Build every environment from the same code

How to do it

Keep one module per layer and one small variables file per environment. Never write if environment == "production" to create a different kind of resource. When production needs a feature, such as a database replica, give staging the same feature at a smaller size. Run the same database engine and versions everywhere.

Example

# production.tfvars
environment       = "production"
instance_size     = "m7g.large"
instance_count    = 3
database_size     = "db.r7g.large"

# staging.tfvars: same resources, smaller
environment       = "staging"
instance_size     = "t4g.small"
instance_count    = 1
database_size     = "db.t4g.medium"

How to check

A diff between the staging and production folders shows only variables and backend settings. Both environments report the same module versions and engine versions.