Ansible

YAML Syntax Traps

• Jinja2 in value needs quotes — "{{ variable }}" not {{ variable }}
• : in string needs quotes — msg: "Note: this works" not msg: Note: this
• Boolean strings: yes, no, true, false parsed as bool — quote if literal string
• Indentation must be consistent — 2 spaces standard, tabs forbidden

Variable Precedence

• Extra vars (-e) override everything — highest precedence
• Host vars beat group vars — more specific wins
• vars: in playbook beats inventory vars — order: inventory < playbook < extra vars
• Undefined variable fails — use {{ var | default('fallback') }}

Idempotence

• command/shell modules aren't idempotent — always "changed", use creates: or specific module
• Use apt, yum, copy etc. — designed for idempotence
• changed_when: false for commands that don't change state — like queries
• creates:/removes: for command idempotence — skips if file exists/doesn't