Part 07: Ansible and YAML

YAML Introduction

YAML is the abbreviated form of “YAML Ain’t markup language” is a data serialization language which is designed to be human-friendly and works well with other programming languages for everyday tasks. YAML is a less complex than XML or JSON and it allows you to provide configuration settings.

YAML Basic Rules

• YAML files should end in .yaml or .yml.
• YAML is case sensitive.
• YAML does not allow the use of tabs, 2 spaces are used instead of tabs.
• Hash # is used as comments.
• YAML files are supposed to start with three dashes ---.
• In general, YAML strings don’t have to be quoted, although you can quote them if you prefer.
• In some scenarios in Ansible, you will need to quote strings. These typically involve the use of double curly braces for variable substitution.
• YAML has a native Boolean type and provides you with a wide variety of strings that can be interpreted as true or false, and not case sensitive, true or True and false or False.

YAML Basic Data Types

key-value Pair

A single value and a variable, it can be string, integer, float or bool.

max_retry: 100            # integer
database: user            #string
pass: true                # bool
date: 1990-02-06 14:33:22 # ISO 8601 standard for time and date

Mapping

YAML dictionaries are like objects in JSON, dictionaries in Python, or hashes in Ruby. Technically, these are called mappings in YAML, but I call them dictionaries here to be consistent with the official Ansible documentation. They look like this:

animals:
  name: cat
    color: white
  name: dog
    color: black

Sequence

YAML lists are like arrays in JSON and Ruby or lists in Python. Technically, these are called sequences in YAML, but I call them lists here to be consistent with the official Ansible documentation. They are delimited with hyphens, like this

# list
employee:
  - name: Jack
  - name: Syd

employee: ["Jack", "Syd"]    # list  

# complex list (mapping and sequence)
employee:
  - name: Jack
    age: 28
  - name: Syd
    age: 34

# complex list (mapping and sequence)    
employee:
  - {name: "Jack", age: "22"}
  - {name: "Syd", age: "42"}

Line Folding and Break

When writing playbooks, you’ll often encounter situations where you’re passing many arguments to a module. You might want to break this up across multiple lines in your file, but you want Ansible to treat the string as if it were a single line, For example:

employee:
  - name: Jack
    age: 28 
description: >      # This is a single line 
  This is a 1st line
  this is a not 2nd line and part of 1st line
  this is a also part of 1st line.

You can also do line breaks with YAML by using the ( | ) character. The YAML parser will place line breaks.

employee:
  - name: Syd
    age: 42 
signature: | # line breaks
  Mike
  Academy
  E-mail - abc@abc  

See more on YAML