Terraform fails early when for_each cannot determine resource identity at plan time.
This failure is not about syntax. It is about identity.
for_each does not loop.
It assigns addresses in state.
If the keys are unknown, Terraform cannot assign those addresses.
If the keys change, Terraform treats them as different resources.
This leads to two common outcomes:
- plan fails before apply
- resources are destroyed and recreated instead of updated
The fix is not adding conditionals.
The fix is shaping your data so identity is stable and known before execution.
This lesson breaks down how Terraform evaluates for_each, how keys become state addresses, and why expression design directly controls lifecycle behavior.
Watch the full lesson here: