Templating CFN is really good practice once you hit a certain scale. If you have 5 DDB tables deployed to multiple regions, and on each of them you want to spec

Templating CFN is really good practice once you hit a certain scale. If you have 5 DDB tables deployed to multiple regions, and on each of them you want to specify keys, attributes, throughput, and usage alarms, at a minimum. That’s already 30-40 values that need to be specified, depending on table schemas. Add EC2, auto scaling, networking, load balancer, and SQS/SNS—now untemplated cloud formation is really unpleasant to work with. Some of the values like DDB table attributes are common across all regions, other values like tags are common across all infra in the same region. Some values are a scalar multiple of others, or interpolated from multiple sources. For example, a DDB capacity alarm for a given region is a conjunction of the table name (defined at the application level), a scalar multiple of the table capacity (defined at the regional deployment level), and severity (owned by those that will be on-call). To add insult to injury, a stack can only have 60 parameters, which you butt up against quickly if you try to naively parameterize your deployment. Given all these gripes, auto-generating CFN templates was easiest for me. I used a hierarchical config (global > application > region > resource) so the deployment params could be easily manipulated, maintained, and where “exceptions to the rule” would be obvious instead of hidden in a bunch of CFN yaml. To generate CFN templates I used ERB instead of jinja, but to similar effect. A side benefit of this is side-stepping additional vendor lock-in in the form of the weird and archaic CFN operators for math, string concatenation, etc. I don’t have a problem learning them, but it’s one of those things that one person learns, then everyone who comes after them has to re-learn. My shop already uses ruby, so templating in the same language is a no-brainer.