client.go

package main

import (
	"errors"
	"io"
	"log"
	"net/http"
	"time"

	"github.com/sony/gobreaker"
)

func main() {
	cbs := gobreaker.Settings{
		Name:     "cl",
		Interval: 5 * time.Second,
		Timeout:  7 * time.Second,
		ReadyToTrip: func(counts gobreaker.Counts) bool {
			failureRatio := float64(counts.TotalFailures) / float64(counts.Requests)
			result := counts.Requests >= 3 && failureRatio >= 0.6
			return result
		},
		OnStateChange: func(_ string, from gobreaker.State, to gobreaker.State) {
			// Handler for every state change. We'll use for debugging purpose
			log.Println("state changed from", from.String(), "to", to.String())
		},
	}

	cb := gobreaker.NewCircuitBreaker(cbs)

	for {
		time.Sleep(1 * time.Second)
		get(cb)
	}

}

func get(cb *gobreaker.CircuitBreaker) {

	_, err := cb.Execute(func() (interface{}, error) {
		response, err := http.Get("http://localhost:8082/hello")
		if err != nil {
			return nil, err
		}
		defer response.Body.Close()

		log.Println(response.Status)

		dataByte, err := io.ReadAll(response.Body)
		if err != nil {
			return nil, err
		}

		log.Println(string(dataByte))
		if response.StatusCode == http.StatusInternalServerError {
			return nil, errors.New("internal server error")
		}
		return dataByte, nil
	})
	if err != nil {
		log.Println("error cb", err)
		return
	}
}

server.go

package main

import (
	"fmt"
	"log"
	"net/http"
)

var isSuccess bool = true

func main() {
	http.HandleFunc("/hello", func(w http.ResponseWriter, r *http.Request) {
		log.Println("receive request")
		if isSuccess {
			w.WriteHeader(http.StatusOK)
			w.Write([]byte("success response"))
		} else {
			w.WriteHeader(http.StatusInternalServerError)
			w.Write([]byte("fail response"))
		}

	})

	http.HandleFunc("/toggle", func(w http.ResponseWriter, r *http.Request) {
		if isSuccess {
			fmt.Println("success change to false")
			isSuccess = false
		} else {
			fmt.Println("success change to true")
			isSuccess = true
		}
	})
	http.ListenAndServe("localhost:8082", nil)
}