Getting Started with cue

February 9, 2023

Install

go install cuelang.org/go/cmd/cue@latest

Generate a YAML file from cue

Prepare a sample file user.cue by a cue

import "time"

#User: {
    id: int
    name: string
    created: time.Format("2006-01-02")
}

john: #User
john: {
    id: 1
    name: "John"
    created: "2023-02-09"
}

Then run a command to output a yaml file by the export subcommand.

> cue export user.cue --out yaml
john:
  id: 1
  name: John
  created: "2023-02-09"

Use Go packages

Use Go packages like k8s definitions, by following this and this documents.

go mod init github.com/at-ishikawa/at-ishikawa.github.com/examples/cue/go
go get k8s.io/api/core/v1
cue get go k8s.io/api/core/v1

Now then you can see the files like

> ls
cue.mod/ go.mod   go.sum

Now, let’s make a file to create k8s service definitions by cue. Let’s say it’s defined in service.cue

import "k8s.io/api/core/v1"

services: [string]: v1.#Service

services: {
    http: {
        // Next is shows an error
        // unknown: "name"
        apiVersion: "v1"
        kind: "Service"
        metadata: {
            name: "http-service"
            namespace: "app"
        }
        spec: {
            selector: {
                "app.kubernetes.io/name": "app"
            }
            ports: [
                {
                    protocol: "TCP"
                    port: 80
                    targetPort: 80
                }
            ]
        }
    }
}

Then you can export the yaml file for the kubernetes service http-service by

cue export service.cue --out yaml -e 'services.http'

Last updated on January 25, 2025

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