Terraform (OpenTofu)

Infrastructure as Code via Terraform (or its open-source fork OpenTofu, since HashiCorp's BSL license change in 2023) is the standard for declarative cloud resource management. The key mental model: describe the desired state of your infrastructure, and Terraform figures out what to create, modify, or destroy. The 2023 HashiCorp license change prompted the Linux Foundation to fork Terraform as OpenTofu — for most teams, the practical difference is minimal, but open-source-first teams have migrated to OpenTofu. The critical Terraform skill most engineers skip: remote state management with locking (S3 + DynamoDB or Terraform Cloud) to prevent concurrent apply conflicts. State corruption is the most common Terraform production incident.