Go LoadBalancer

Require Go 1.21+.

Install

$ go get -u github.com/xgfone/go-loadbalancer

Example

Mini API Gateway

package main

import (
	"encoding/json"
	"flag"
	"net/http"

	"github.com/xgfone/go-loadbalancer"
	"github.com/xgfone/go-loadbalancer/balancer"
	"github.com/xgfone/go-loadbalancer/forwarder"
	"github.com/xgfone/go-loadbalancer/httpx"
)

var listenAddr = flag.String("listenaddr", ":80", "The address that api gateway listens on.")

func main() {
	flag.Parse()
	http.HandleFunc("/admin/route", registerRouteHandler)
	_ = http.ListenAndServe(*listenAddr, nil)
}

func registerRouteHandler(w http.ResponseWriter, r *http.Request) {
	if r.Method != http.MethodPost {
		w.WriteHeader(http.StatusMethodNotAllowed)
		return
	}

	var req struct {
		// Route Matcher
		Path   string `json:"path" validate:"required"`
		Method string `json:"method" validate:"required"`

		// Upstream Endpoints
		Upstream struct {
			ForwardPolicy string `json:"forwardPolicy" default:"weight_random"`
			Servers       []struct {
				Host   string `json:"host" validate:"host"`
				Port   uint16 `json:"port" validate:"ranger(1,65535)"`
				Weight int    `json:"weight" default:"1" validate:"min(1)"`
			} `json:"servers"`
		} `json:"upstream"`
	}

	// Notice: here we don't validate whether the values are valid.
	if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
		http.Error(w, "invalid request route paramenter: "+err.Error(), 400)
		return
	}

	// Build the upstream backend servers.
	static := loadbalancer.NewStaticWithCap(len(req.Upstream.Servers))
	for _, server := range req.Upstream.Servers {
		c := httpx.Config{Host: server.Host, Port: server.Port, Weight: server.Weight}
		static.Append(c.NewEndpoint())
	}

	// Build the loadbalancer forwarder.
	balancer := balancer.Get(req.Upstream.ForwardPolicy) // not check it is nil
	forwarder := forwarder.New(req.Method+"@"+req.Path, balancer, static)

	// Register the route and forward the request to forwarder.
	http.HandleFunc(req.Path, func(w http.ResponseWriter, r *http.Request) {
		if r.Method != req.Method {
			w.WriteHeader(http.StatusMethodNotAllowed)
		} else {
			// You can use forwarder.ForwardHTTP to control the request and response.
			forwarder.ServeHTTP(w, r)
		}
	})
}

# Run the mini API-Gateway on the host 192.168.1.10
$ nohup go run main.go &

# Add the route
# Notice: remove the characters from // to the line end.
$ curl -XPOST http://127.0.0.1/admin/route -H 'Content-Type: application/json' -d '
{
    "path": "/path",
    "method": "GET",
    "upstream": {
        "forwardPolicy": "weight_round_robin",
        "servers": [
            {"host": "192.168.1.11", "port": 80, "weight": 10}, // 33.3% requests
            {"host": "192.168.1.12", "port": 80, "weight": 20}  // 66.7% requests
        ]
    }
}'

# Access the backend servers by the mini API-Gateway:
# 2/6(33.3%) requests -> 192.168.1.11
# 4/6(66.7%) requests -> 192.168.1.12
$ curl http://192.168.1.10/path
192.168.1.11/backend/path

$ curl http://192.168.1.10/path
192.168.1.12/backend/path

$ curl http://192.168.1.10/path
192.168.1.12/backend/path

$ curl http://192.168.1.10/path
192.168.1.11/backend/path

$ curl http://192.168.1.10/path
192.168.1.12/backend/path

$ curl http://192.168.1.10/path
192.168.1.12/backend/path