Merge multiple CloudFormation template files into a single template. Each file may be in either JSON or YAML format.

Get started with template = MkStack::Template.new, or use the command line tool mkstack.

ERB¶ ↑

By default all files are run through an ERB (Embedded RuBy) processor.

<% desc = "awesome" %>

AWSTemplateFormatVersion: "2010-09-09"
Description: My <%= desc %> CloudFormation template

It is safe to leave this enabled. If a file doesn't have any ERB tags it is passed through untouched.

Include¶ ↑

MkStack searches each file for a section named Include, which should be a list of filenames. These function the same as adding the listed files on the command line.

JSON¶ ↑

"Include" : [
  "foo.yaml",
  "bar.json"
]

YAML¶ ↑

Include:
  - foo.yaml
  - bar.json

ERB and Include working together¶ ↑

MkStack uses a single binding for all files. This allows ERB tags defined in one file to be referenced in subsequent files.

foo.yaml¶ ↑

Include:
  - bar.json

<% tags_json = %q{
     "Tags": [
       { "Key" : "application", "Value" : "mkstack" }
     ]
   }
%>

bar.json¶ ↑

{
  "Resources" : {
    "sg": {
      "Type" : "AWS::EC2::SecurityGroup",
      "Properties" : {
        "GroupDescription" : {
             "Fn::Sub" : "Security Group for ${application}"
        }
        <%= tags_json %>
      }
    }
  }
}

Note that foo.yaml is processed before bar.json.

Command line tool¶ ↑

Usage: mkstack [ options ] file1 [ file2... ]
    -h, --help                       Display this message

    -d, --debug                      Show debug messages
    -v, --verbose                    Be verbose
    -q, --quiet                      Only show errors
    -s, --silent                     Don't show any log messages

    -o, --output=FILE                Print final template to FILE
                                     Use '-' for stdout
    -f, --format=FORMAT              Print as FORMAT
                                     Supported formats: json (default), yaml

        ‐‐erb, --[no-]erb            Perform ERB processing (default is true)
        ‐‐validate                   Call ValidateTemplate after merging

        ‐‐‐                          Marks end of mkstack options
                                     Remaining arguments are available to ERB as Array argv

Passing arguments to ERB¶ ↑

Any command line arguments following “—” are added to an Array called argv, which can be referenced in your ERB code.

foo.yaml¶ ↑

<% puts "#{argv.class} with #{argv.length} items: #{argv}" %>

¶ ↑

$ mkstack foo.yaml --- a 2 test
Array with 3 items: ["a", "2", "test"]