How-to write a Charm

Create a new directory for your charm project and initialize a Go module. Here the charm name is example, replace it with your desired charm name:

mkdir example
cd example
go mod init example

Create a cmd/example/main.go file with the following content:

package main

import (
    "os"

    "example/internal/charm"

    "github.com/gruyaume/goops"
)

func main() {
    env := goops.ReadEnv()

    goops.LogInfof("Hook name: %s", env.HookName)

    err := charm.Configure()
    if err != nil {
        goops.LogErrorf("Error handling hook: %s", err.Error())
        os.Exit(1)
    }
}

Create a internal/charm/charm.go file with the charm logic. For example:

package charm

import (
    "fmt"

    "github.com/gruyaume/goops"
)

type Config struct {
    Username string `json:"username"`
}

func Configure() error {
    isLeader, err := goops.IsLeader()
    if err != nil {
        return fmt.Errorf("could not check if unit is leader: %w", err)
    }

    if !isLeader {
        err := goops.SetUnitStatus(goops.StatusBlocked, "Unit is not leader")
        if err != nil {
            return fmt.Errorf("could not set unit status: %w", err)
        }
        return nil
    }

    goops.LogInfof("Unit is leader")

    var config Config
    err = goops.GetConfig(&config)
    if err != nil {
        return fmt.Errorf("could not get config: %w", err)
    }

    if config.Username == "" {
        err := goops.SetUnitStatus(goops.StatusBlocked, "Username is not set in config")
        if err != nil {
            return fmt.Errorf("could not set unit status: %w", err)
        }
        return nil
    }

    err = goops.SetUnitStatus(goops.StatusActive, fmt.Sprintf("Username is set to '%s'", config.Username))
    if err != nil {
        return fmt.Errorf("could not set unit status: %w", err)
    }

    return nil
}

Install go dependencies:

go mod tidy