How does Terraform integrate into automated CI/CD pipelines?

Integrating Terraform (Infrastructure as Code) into CI/CD enables automated, auditable infrastructure changes. The standard pattern: on a pull request, the pipeline runs terraform plan and posts the plan output as a PR comment — reviewers see exactly what infrastructure changes will be made before approving. On merge to main, the pipeline runs terraform apply -auto-approve to execute the changes. Critical considerations: use a remote state backend (AWS S3 + DynamoDB for locking, Terraform Cloud) so state is shared and concurrent applies are prevented; use OIDC authentication (no long-lived AWS keys in CI secrets); run terraform fmt -check and terraform validate in the pipeline to enforce code quality; and use policy as code (OPA, Sentinel) to prevent non-compliant infrastructure changes from being applied. Tools like Atlantis and Spacelift provide Terraform-specific GitOps workflows with plan/apply automation and audit logging.