Terraform Destroy 🗑️, 409 Conflict Error when deleting an OCI Subnet 🛜

I was playing around with Terraform in my lab the other day and attempted to run a destroy operation to tear down everything I’d built – this was to avoid any unnecessary charges for resources that I’m not actively using in my test tenancy 💷.

The destroy operation kept failing with a 409-Conflict error which stated that the subnet it was trying to delete had references to a VNIC, this made no sense at all as everything had been provisioned with Terraform…..and the VM instances attached to the subnet had been deleted earlier in the destroy operation 😤.

I figured out what was actualluy blocking the deletion…..it was a VNIC attached to the subnet, however it wasn’t a VNIC that I (or Terraform!) had created.

As part of the testing I’d done post-build, I had attached the Cloud Shell to a Virtual Cloud Network & Subnet – this enabled me to SSH into a VM instance that didn’t have a public IP address assigned (as I’ve previously wrote about here).

The fix for this was simple, I just needed to close the Cloud Shell session (which detaches the VNIC from the subnet) and retry the destroy operation – which worked this time ✅.