Core workflow

Play it

Drift Detective: Keep config, state and reality in agreement through drift, imports and locks.

The game links back to this page from: Try it: examples/local-file, State.

Terraform describes infrastructure declaratively in .tf files and reconciles real resources to match. The core loop:

terraform init                 # download providers, set up the backend
terraform fmt                  # canonical formatting
terraform validate             # syntax + internal consistency, no provider calls
terraform plan -out tfplan     # compute the diff between config and real state
terraform apply tfplan         # apply exactly that plan
terraform destroy               # tear everything down

Always plan before apply and read the diff — + create, - destroy, ~ update in place, -/+ destroy-and-recreate (the latter matters: some attribute changes force replacement, e.g. renaming an AWS S3 bucket).

Try it: examples/local-file

Uses hashicorp/local so it runs with no cloud credentials:

cd topics/terraform/examples/local-file
terraform init
terraform plan
terraform apply -auto-approve
cat greeting.txt
terraform destroy -auto-approve

Change var.greeting (-var 'greeting=hi' or edit the default) and re-run plan to see a ~ update-in-place instead of a fresh create.

State

Terraform tracks what it created in a state file (terraform.tfstate — never commit it; see .gitignore). State maps each resource block to a real-world ID; plan diffs config vs. state, then separately checks state against real infrastructure (a refresh, done automatically as part of plan/apply).

terraform state list                    # resources currently tracked
terraform state show local_file.greeting  # one resource's tracked attributes
terraform import <addr> <id>             # bring an existing resource under management

If state and reality disagree (someone changed a resource outside Terraform), the next plan shows Terraform's proposal to reconcile them — read it before applying, it may mean "revert the manual change" rather than what you expected.