to define this TempalteContext just for erubis evaluation.

[stevehodgkiss]

Why would that be better? Variables require defining methods, so this throw away class means no side effects between multiple user data evaluations in the same template/process, if we patched SF then we'd need to clean those up so I prefer this approach instead.

[taonic]

Hum.. that actually make good sense.

[stevehodgkiss]

Made some updates, added custom vars. I think this is ready to be merged now.

@patrobinson yeah it could be a separate gem but it could also live in SparkleFormation itself. For now I'll leave it here.

[ejoubaud]

LGTM

[simpsora]

👍, I'm pretty happy with this. Nice job @stevehodgkiss!

Now let's get to work on command hooks and sync_master :-D

[taonic]

Belated 👍 Nice one!