Reusable CloudFormation Snippets with ERB

Amazon’s CloudFormation is a wonderful and flexible tool for provisioning and managing resources in an EC2 VPC. It really takes the concept of infrastructure-as-code and helps make it a reality. For all its flexibility though, it sacrifices intuitiveness and ease. It is also limited by the rigidity of JSON, which isn’t a full-fledged language so it doesn’t support variables (although Parameters, Mappings, and References to them are a long-winded and difficult to parse approach that comes close) or easily referencing reusable external libraries. It also isn’t possible to define arbitrary functions, iterate over lists, or define anything but the most rudimentary conditional sections. This is by no means a criticism of CloudFormation, as it has certainly done a lot to turn a serialization format into a pseudo scripting language, but these are my observations that might frustrate other people when using it.

That’s where ERB comes in. As a big advocate of Ruby, whenever I think of templating the first thing that comes to mind is ERB. A while back, I put together a super simple script that generates templates from JSON “layouts” and “snippets” (think views and partials from Rails), both of which fully support ERB and all of its Ruby goodness.
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