How to keep your Terraform code DRY by using Terramate (opens in new tab)

I feel like teams should be using tfe workspaces and env vars to instantiate environments rather than having a folder per-environment. It's pretty easy to replicate this workflow and results in substantially less env drift and code duplication when we do it.

I've been using Hiera (Puppet yaml data store) to source data for terraform. As a long time puppet user, when I started writing terraform code I really missed hiera. Turns out someone ported it to Go, and someone else turned that into a terraform provider. It's a game changer. No need for terragrunt or terramate. Hiera can return anything from a single value to a very complex data block that can be used to feed a module or a whole stack. Hiera needs some information about where you're deploying to, and it gets this in the in the provider configuration in the form of key/vals: I use environment, region & stack. I decided to use a workspace naming convention that encodes these (eg: prod_use1.network). For each workspace, terraform can automatically figure out exactly what lookups it needs to do, and hiera returns native terraform data relevant to that workspace only. I have 100% dry code, and no need to create a separate directory for each environment/region state. I run my terraform init/apply in the top-level directory no matter where I'm deploying. The result is that once I've written my modules and stacks, I can build out a whole data center by creating few workspaces and running "terraform init && terraform apply" in each one. Zero extra files or directories. Dry as a bone

I used to be obsessed with DRY. After having written tens of thousands of terraform lines in the last few years across a multitude of platforms and use cases, I say everything in moderation.

Going DRY is a decision you pay for in complexity, it's the typical programming problem of genericity. Sometimes it absolutely makes sense and you're a mad man if you skip it, but in isolated cases making things DRY just for the sake of it is just as nuts as not doing it when required.

It's a fine line to walk and it requires hands-on experience to know when to employ DRY and when to repeat yourself.