Interview › Infrastructure as Code (Terraform, Ansible)

What is delegate_to, and when would you use it?

Infrastructure as Code (Terraform, Ansible) · Advanced level

Answer

delegate_to runs a task on a different host than the current inventory host. I use it for load balancer registration, API calls from localhost, database migration coordination, bastion-side checks, or centralized monitoring updates during a rollout.

Technical explanation

delegate_to: localhost is common for API calls from the control node.

delegate_facts controls whether gathered facts attach to the delegated host or original host.

Delegation is a clean way to coordinate external systems during per-host operations.

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. Orchestrate a rolling update for: What is delegate_to, and when would you use it?

2. Playbook skeleton:

- name: Rolling app upgrade

hosts: app

serial: 2

max_fail_percentage: 20

tasks:

- name: Drain host from load balancer

ansible.builtin.command: /usr/local/bin/lbctl drain {{ inventory_hostname }}

delegate_to: localhost

- name: Upgrade app package

ansible.builtin.package:

name: myapp

state: present

notify: Restart app

- meta: flush_handlers

- name: Wait for health

ansible.builtin.uri:

url: http://{{ inventory_hostname }}:8080/health

status_code: 200

retries: 12

delay: 5

register: health

until: health.status == 200

- name: Add host back to load balancer

ansible.builtin.command: /usr/local/bin/lbctl enable {{ inventory_hostname }}

delegate_to: localhost

3. Test against a staging group with serial: 1, then increase batch size after measuring recovery time.

4. Confirm a failed health check stops the rollout before most hosts are touched.

More Infrastructure as Code (Terraform, Ansible) interview questions

• What is Infrastructure as Code, and what problems does it solve over click-ops?
• What is the difference between declarative and imperative IaC, and where do Terraform and Ansible fall?
• What is the difference between configuration management and provisioning?
• What is Terraform, and what is the core plan/apply workflow?
• What does terraform init do?
• What is the Terraform state file, and why is it critical?
• Why should state be stored remotely, and what backend would you use on AWS?
• What is state locking, and why does it matter for teams?

← All Infrastructure as Code (Terraform, Ansible) questions