What is Terrascript

Terrascript is wrapper around Terraform which adds the ability to script repetitive tasks as inline ruby code.

Terrascript parses .tfrb files, executes ruby code and outputs .tf files.

Simply invoke tfsc with your usual Terraform arguments and enjoy the automation.

Usage

The overall structure is as shown below:

@inline
# ruby code
return
# plain text
@end

@inline directive marks the beginning of inline ruby code.

Code is evaluated until a return statement is found.

Text between return and @end statements is passed as an argument to the code. By default it's accessible inside the inline code under block variable, but you can override the name by specifying your own name in @inline directive.

For example @inline arg declaration will pass text in arg variable.

Anything the inline ruby code prints (puts) is written to the destination .tf file.

Examples

@inline
["one", "two"].each do |fn|
  puts block.gsub("<fn>", fn)
end
return
# <fn> alias
module "<fn>_alias" {
  source = "mewa/lambda-alias/aws"
  version = "1.0.0"

  alias = "${local.environment}"
  function_arn = "${aws_lambda_function.<fn>.arn}"
  function_name = "${aws_lambda_function.<fn>.function_name}"
  function_version = "${aws_lambda_function.<fn>.version}"
  invoke_arn = "${aws_lambda_function.<fn>.invoke_arn}"
}

# <fn> permission
resource "aws_lambda_permission" "<fn>_lambda_permission" {
  statement_id  = "AllowAPIGatewayInvoke"
  principal     = "apigateway.amazonaws.com"
  action        = "lambda:InvokeFunction"
  function_name = "${aws_lambda_function.<fn>.function_name}"
  qualifier = "${module.<fn>_alias.alias}"

  source_arn = "${aws_api_gateway_deployment.stage.execution_arn}/*/*"
}
@end

Will be rendered as

# one alias
module "one_alias" {
  source = "mewa/lambda-alias/aws"
  version = "1.0.0"

  alias = "${local.environment}"
  function_arn = "${aws_lambda_function.one.arn}"
  function_name = "${aws_lambda_function.one.function_name}"
  function_version = "${aws_lambda_function.one.version}"
  invoke_arn = "${aws_lambda_function.one.invoke_arn}"
}

# one permission
resource "aws_lambda_permission" "one_lambda_permission" {
  statement_id  = "AllowAPIGatewayInvoke"
  principal     = "apigateway.amazonaws.com"
  action        = "lambda:InvokeFunction"
  function_name = "${aws_lambda_function.one.function_name}"
  qualifier = "${module.one_alias.alias}"

  source_arn = "${aws_api_gateway_deployment.stage.execution_arn}/*/*"
}
# two alias
module "two_alias" {
  source = "mewa/lambda-alias/aws"
  version = "1.0.0"

  alias = "${local.environment}"
  function_arn = "${aws_lambda_function.two.arn}"
  function_name = "${aws_lambda_function.two.function_name}"
  function_version = "${aws_lambda_function.two.version}"
  invoke_arn = "${aws_lambda_function.two.invoke_arn}"
}

# two permission
resource "aws_lambda_permission" "two_lambda_permission" {
  statement_id  = "AllowAPIGatewayInvoke"
  principal     = "apigateway.amazonaws.com"
  action        = "lambda:InvokeFunction"
  function_name = "${aws_lambda_function.two.function_name}"
  qualifier = "${module.two_alias.alias}"

  source_arn = "${aws_api_gateway_deployment.stage.execution_arn}/*/*"
}

Future improvements

This project was written for my internal needs and serves its purpose.

However if it gains traction I could look into implementing a cleaner solution that abstracts the code for some common tasks and leaves open door for extension (plugins, probably).

The code presented here as an example could then look like this:

@replace "<fn>" with ["one", "two"]
# <fn> alias
module "<fn>_alias" {
    some_attribute = "${some_resource.<fn>.something}"
}
@end

terrascript

Development

What is Terrascript

Usage

Examples

Future improvements