service_registry.go

package main

import (
	"encoding/json"
	"fmt"
)

type ServiceDescriptionPayload struct {
	Address string `json:"address"`
}
type ServiceDescription struct {
	Action  string                    `json:"action"`
	Payload ServiceDescriptionPayload `json:"payload"`
}

func main() {
	publicIP := "8.8.8.8"
	serviceDescription, err := json.Marshal(ServiceDescription{
		Action: "write",
		Payload: ServiceDescriptionPayload{
			Address: publicIP,
		},
	})
	if err != nil {
		// ...
	}
	fmt.Println(serviceDescription)
}