Working with Stacked Loops in Ansible

In my homelab environment, I recently encountered an interesting challenge: I needed to execute multiple Hugo commands across multiple website directories. This led me to explore one of Ansible’s powerful features - stacked loops. In this post, I’ll share my experience and show you how to effectively use stacked loops in Ansible.

The Challenge

I maintain several Hugo-based websites in my homelab, each requiring the same set of commands for updates and maintenance. Manually running these commands for each site was becoming tedious and error-prone. I needed a way to automate:

Running multiple Hugo commands (mod get, tidy, npm pack, etc.)
Executing these commands across multiple site directories
Maintaining flexibility to add more sites or commands in the future

Understanding Stacked Loops

Stacked loops in Ansible allow you to iterate over multiple lists simultaneously. Think of it as nested loops where you can:

Loop over a list of directories (outer loop)
For each directory, loop over a list of commands (inner loop)

Implementation

The complete code for this implementation is available in my github repository ansible.hugo_webhosts role.

1. Variable Structure

First, I defined my variables to maintain a clean separation of data:

# defaults/main.yml
hugo:
  commands:
    - hugo mod get -u 
    - hugo mod tidy
    - hugo mod npm pack
    - npm install
    - hugo

sites:
  - name: alain.apigban.com
    local_path: /var/www/html
    repo_url: https://github.com/apigban/alain.apigban.com.git
    port: 10000
  - name: example.apigban.com
    local_path: /var/www/html
    repo_url: https://github.com/apigban/example.git
    port: 20000

2. Main Playbook

The main playbook structure is straightforward:

# main.yml
- name: Update Hugo Sites
  hosts: web01
  gather_facts: true

  tasks:
  - name: Execute Hugo Commands
    ansible.builtin.include_tasks: hugo-commands.yml
    loop: "{{ sites }}"
    loop_control:
      loop_var: outer_item

3. Task Implementation

The included task file handles the nested loop:

# hugo-commands.yml
- name: Execute commands for each site
  ansible.builtin.command: "{{ item }}"
  args:
    chdir: "{{ outer_item.local_path }}/{{ outer_item.name }}"
  loop: "{{ hugo.commands }}"
  register: command_output

Understanding the Output

When you run this playbook, Ansible executes each command for each site. The output looks like this:

TASK [Execute commands] ******************
ok: [web01] => (item=hugo mod get -u) => {
    "msg": "PATH: /var/www/html/alain.apigban.com COMMAND: hugo mod get -u"
}
ok: [web01] => (item=hugo mod tidy) => {
    "msg": "PATH: /var/www/html/alain.apigban.com COMMAND: hugo mod tidy"
}
[... additional output ...]

Alain Igban