Terraform "Reference to undeclared resource" in CI

By Daniel Zoghalchali·Latchkey

An expression references a resource or data source address that does not exist in the configuration. The resource was never declared, was renamed/removed, or the type prefix is wrong.

What this error means

validate/plan fails with "Reference to undeclared resource", naming the address it could not resolve. It surfaces after renaming or deleting a resource, or from a typo in the resource type or name.

terraform output

Error: Reference to undeclared resource

  on outputs.tf line 2, in output "bucket_arn":
   2:   value = aws_s3_bucket.logs.arn

A managed resource "aws_s3_bucket" "logs" has not been declared in the root module.

Common causes

Resource renamed or removed

A reference still points at the old address after a resource was renamed or deleted, so Terraform cannot resolve it.

Typo or wrong type/data prefix

A misspelled name, a wrong resource type, or referencing a data source without the data. prefix produces an undeclared-resource error.

How to fix it

Fix the reference to a declared address

Point the reference at the resource’s real address; for data sources include the data. prefix.

outputs.tf

# resource reference
value = aws_s3_bucket.audit_logs.arn
# data source reference
value = data.aws_caller_identity.current.account_id

Reconcile after renames

Search the config for the old address and update every reference.
If the resource was renamed, add a moved block so state follows the rename.
Run terraform validate to catch any remaining undeclared references.

How to prevent it

Run terraform validate in CI to catch undeclared references early.
Update all references (and add moved blocks) when renaming resources.
Use editor/IDE Terraform tooling to flag unresolved addresses.

Frequently asked questions

What causes ""Reference to undeclared resource""?