YAML 101

Key/value pairs

• YAML document consists of key/value pairs

• Key/value pairs are separated by colon followed by space

• Supports different data types

  • Integers

  • Floating-point numbers

  • Strings, enclosed with quotes if they have special symbols

  • Boolean

  • Binary

  • Dates, in ISO:8601 format

  • Null value

Name: Dave
Age: 25
GPA: 4.2
Occupation: Engineer
State: 'New Jersey'
About: "I'm a software engineer"
Score: null
Male: true
DateOfBirth: 1990-09-15T19:07:00

Lists

• YAML lists are indented with a dash

• All items are on the same level

• There are 2 types of writing arrays:

  • Block sequence - each entry indicated with a dash followed by a space

  • Flow sequence - all elements are on the same line, separated with commas and enclosed by [].

PeopleBlock:
  - John
  - Mike
  - Tom
  - Jake

PeopleFlow: [John, Mike, Tom, Jake]

Dictionaries

• A set of properties grouped under an item

• Dictionaries contain key/value pairs

Dave:
  Age: 25
  GPA: 4.2
  Occupation: Engineer
  State: 'New Jersey'
  About: "I'm a software engineer"
  Score: null
  Male: true
  DateOfBirth: 1990-09-15T19:07:00

Lists with Dictionaries

Personnel:
  - Dave:
      Age: 24
      Occupation: Engineer
      State: CA
  - Mike:
      Age: 30
      Occupation: Manager
      State: TX
  - John:
      Age: 40
      Occupation: Designer
      State: WA

Lists with Dictionaries containing Lists

Personnel:
  - Dave:
      Age: 24
      Occupation: Engineer
      State: CA
      Degrees:
      	- Bachelor
      	- Masters
      	- PHD
  - Mike:
      Age: 30
      Occupation: Manager
      State: TX
      Degrees: [Bachelor, Masters]
  - John:
      Age: 40
      Occupation: Designer
      State: WA
      Degrees:
      	- Masters

Pipes

• Pipe notation is also referred as literal block

• All new lines, indentation, extra spaces are preserved

Resource:
  Name: My resource
  Description: |
    This is a description,
    with new lines and | special symbols
  Prop: value

Greater than

• Also referred as folded block

• Renders the text as a single line

• All new lines will be replaced with a single space

• Blank lines are converted to a new line character

Resource:
  Name: My resource
  Description: >
    This is a description,
    with new lines and | special symbols

    Will render everything as a single line
  Prop: value

Comments

• Comments are defined with '#' symbol

# resource definition
Resource:
  Name: My resource

Anchor / merge

• Allows to define and reference blocks

• CloudFormation has very limited support for anchors

MyAnchor: &a
  Prop1: value1
  Prop2: value2

AnotherPlace:
  <<: *a
  Prop3: value3