Terragrunt remote_state backend generation errors in CI

A remote_state block tells Terragrunt to generate the backend configuration for each module. It fails when a module already declares its own backend block, or when the generated file collides with a committed one, producing a duplicate or overwrite error.

What this error means

terragrunt init fails with "Backend configuration changed" or Terraform reports two backend blocks, because remote_state generated a backend.tf that conflicts with a committed one.

Error: Duplicate backend configuration

  on backend.tf line 1:
   1: terraform { backend "s3" { ... } }
A module may have only one backend configuration block, but remote_state also generated one.

Common causes

The module already has a hand-written backend block

remote_state generates backend.tf, but the module source also declares a backend block, so Terraform sees two.

The generate settings do not allow safe overwrite

A stale committed backend file blocks the generated one because if_exists is not set to overwrite Terragrunt-owned files.

How to fix it

Let remote_state own the backend

Remove the hand-written backend block from the module and let remote_state generate it with overwrite_terragrunt.

remote_state {
  backend = "s3"
  generate = { path = "backend.tf", if_exists = "overwrite_terragrunt" }
  config = {
    bucket = "acme-tfstate"
    key    = "${path_relative_to_include()}/terraform.tfstate"
    region = "us-east-1"
  }
}

Remove the committed backend block

1. Delete any backend "..." {} block inside the module source.
2. Keep the single generated backend from remote_state.
3. Re-run init so only one backend exists.

How to prevent it

• Keep backend configuration exclusively in remote_state.
• Do not commit a backend block in modules Terragrunt drives.
• Use if_exists = "overwrite_terragrunt" for the generated file.

Related guides