Interview › Infrastructure as Code (Terraform, Ansible)
When would you use ignore_changes, and what is the risk?
Infrastructure as Code (Terraform, Ansible) · Basic level
Answer
ignore_changes is useful when an external controller manages an attribute, such as an autoscaler changing desired capacity or Kubernetes adding annotations. The risk is that Terraform will intentionally stop detecting meaningful drift for that field, so it can hide misconfiguration or security changes if used too broadly.
Technical explanation
Use it for fields owned by controllers, not for fields that encode compliance or security posture.
Review ignored attributes periodically because they become blind spots.
Prefer module design that separates ownership before reaching for ignore_changes.
Keep Terraform's ownership boundary clear: one state should own a resource or field, and other tools should consume published outputs instead of modifying it.
Use fmt, validate, linting, policy checks, plan review, and state locking before production applies.
Design for small blast radius by splitting state around lifecycle, permissions, and recovery boundaries.
Hands-on example
1. Practice lifecycle and dependency controls for: When would you use ignore_changes, and what is the risk?
2. Add lifecycle rules deliberately:
resource "aws_db_instance" "prod" {
identifier = "prod-db"
lifecycle {
prevent_destroy = true
ignore_changes = [allocated_storage]
}
}
3. Force a reviewed replacement with:
terraform plan -replace='aws_instance.web["blue"]' -out=replace.tfplan
terraform apply replace.tfplan
4. Use depends_on only when references do not express the ordering. Then run terraform graph or inspect the plan to explain the dependency path.
5. If you use -target for recovery, immediately follow with a full terraform plan.
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