Interview › Infrastructure as Code (Terraform, Ansible)
What is a register, and how do you use the result of one task in another?
Infrastructure as Code (Terraform, Ansible) · Advanced level
Answer
register stores the result of a task in a variable. The result can include stdout, stderr, return code, changed status, skipped status, and module-specific fields. I use it to make later tasks conditional on real command or module output.
Technical explanation
Registered variables are scoped to the host executing the task.
Check stdout_lines for line-oriented output and rc for command status.
Registered results are commonly combined with when, changed_when, and failed_when.
Prefer idempotent modules over shell so repeated runs are safe and change reporting is meaningful.
Separate reusable role logic from inventory-specific variables so the same automation works across environments.
Run lint, syntax checks, check mode where useful, and staged rollouts before production-wide changes.
Hands-on example
1. Use register, when, and loop for: What is a register, and how do you use the result of one task in another?
2. Example:
- name: Check app health
ansible.builtin.uri:
url: http://localhost:8080/health
status_code: 200
register: health
failed_when: false
- name: Restart app only when health check failed
ansible.builtin.service:
name: app
state: restarted
when: health.status | default(0) != 200
- name: Install required packages
ansible.builtin.package:
name: "{{ item }}"
state: present
loop:
- nginx
- curl
- jq
3. Run once with the service healthy and once after stopping it; confirm the conditional task changes behavior based on the registered result.
4. Use loop_control.label when iterating over dictionaries to keep output readable.
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