Terraform "Unsupported attribute" module output not declared in CI

By Daniel Zoghalchali·Latchkey

An expression reads module.network.subnet_ids, but the network module declares no output "subnet_ids". Terraform reports an unsupported attribute because a module exposes only the outputs it explicitly declares.

What this error means

plan or validate stops with "Error: Unsupported attribute" and "This object does not have an attribute named \"X\"." on a module.<name>.<output> reference.

Error: Unsupported attribute

  on main.tf line 20, in resource "aws_route_table_association" "a":
  20:   subnet_id = module.network.subnet_ids[0]

This object does not have an attribute named "subnet_ids".

Common causes

The module does not declare that output

You read module.network.subnet_ids but the module has no matching output block, or the output was renamed.

A module version dropped or renamed an output

A module upgrade removed or renamed the output your code still references.

How to fix it

Declare the output in the module

1. Open the module and check its output blocks.
2. Add an output for the value you need, or fix the name you reference.
3. Re-run validate to confirm the attribute resolves.

output "subnet_ids" {
  value = aws_subnet.this[*].id
}

Match the reference to an existing output

Correct the caller to use an output name the module actually exposes after an upgrade.

How to prevent it

• Declare an output for every module value callers consume.
• Review module changelogs for renamed or removed outputs.
• Run terraform validate after module upgrades.

Frequently asked questions

Related guides

References

• Terraform documentation
• GitHub Actions documentation