automation

Automation with KCL

Prerequisite

• Firstly, download and install KCL according to the instructions, and then prepare a Kubernetes environment.

1. Show Config

We can run the following command to show the config.

cat main.k

The output is

schema App:
    """The application model."""
    name: str
    replicas: int
    labels?: {str:str} = {app = name}

app: App {
    name = "app"
    replicas = 1
    labels.key = "value"
}

We can run the command to get the config

kcl main.k

The output is

app:
  name: app
  replicas: 1
  labels:
    app: app
    key: value

2. Use KCL CLI for Automation

KCL allows us to directly modify the values in the configuration model through the KCL CLI -O|--overrides parameter. The parameter contains three parts e.g., pkg, identifier, attribute and override_value.

kcl main.k -O override_spec

• override_spec represents a unified representation of the configuration model fields and values that need to be modified

override_spec: [[pkgpath] ":"] identifier ("=" value | "-")

• pkgpath: indicates the package path where the identifier needs to be modified, usually in the form of a.b.c. For the main package,pkgpath is represented as __ main__. When omitted or not written, it indicates the main package
• identifier indicates the identifier that needs to modify the configuration, usually in the form of a.b.c.
• value indicates the value of the configuration that needs to be modified, which can be any legal KCL expression, such as number/string literal value, list/dict/schema expression, etc.
• = denotes modifying of the value of the identifier.
• - denotes deleting of the identifier.

Override Configuration

Run the command to update the application name.

kcl main.k -O app.name='new_app'

The output is

app:
  name: new_app
  replicas: 1
  labels:
    app: new_app
    key: value

We can see the name attribute of the app config is updated to new_app.

Besides, when we use KCL CLI -d argument, the KCL file will be modified to the following content at the same time.

kcl main.k -O app.name='new_app' -d

schema App:
    """The application model."""
    name: str
    replicas: int
    labels?: {str:str} = {app = name}

app: App {
    name = "new_app"
    replicas = 1
    labels: {key = "value"}
}

Delete Configuration

Run the command to delete the key attribute of labels.

kcl main.k -O app.labels.key-

The output is

app:
  name: app
  replicas: 1
  labels:
    app: app