added dnscache

Dockerfile

@@ -1,9 +1,10 @@
 FROM golang:1.8
 
+RUN go get -u github.com/alecthomas/gometalinter && gometalinter --install
+
 WORKDIR /go/src/app
 COPY . .
 
-RUN go get -u github.com/alecthomas/gometalinter && gometalinter --install
 RUN go-wrapper download   # "go get -d -v ./..."
 RUN go-wrapper install    # "go install -v ./..."
 

README.md

@@ -82,6 +82,15 @@ To make sense of the detailed log messages when the application is handling lots
 
 To do the load testing I'm using [locust](http://locust.io), because it looks nice, I like Python, and I'm bored of [Gatling](http://gatling.io) (maybe just bored of apologising for Scala!)
 
+## DNS caching
+
+In my testing I found that some requests were timing out during DNS lookup.
+
+Since the application hits the same URL over and over again it seemed ridiculous to be doing the same DNS lookup repeatedly.
+
+Go does not cache DNS lookups by default - unlike, say, Java.
+
+I introduced [dnscache](https://github.com/viki-org/dnscache) and defined a custom Dial function when instantiating the http client in [app.go](app.go) - that got rid of all timeouts during the DNS lookup phase.
 
 
 

app.go

@@ -8,6 +8,8 @@ import (
 	"net/http"
 	"os"
 	"time"
+	"github.com/viki-org/dnscache"
+	"strings"
 )
 
 func main() {
@@ -21,9 +23,22 @@ func main() {
 
 	log.Info("Listening on", config.Port)
 
+	resolver := dnscache.New(time.Second * 60) //how often to refresh cached dns records, happens in background
+
 	httpClient := &http.Client{
 		Transport: &http.Transport{
 			MaxIdleConnsPerHost: config.HTTPClientMaxIdleConnsPerHost,
+			// Go does not cache DNS lookups, so we define a custom Dial function that does.
+			// This fixed a problem where requests were timing out during DNS lookup
+			// even though we were hitting the same hostname over and over.
+			Dial: func(network string, address string) (net.Conn, error) {
+				separator := strings.LastIndex(address, ":")
+				ip, err := resolver.FetchOneString(address[:separator])
+				if err != nil {
+					return nil, err
+				}
+				return net.Dial("tcp", ip + address[separator:])
+			},
 			DialContext: (&net.Dialer{
 				Timeout:   time.Duration(config.HTTPClientDialerTimeoutMS) * time.Millisecond,
 				KeepAlive: time.Duration(config.HTTPClientDialerKeepAliveMS) * time.Millisecond,

service.go

@@ -56,6 +56,10 @@ func (svc Service) Call(serviceRequest ServiceRequest) (serviceResponse ServiceR
 			"err":       err,
 			"requestid": serviceRequest.RequestID,
 		}).Error("Error parsing response from Service.")
+	} else {
+		log.WithFields(map[string]interface{}{
+			"requestid": serviceRequest.RequestID,
+		}).Info("Done with request")
 	}
 	return
 }

vendor/vendor.json

@@ -20,6 +20,12 @@
 			"revision": "89742aefa4b206dcf400792f3bd35b542998eb3b",
 			"revisionTime": "2017-08-22T13:27:46Z"
 		},
+		{
+			"checksumSHA1": "QITz/x1CJ8ylMdObGcdiL68xK8k=",
+			"path": "github.com/viki-org/dnscache",
+			"revision": "c70c1f23c5d84ab39054ec6b418a5ed0fa51cade",
+			"revisionTime": "2013-07-20T02:35:26Z"
+		},
 		{
 			"checksumSHA1": "nqWNlnMmVpt628zzvyo6Yv2CX5Q=",
 			"path": "golang.org/x/crypto/ssh/terminal",