Make client a service with configurable registration -interval (#22)

* Turn autojoin client into a service with configurable -interval

* Remove unnecessary fmt

* Don't spawn a goroutine

* Use memoryless

cmd/register/main.go

@@ -1,16 +1,19 @@
 package main
 
 import (
+	"context"
 	"encoding/json"
 	"flag"
-	"fmt"
 	"io"
+	"log"
 	"net/http"
 	"net/url"
 	"os"
 	"path"
+	"time"
 
 	v0 "github.com/m-lab/autojoin/api/v0"
+	"github.com/m-lab/go/memoryless"
 	"github.com/m-lab/go/rtx"
 	v2 "github.com/m-lab/locate/api/v2"
 	"github.com/m-lab/uuid-annotator/annotator"
@@ -24,14 +27,17 @@ const (
 )
 
 var (
-	endpoint   = flag.String("endpoint", registerEndpoint, "Endpoint of the autojoin service")
-	apiKey     = flag.String("key", "", "API key for the autojoin service")
-	service    = flag.String("service", "ndt", "Service name to register with the autojoin service")
-	org        = flag.String("organization", "", "Organization to register with the autojoin service")
-	iata       = flag.String("iata", "", "IATA code to register with the autojoin service")
-	ipv4       = flag.String("ipv4", "", "IPv4 address to register with the autojoin service")
-	ipv6       = flag.String("ipv6", "", "IPv6 address to register with the autojoin service")
-	outputPath = flag.String("output", "", "Output folder")
+	endpoint    = flag.String("endpoint", registerEndpoint, "Endpoint of the autojoin service")
+	apiKey      = flag.String("key", "", "API key for the autojoin service")
+	service     = flag.String("service", "ndt", "Service name to register with the autojoin service")
+	org         = flag.String("organization", "", "Organization to register with the autojoin service")
+	iata        = flag.String("iata", "", "IATA code to register with the autojoin service")
+	ipv4        = flag.String("ipv4", "", "IPv4 address to register with the autojoin service")
+	ipv6        = flag.String("ipv6", "", "IPv6 address to register with the autojoin service")
+	interval    = flag.Duration("interval.expected", 1*time.Hour, "Expected registration interval")
+	intervalMin = flag.Duration("interval.min", 55*time.Minute, "Minimum registration interval")
+	intervalMax = flag.Duration("interval.max", 65*time.Minute, "Maximum registration interval")
+	outputPath  = flag.String("output", "", "Output folder")
 )
 
 func main() {
@@ -41,6 +47,25 @@ func main() {
 		panic("-key, -service, -organization, and -iata are required.")
 	}
 
+	register()
+
+	// Keep retrying registration every configured interval.
+	t, err := memoryless.NewTicker(context.Background(), memoryless.Config{
+		Expected: *interval,
+		Min:      *intervalMin,
+		Max:      *intervalMax,
+	})
+	rtx.Must(err, "Failed to create ticker")
+
+	for range t.C {
+		register()
+	}
+}
+
+// Make a call to the register endpoint and write the resulting config files to
+// disk. If the node is registered already, this is effectively a no-op for the
+// autojoin API and will just touch the output files' last-modified time.
+func register() {
 	// Make a HTTP call to the autojoin service to register this node.
 	registerURL, err := url.Parse(*endpoint)
 	rtx.Must(err, "Failed to parse autojoin service URL")
@@ -53,12 +78,13 @@ func main() {
 	q.Add("ipv6", *ipv6)
 	registerURL.RawQuery = q.Encode()
 
+	log.Printf("Registering with %s", registerURL)
+
 	resp, err := http.Post(registerURL.String(), "application/json", nil)
 	rtx.Must(err, "POST autojoin/v0/node/register failed")
 	defer resp.Body.Close()
 
 	if resp.StatusCode != http.StatusOK {
-		fmt.Println(resp.Status)
 		panic("Failed to register with autojoin service")
 	}
 
@@ -88,4 +114,6 @@ func main() {
 	rtx.Must(err, "Failed to write heartbeat file")
 	err = os.WriteFile(path.Join(*outputPath, annotationFilename), annotationJSON, 0644)
 	rtx.Must(err, "Failed to write annotation file")
+
+	log.Printf("Registration successful with hostname: %s", r.Registration.Hostname)
 }