Fast start the dns resolution ticker to improve first report latency.

probe/appclient/app_client.go

@@ -4,6 +4,7 @@ import (
 	"fmt"
 	"io"
 	"io/ioutil"
+	"net"
 	"net/http"
 	"net/rpc"
 	"sync"
@@ -20,6 +21,7 @@ import (
 const (
 	initialBackoff = 1 * time.Second
 	maxBackoff     = 60 * time.Second
+	dialTimeout    = 5 * time.Second
 )
 
 // AppClient is a client to an app for dealing with controls.
@@ -64,6 +66,10 @@ func NewAppClient(pc ProbeConfig, hostname, target string, control xfer.ControlH
 		return nil, err
 	}
 
+	httpTransport.Dial = func(network, addr string) (net.Conn, error) {
+		return net.DialTimeout(network, addr, dialTimeout)
+	}
+
 	return &appClient{
 		ProbeConfig: pc,
 		quit:        make(chan struct{}),

probe/appclient/resolver.go

@@ -17,9 +17,30 @@ const (
 )
 
 var (
-	tick = time.Tick
+	tick = fastStartTicker
 )
 
+// fastStartTicker is a ticker that 'ramps up' from 1 sec to duration.
+func fastStartTicker(duration time.Duration) <-chan time.Time {
+	c := make(chan time.Time, 1)
+	go func() {
+		d := 1 * time.Second
+		for {
+			time.Sleep(d)
+			d = d * 2
+			if d > duration {
+				d = duration
+			}
+
+			select {
+			case c <- time.Now():
+			default:
+			}
+		}
+	}()
+	return c
+}
+
 type setter func(string, []string)
 
 // Resolver is a thing that can be stopped...