Ansible Debugging

Overview

Ansible errors fall into four categories: connection, authentication, module, and syntax. Systematic diagnosis starts with identifying the category, then isolating the specific cause.

When to Use

• UNREACHABLE errors (SSH/network issues)
• Permission denied or sudo password errors
• MODULE FAILURE messages
• Undefined variable errors
• Template rendering failures
• Slow playbook execution

Error Categories

Quick Diagnosis

Connection Errors

# Test SSH directly
ssh -v -i /path/to/key user@hostname

# Test port connectivity
nc -zv hostname 22

# Verify inventory parsing
ansible-inventory --host hostname

Common causes:

• Wrong IP/hostname in inventory
• Firewall blocking port 22
• SSH key permissions (must be 600)

Authentication Errors

# Test with explicit options
ansible hostname -m ping -u user --private-key /path/to/key

# For sudo password issues, either:
ansible-playbook playbook.yml --ask-become-pass
# Or configure NOPASSWD in /etc/sudoers

Module Errors

# Check module documentation
ansible-doc ansible.builtin.copy

# Verify module parameters match your Ansible version
ansible --version

Variable Errors

# Use default filter for optional variables
{{ my_var | default('fallback') }}

# Debug variable values
- ansible.builtin.debug:
    var: problematic_variable

Verbosity Levels

Start with -v, increase only if needed.

Debugging Commands

# Syntax check only
ansible-playbook --syntax-check playbook.yml

# Dry run
ansible-playbook --check playbook.yml

# Step through tasks
ansible-playbook --step playbook.yml

# Start at specific task
ansible-playbook --start-at-task "Task Name" playbook.yml

# Limit to specific host
ansible-playbook --limit hostname playbook.yml

Common Error Patterns

Performance Debugging

# ansible.cfg
[defaults]
callback_whitelist = profile_tasks  # Show task timing

[ssh_connection]
pipelining = True                   # Faster SSH

# Skip fact gathering if not needed
- hosts: all
  gather_facts: no