Ansible Loops

Overview

Loops in Ansible allow you to perform tasks repeatedly with different values. They're essential for efficient automation and reducing playbook complexity.

Basic Loops

Standard Loop

# Simple list loop
- name: Create multiple users
  ansible.builtin.user:
    name: "{{ item }}"
    state: present
  loop:
    - john
    - jane
    - bob

# Dictionary loop
- name: Configure user details
  ansible.builtin.user:
    name: "{{ item.name }}"
    groups: "{{ item.groups }}"
    shell: "{{ item.shell }}"
  loop:
    - { name: 'john', groups: 'admin', shell: '/bin/bash' }
    - { name: 'jane', groups: 'dev', shell: '/bin/zsh' }

Loop with Index

# Using loop_control
- name: Create numbered files
  ansible.builtin.copy:
    content: "File content"
    dest: "/tmp/file{{ ansible_loop.index }}.txt"
  loop:
    - alpha
    - beta
    - gamma
  loop_control:
    index_var: ansible_loop.index

Advanced Loop Techniques

Nested Loops

# Using nested items
- name: Configure virtual hosts
  ansible.builtin.template:
    src: vhost.conf.j2
    dest: "/etc/nginx/sites-available/{{ item.0.domain }}_{{ item.1 }}.conf"
  loop: "{{ domains | product(environments) | list }}"
  vars:
    domains:
      - { domain: 'example.com', root: '/var/www/example' }
      - { domain: 'test.com', root: '/var/www/test' }
    environments:
      - dev
      - staging
      - prod

Loop Controls

# Loop with label
- name: Install packages with status
  ansible.builtin.apt:
    name: "{{ item }}"
    state: present
  loop:
    - nginx
    - postgresql
    - redis-server
  loop_control:
    label: "Installing {{ item }}"
    pause: 2  # 2 second pause between iterations

# Loop with index
- name: Create sequential files
  ansible.builtin.copy:
    content: "Content for file {{ ansible_loop.index }}"
    dest: "/tmp/file{{ ansible_loop.index }}.txt"
  loop:
    - first
    - second
    - third
  loop_control:
    index_var: ansible_loop.index

Conditional Loops

# Loop with conditionals
- name: Start services if enabled
  ansible.builtin.service:
    name: "{{ item.name }}"
    state: started
  loop: "{{ services }}"
  when: item.enabled | bool
  vars:
    services:
      - { name: 'nginx', enabled: true }
      - { name: 'mysql', enabled: false }
      - { name: 'redis', enabled: true }

Loop with Filters

Filtering Lists

# Select specific items
- name: Process active users
  debug:
    msg: "Processing user {{ item }}"
  loop: "{{ users | selectattr('active', 'eq', true) | list }}"
  vars:
    users:
      - { name: 'john', active: true }
      - { name: 'jane', active: false }
      - { name: 'bob', active: true }

Transform and Loop

# Map and loop
- name: Display uppercase names
  debug:
    msg: "Name: {{ item }}"
  loop: "{{ users | map(attribute='name') | map('upper') | list }}"

Error Handling in Loops

Continue on Error

# Ignore failures
- name: Install packages with failure handling
  ansible.builtin.apt:
    name: "{{ item }}"
    state: present
  loop:
    - package1
    - package2
  ignore_errors: yes

Retry Logic

# Retry failed operations
- name: Attempt operations with retry
  ansible.builtin.command: "{{ item }}"
  loop:
    - "service1 start"
    - "service2 start"
  register: result
  until: result.rc == 0
  retries: 3
  delay: 5

Best Practices

Performance Optimization

# Use with_items for large lists
- name: Process large lists efficiently
  debug:
    msg: "Processing {{ item }}"
  with_items: "{{ large_list }}"

# Parallel execution
- name: Run tasks in parallel
  command: "long_running_task.sh"
  async: 3600
  poll: 0
  loop: "{{ tasks }}"
  register: async_results

- name: Wait for completion
  async_status:
    jid: "{{ async_result_item.ansible_job_id }}"
  loop: "{{ async_results.results }}"
  loop_control:
    loop_var: "async_result_item"
  register: async_poll_results
  until: async_poll_results.finished
  retries: 30

Loop Documentation

# Document complex loops
- name: Complex loop operation
  vars:
    loop_description: |
      This loop:
      1. Filters active items
      2. Transforms data
      3. Processes results
  debug:
    msg: "{{ loop_description }}"
  loop: "{{ complex_data | selectattr('active', 'eq', true) | map(attribute='name') | list }}"