YAML | Notion

YAML is a serialization language used for configuration files, widely used format on multiple applications (docker, k8s, ansible, in devops etc)
YAML is a serialization language just like XML and JSON
- Standard format to transfer data
File extension: .yml or .yaml
It’s human readible and intuitive
Example of data in different formats:
Line separation and spaces matter in yaml
You can check the validity of the your yaml file (syntax wise) here: https://onlineyamltools.com/validate-yaml

YAML Syntax

# This is a comment 
# Everything is a key-value pair 

# string - You don't have to close it with quotes! 
# Unless you want to use special string characters 
# integers can be written like normal
app: user-authentication
port: 9000
version: 1.7 

#Objects - You can group k-v pairs by indenting them and enclosing it
microservice:
	app: user-authentication
	port: 9000
	version: 1.7

#Lists in YAML, by using the hypen '-'
# This will allow us to create mulitple objects, by just adding a hypen
microservice:
	- app: user-authentication
		port: 9000
		version: 1.7
	- app: shopping-cart
		port: 9001
		versions: 
		- 1.8
		- 1.9
		- 1.2

# Multiline string - using the pipe operator 
multilineString: |
	this is a multiline string
	hello my name is tahir 
	next line

# You can configure shell commands to run within the file! 
# Example:
command: 
	- sh
	- -c
	- |
		#!/user/bin/env bash -e
		http() {
			local path="${1}"
			set -- -XGET -s --fail
			#some more stuff here
			curl -k "$@" "http://localhost:5601${path}"
		}
		http: '/app/kibana'

# Can use environmental variables by using the dollar sign
command:
	- /bin/sh
	- ec
	- >-
		mysql -h 127.0.0.1 -u root -p$MYSQL_ROOT_PASSWORD -e 'SELECT 1' 

# Place holders can be used by using double squigly brackets
# Multiple components can be seperated by 3 dashes ---

Real life example of YAML pod configuration:

YAML Key Syntax
1. What is YAML?
  - YAML stands for "YAML Ain't Markup Language."
  - It is a human-readable data serialization format.
  - YAML files use indentation and simple syntax to represent data structures.
2. Basic Syntax:
  - YAML files use a combination of indentation and colons to represent data.
  - YAML supports lists, dictionaries, and scalar values.
  Example:
```
# YAML example
fruits:
  - apple
  - orange
  - banana
person:
  name: John Doe
  age: 30
  city: New York
```
- Scalars:
  - Scalars represent single values such as strings, numbers, booleans, and null.
  Example:
```
# YAML example
name: John Doe
age: 30
isStudent: true
favoriteFruit: null
```
- Lists:
  - Lists represent an ordered collection of values.
  Example:
```
# YAML example
fruits:
  - apple
  - orange
  - banana
```
- Dictionaries (Mappings):
  - Dictionaries represent key-value pairs.
  Example:
```
# YAML example
person:
  name: John Doe
  age: 30
  city: New York
```
- Nested Structures:
  - YAML allows nesting data structures within each other.
  Example:
```
# YAML example
person:
  name: John Doe
  age: 30
  address:
    street: 123 Main St
    city: New York
    country: USA
```
- Comments:
  - YAML supports comments for adding notes or explanations to the file.
  Example:
```
# YAML example
# This is a comment
fruits:
  - apple # Comment after a value
  - orange
  - banana
```
- YAML Anchors and Aliases:
  - YAML supports anchors and aliases to reuse and reference data.
  Example:
```
# YAML example
person: &PERSON
  name: John Doe
  age: 30
employee1:
  <<: *PERSON
  position: Developer
employee2:
  <<: *PERSON
  position: Designer
```
- Multiple Documents:
  - YAML allows multiple documents within a single file, separated by --.
  Example:
```
# YAML example
---
fruits:
  - apple
  - orange
  - banana
---
person:
  name: John Doe
  age: 30
  city: New York
```
1. Advanced Features:
  - YAML supports more advanced features like tags, references, and custom data types.
  - These features provide additional flexibility and extensibility.
  Example:
```
# YAML example
%YAML 1.2
---
!!python/object:__main__.Person
  name: John Doe
  age: 30
  city: New York
```
This crash course provides a brief overview of YAML and its basic syntax. YAML is commonly used for configuration files, data serialization, and interchanging data between programming languages. By understanding the concepts covered in this crash course, you can effectively work with YAML files and leverage its simplicity and readability for various purposes.

YAML Key Syntax