least-connected load-balancing, per-host rate-limiting & load from config

config.go

@@ -0,0 +1,53 @@
+package main
+
+import (
+	"encoding/json"
+	"golang.org/x/time/rate"
+	"io/ioutil"
+	"os"
+	"time"
+)
+
+type HostConfig struct {
+	Every   string            `json:"every"`
+	Burst   int               `json:"burst"`
+	Headers map[string]string `json:"headers"`
+}
+
+type ProxyConfig struct {
+	Name string `json:"name"`
+	Url  string `json:"url"`
+}
+
+var config struct {
+	Addr    string                `json:"addr"`
+	Hosts   map[string]HostConfig `json:"hosts"`
+	Proxies []ProxyConfig         `json:"proxies"`
+}
+
+func loadConfig() {
+
+	configFile, err := os.Open("config.json")
+	handleErr(err)
+
+	configBytes, err := ioutil.ReadAll(configFile)
+	handleErr(err)
+
+	err = json.Unmarshal(configBytes, &config)
+	handleErr(err)
+}
+
+func applyConfig(proxy *Proxy) {
+
+	for host, conf := range config.Hosts {
+		duration, err := time.ParseDuration(conf.Every)
+		handleErr(err)
+		proxy.Limiters.Store(host, rate.NewLimiter(rate.Every(duration), conf.Burst))
+	}
+}
+
+func handleErr(err error) {
+	if err != nil {
+		panic(err)
+	}
+}

config.json

@@ -0,0 +1,25 @@
+{
+  "addr": "localhost:5050",
+  "proxies": [
+    {
+      "name": "p0",
+      "url": ""
+    },
+    {
+      "name": "p1",
+      "url": "http://localhost:3128"
+    }
+  ],
+  "hosts": {
+    "*": {
+      "every": "10s",
+      "burst": 1,
+      "headers": {}
+    },
+    "reddit.com": {
+      "every": "100s",
+      "burst": 1,
+      "headers": {}
+    }
+  }
+}

main.go

@@ -7,6 +7,7 @@ import (
 	"golang.org/x/time/rate"
 	"net/http"
 	"net/url"
+	"sort"
 	"strings"
 	"sync"
 	"time"
@@ -22,6 +23,21 @@ type Proxy struct {
 	Url         *url.URL
 	Limiters    sync.Map
 	HttpClient  *http.Client
+	Connections int
+}
+
+type ByConnectionCount []*Proxy
+
+func (a ByConnectionCount) Len() int {
+	return len(a)
+}
+
+func (a ByConnectionCount) Swap(i, j int) {
+	a[i], a[j] = a[j], a[i]
+}
+
+func (a ByConnectionCount) Less(i, j int) bool {
+	return a[i].Connections < a[j].Connections
 }
 
 func LogRequestMiddleware(h goproxy.FuncReqHandler) goproxy.ReqHandler {
@@ -41,8 +57,8 @@ func (p *Proxy) getLimiter(host string) *rate.Limiter {
 	limiter, ok := p.Limiters.Load(host)
 	if !ok {
 
-		every, _ := time.ParseDuration("100ms")
-		limiter = rate.NewLimiter(rate.Every(every), 0)
+		every, _ := time.ParseDuration("1ms")
+		limiter = rate.NewLimiter(rate.Every(every), 1)
 		p.Limiters.Store(host, limiter)
 
 		logrus.WithFields(logrus.Fields{
@@ -65,6 +81,8 @@ func (b *Balancer) chooseProxy(host string) *Proxy {
 
 	_ = simplifyHost(host)
 
+	sort.Sort(ByConnectionCount(b.proxies))
+
 	return b.proxies[0]
 }
 
@@ -79,14 +97,31 @@ func New() *Balancer {
 	balancer.server.OnRequest().Do(LogRequestMiddleware(
 		func(r *http.Request, ctx *goproxy.ProxyCtx) (*http.Request, *http.Response) {
 
-			p := balancer.chooseProxy(r.Host)
+			sHost := simplifyHost(r.Host)
+			p := balancer.chooseProxy(sHost)
 
+			p.Connections += 1
 			logrus.WithFields(logrus.Fields{
 				"proxy":      p.Name,
+				"connexions": p.Connections,
 			}).Trace("Routing request")
 
+			limiter := p.getLimiter(sHost)
+			reservation := limiter.Reserve()
+			if !reservation.OK() {
+				logrus.Warn("Could not reserve")
+			}
+			delay := reservation.Delay()
+			if delay > 0 {
+				logrus.WithFields(logrus.Fields{
+					"time": delay,
+				}).Trace("Sleeping")
+				time.Sleep(delay)
+			}
+
 			proxyReq := preprocessRequest(cloneRequest(r))
 			resp, err := p.HttpClient.Do(proxyReq)
+			p.Connections -= 1
 
 			//TODO: handle err
 			if err != nil {
@@ -166,12 +201,21 @@ func NewProxy(name, stringUrl string) (*Proxy, error) {
 func main() {
 	logrus.SetLevel(logrus.TraceLevel)
 
+	loadConfig()
 	balancer := New()
 
-	p0, _ := NewProxy("p0", "http://localhost:3128")
-	//p0, _ := NewProxy("p0", "")
+	for _, proxyConf := range config.Proxies {
+		proxy, err := NewProxy(proxyConf.Name, proxyConf.Url)
+		handleErr(err)
+		balancer.proxies = append(balancer.proxies, proxy)
 
-	balancer.proxies = []*Proxy{p0}
+		applyConfig(proxy)
+
+		logrus.WithFields(logrus.Fields{
+			"name": proxy.Name,
+			"url":  proxy.Url,
+		}).Info("Proxy")
+	}
 
 	balancer.Run()
 }

web.py

@@ -0,0 +1,14 @@
+from flask import Flask
+import time
+
+app = Flask(__name__)
+
+
+@app.route("/")
+def hello():
+    time.sleep(3)
+    return "Hello World!"
+
+
+if __name__ == "__main__":
+    app.run(port=9999)