I have a simple program below which is a simple HTTP client and server. I'm testing if MaxConnsPerHost in http.Transport introduced in Go 1.11 is working as advertised. However, when I run the code more than 10-30 minutes, the ESTABLISHED connections slowly exceeds the set MaxConnsPerHost. Am I doing something wrong?
package main
import (
"io/ioutil"
"log"
"net"
"net/http"
"time"
)
func main() {
// Server
//
go func() {
if err := http.ListenAndServe(":8081", http.HandlerFunc(
func(w http.ResponseWriter, r *http.Request) {
w.Write([]byte("hi"))
},
)); err != nil {
log.Fatal(err)
}
}()
// Client settings
//
c := &http.Client{
Timeout: 30 * time.Second,
Transport: &http.Transport{
Proxy: http.ProxyFromEnvironment,
DialContext: (&net.Dialer{
Timeout: 30 * time.Second,
KeepAlive: 30 * time.Second,
DualStack: true,
}).DialContext,
MaxIdleConns: 100,
IdleConnTimeout: 90 * time.Second,
TLSHandshakeTimeout: 10 * time.Second,
ExpectContinueTimeout: 1 * time.Second,
MaxConnsPerHost: 50,
},
}
// Worker loop
//
threads := 500
for i := 0; i < threads; i++ {
go func() {
for {
req, err := http.NewRequest("GET", "http://localhost:8081", nil)
if err != nil {
log.Fatal(err)
}
res, err := c.Do(req)
if err != nil {
log.Fatal(err)
}
if _, err := ioutil.ReadAll(res.Body); err != nil {
log.Fatal(err)
}
res.Body.Close()
}
}()
}
var done chan bool
<-done
log.Println("Done")
}
After running this for a long time, the ESTABLISHED connections reported by netstat is already exceeding 50.
P.S. We have an in issue in one of our services which horribly leaks ESTABLISHED connections even though we are properly closing the response's Body. It is currently built using Go 1.10 and I was hoping Go 1.11 MaxConnsPerHost would be a solution but it seems to also crack under heavy load.