What is a YAML file?

A YAML file is used to represent data, in case of Kubernetes it is configuration data. The other formats in which data can be represented are XML and JSON.

In this article I will explain you about the different elements types for the YAML files.

In YAML files, key-value pairs are used to define attributes and settings for various data structures.

There are different types of key-value pairs that can exist in YAML files, depending on the context and the type of data being represented.

Here are the common types of key-value pairs you may encounter:

1. Scalar Key-Value Pair:
   This is the most basic type of key-value pair, where a single value is associated with a specific key. The value can be a string, number, boolean, or null.

Remember that you need to have a space between the colon and value.

  key: value

Example:

   name: John Doe
   age: 30
   is_active: true

1. Mapping Key-Value Pair or Dictionary:
   A mapping key-value pair is used to associate a key with another nested data structure, such as another key-value pair, a list, or another mapping.

   key:
     nested_key: nested_value

As you can see in the example below, the name, age and address are the properties of the person. But address is another mapping key with sub properties such as city and country.

Example:

   person:
     name: John Doe
     age: 30
     address:
       city: New York
       country: USA

1. List Key-Value Pair:
   Lists in YAML represent sequences of values and are denoted by a hyphen followed by a space (“- “). Lists can contain various data types, including strings, numbers, booleans, and other lists.

The “-” represents that it is an elements of an array.

   key:
     - value1
     - value2
     - value3

Example:

   fruits:
     - apple
     - orange
     - banana
   vegetables:
     - Carrot
     - Ladyfinger
     - Potato

Kubernetes YAML file

• A Kubernetes YAML file contains four top-level properties: apiVersion, kind, metadata, and spec.
• apiVersion specifies the version of the Kubernetes API to use.
• kind specifies the type of Kubernetes object being defined.
• metadata contains information about the object such as its name.
• spec contains the desired state of the object.

Here is an example of a Kubernetes YAML file defining a deployment:

apiVersion: apps/v1
kind: Deployment
metadata:
  name: nginx-deployment
spec:
  replicas: 3
  selector:
    matchLabels:
      app: nginx
  template:
    metadata:
      labels:
        app: nginx
    spec:
      containers:
      - name: nginx
        image: nginx:1.14.2
        ports:
        - containerPort: 80

In this example, apiVersion is set to apps/v1 to use the apps API group, kind is set to Deployment to define a deployment object, metadata specifies the name of the deployment as nginx-deployment, and spec specifies that there should be 3 replicas of the deployment, each running the nginx:1.14.2 container image and exposing port 80.

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