i dont think theyre equivalent tools since Terraform is used for things like creating cloud VMs with the selected OS image, configuring subnets and route tables among other things which i dont believe NixOS is meant for

ive not done secrets management before but i came across this list on hackernews, a few non-cloud ones use open source license https://news.ycombinator.com/item?id=37133054#37151218

but another user there have mentioned that while most of them integrate with Kubernetes and AWS, short lived DB credentials are not in any of those listed