YAML extensive cheatsheet

Here’s an extensive YAML (YAML Ain’t Markup Language) cheatsheet, covering basic syntax, advanced concepts, and usage tips:

Basic YAML Syntax

1. Key-Value Pair

    key: value
   

2. Nested Objects

    parent:
      child: value
   

3. Lists (Arrays)

    items:
      - item1
      - item2
      - item3
   

4. Inline Lists

    items: [item1, item2, item3]
   

5. Inline Dictionaries

    person: {name: John, age: 30}
   

6. Comments

    # This is a comment
   

Data Types

1. String

    name: "John"
   

2. Multiline String

    description: |
      This is a long
      multiline string.
   

   or folded style:

    description: >
      This is a long
      folded string.
   

3. Integer

    age: 30
   

4. Float

    price: 99.99
   

5. Boolean

    active: true
   

6. Null

    key: null
   

Advanced Syntax

1. Anchors and Aliases
   • Anchor: &anchor_name
   • Alias: *anchor_name

    default_settings: &defaults
      retries: 3
      timeout: 60
   
    user_settings:
      <<: *defaults
      timeout: 30  # Override the default timeout
   

2. Merging Keys

    defaults: &defaults
      setting1: default1
      setting2: default2
   
    custom:
      <<: *defaults
      setting2: custom2  # Overridden
      setting3: custom3
   

3. Multiple Documents in One File

    ---
    document1:
      key1: value1
    ---
    document2:
      key2: value2
   

4. Reference Reuse

    values:
      - &id001 42
      - *id001
   

5. Multiline Folded Block

    description: >
      This is a multiline string
      with a folded style that will
      be rendered as a single line.
   

6. Multiline Literal Block

    description: |
      This is a multiline string
      with literal style that will
      retain the newline characters.
   

Common YAML Patterns

1. Config Files

    version: 1.0
    environment: production
    server:
      port: 8080
      host: localhost
   

2. Docker Compose Example

    version: "3.8"
    services:
      web:
        image: nginx
        ports:
          - "8080:80"
      db:
        image: postgres
        environment:
          POSTGRES_USER: user
          POSTGRES_PASSWORD: password
   

3. Kubernetes Pod Configuration

    apiVersion: v1
    kind: Pod
    metadata:
      name: mypod
    spec:
      containers:
        - name: mycontainer
          image: nginx
          ports:
            - containerPort: 80
   

4. CI/CD Pipeline Example

    stages:
      - build
      - test
      - deploy
   
    build_job:
      stage: build
      script:
        - make build
   
    test_job:
      stage: test
      script:
        - make test
   
    deploy_job:
      stage: deploy
      script:
        - make deploy
   

Special Characters

1. Reserved Characters
   • : - Indicates a key-value separator.
   • - - Indicates an item in a list.
   • # - Used for comments.
   • & - Used for anchors.
   • * - Used for aliases.
   • | - Indicates a literal block scalar (preserves newlines).
   • > - Indicates a folded block scalar (folds newlines).

2. Escaping Characters

    text: "This is a string with a special character: \t (tab)"
   

YAML Best Practices

1. Consistent Indentation
   • Always use spaces for indentation, never tabs.
   • YAML does not allow mixed spaces and tabs.
2. Avoid Trailing Whitespace
   • YAML is sensitive to trailing spaces, which may cause parsing errors.
3. Keep It Simple
   • Avoid overcomplicating YAML with deeply nested structures. Aim for readability.
4. Use Anchors and Aliases to DRY (Don’t Repeat Yourself)
   • Use anchors and aliases to reduce repetition.
5. Avoid Boolean Strings

   • Words like yes, no, on, off, true, false can be misinterpreted as booleans. It’s best to wrap them in quotes:

     setting: "yes"
     

Error Handling and Debugging

1. Indentation Errors
   • YAML is strict about indentation levels. Always use consistent indentation (usually 2 or 4 spaces).
2. Invalid Characters
   • Avoid using special characters in keys unless quoted:

    "key-with-special:characters": value
   

3. Common Parsing Errors
   • Ensure no tabs are used for indentation; YAML only supports spaces.
   • Check for colons : outside of keys.