Mutable Generate

mutable-generate — Deduplicated generate block output

The mutable-generate experiment has been added. With it enabled, the contents a generate block produces are stored in the Content Addressable Store (CAS), and the file written at path is a read-only link to that stored copy rather than a file of its own.

Since the stored copy is addressed by the hash of its contents, anything generating identical contents links to the same copy. A generate block inherited by several hundred units therefore costs one copy in .terragrunt-cache rather than several hundred.

The link is read-only because that copy is shared. Where a generated file does need to be edited in place, a new mutable attribute on the generate block gives it a writable file of its own:

generate "provider" {
  path      = "provider.tf"
  if_exists = "overwrite"
  mutable   = true
  contents  = "..."
}

Setting mutable without the experiment enabled is an error, since earlier Terragrunt versions reject the attribute. The CAS is required, so --no-cas writes generated files directly and mutable has no effect.

For details, see the experiment documentation.