Skip to main content

YAML Basics

Document, Mapping, Sequence, and Scalar are the four basic types of YAML documents.

note

This document is not a tutorial on YAML, but rather a brief overview of the YAML terminology in Anemos context. For more information on YAML, please refer to the YAML specification.

Document​

A YAML document in Anemos is a file that contains the representation of a Kubernetes resource such as a Pod, Deployment, or Service.

Technically, a YAML file can contain multiple documents, separated by ---. However, Anemos only supports one document per file. Furthermore, even though a YAML document can have a Mapping, Sequence, or Scalar as its root, in Anemos, a Document can only have a Mapping as its root.

An example of a YAML document:

apiVersion: v1
kind: Pod
metadata:
  name: my-pod
  namespace: default
spec:
  containers:
    - name: my-container
      image: nginx
      ports:
        - containerPort: 80

Mapping​

A mapping is a collection of key-value pairs. Each key is unique within the mapping. Key of a mapping is a Scalar. The value can be a Mapping, Sequence, or Scalar.

# The value of key1 is a scalar.
key1: value1

# The value of key2 is another mapping.
key2:
  subkey1: subvalue1
  subkey2: subvalue2

# The value of key3 is a sequence.
key3:
  - item1
  - item2

Sequence​

A sequence is an ordered collection of items. Each item in a sequence can be a Mapping, Sequence, or Scalar. It is possible to have multiple types of data in a single sequence.

# Scalar item.
- item1

# Mapping item.
- item3:
    subitem1: subvalue1
    subitem2: subvalue2

# Sequence item.
- item4:
    - subitem1
    - subitem2

Scalar​

A scalar is a single value. It can be a string, number, boolean, or null. Scalars have styles that define how they are represented in YAML.

# Plain style
key1: value1

# Double-quoted style
key2: "value2"

# Single-quoted style
key3: 'value3'

# Literal style
key4: |
  This is a literal style
  that preserves line breaks
    and indentation.
  
# Folded style
key5: >
  This is a folded style
  that combines multiple lines
  into a single line.