Yaml file Basics for Devops and Kubernetes

Basics

YAML file is a text-based file used for configuration files, data serialization, and exchange between different as a format for storing structured data.

Example

---
name: John Doe
age: 30
email: john@example.com
Sample_names:
- John
- Sam
- Dwayne

Lists in YAML

• Lists begin with a hyphen
• Dependent on whitespace/indentation

Json Example

{
"Sample_names" : [
    "John",
    "Sam",
    "Dwayne"
  ]
}

YAML Example

---
Sample_names:
- John
- Sam
- Dwayne

Dictonary in YAML

example of a simple dictonary

JSON

{
  "name": "John Doe",
  "age": 30,
  "email": "john@example.com"
}

YAML

---
name: John Doe
age: 30
email: john@example.com

With nested Dictonary

JSON

{
  "name": "John Doe",
  "age": 30,
  "contact": {
    "email": "john@example.com",
    "phone": "0987654321",
    "address": "milkey way, far behind the son"
  }
}

YML

---
name: John Doe
age: 30
contact:
  email: john@example.com
  phone: '0987654321'
  address: milkey way, far behind the son

In the second dictonary there is a space/indentation in dictonary items.

Nested yaml

JSON

{
  "name": "John Doe",
  "age": 30,
  "email": "john@example.com",
  "Sample_names" : [
    "John",
    "Sam",
    "Dwayne"
  ],
  "Dataset" : {
    "data1": 12,
    "data2": 13,
    "LoopDataset" : {
      "DS01" : 200,
      "DS02" : 300,
      "DS03" : [
          "Hew01",
        "Hew02",
        "Hew03"
      ]
    }
    }
}

YAML

---
name: John Doe
age: 30
email: john@example.com
Sample_names:
- John
- Sam
- Dwayne
Dataset:
  data1: 12
  data2: 13
  LoopDataset:
    DS01: 200
    DS02: 300
    DS03:
    - Hew01
    - Hew02
    - Hew03

Comments on YML

The # character is used to comment on yml document

---
# user details
name: John Doe
age: 30
# contact data
contact:
  email: john@example.com   # some comments for email
  phone: "0987654321"
  address: milkey way, far behind the son

Tripple hyphens in YML file

• The three hyphens --- is a document separator.
• It is used to separate multiple YAML documents within a single file.
• Each document represents a separate YAML data structure, such as an object, a list, or a configuration.
• It is commonly used when you want to group related data or configurations together, making it easier to manage and organize your YAML files.
• When parsing YAML files, libraries and tools can process each document individually by recognizing the --- separator. This allows you to extract or manipulate specific documents within the file as separate entities.

---
# Document 1
person:
  name: John Doe
  age: 30

---
# Document 2
animal:
  species: dog
  breed: Labrador Retriever

A List of Dictonaries

• A list with key-value pairs is often referred to as a list of dictionaries or a list of maps.
• It represents a sequence of dictionaries, where each dictionary contains key-value pairs.
• This structure allows you to have multiple dictionaries within a list, with each dictionary having its own set of keys and corresponding values.

- name: John Doe 
  age: 30  
  city: New York 
- name: Jane Smith  
  age: 25  
  city: London  
- name: Alex Johnson  
  age: 35   
  city: Paris

• At the above example we have a list of three dictionaries.
• Each dictionary represents a person with keys (name, age, city) and their respective values.
• The dash (-) is used to indicate the start of each dictionary within the list.
• When parsing or interpreting this YAML structure, it would result in a list of dictionaries, allowing you to access the data by iterating over the list and accessing the key-value pairs within each dictionary.

Some useful utilities

yq command-line tool

A lightweight and portable command-line YAML processor.

Link : https://github.com/mikefarah/yq

useful website

• www.yamllint.com : Check yml file for errors.
• www.json2yaml.com : Convert json to yml.