Add page operation metrics and expose them in Prometheus text format.

src/config.go

@@ -45,9 +45,10 @@ type Config struct {
 }
 
 type ServerConfig struct {
-	Pages  string `toml:"pages" default:"tcp/:3000"`
-	Caddy  string `toml:"caddy" default:"tcp/:3001"`
-	Health string `toml:"health" default:"tcp/:3002"`
+	Pages   string `toml:"pages" default:"tcp/:3000"`
+	Caddy   string `toml:"caddy" default:"tcp/:3001"`
+	Health  string `toml:"health" default:"tcp/:3002"`
+	Metrics string `toml:"metrics" default:"tcp/:3003"`
 }
 
 type WildcardConfig struct {

src/main.go

@@ -50,10 +50,8 @@ func panicHandler(handler http.Handler) http.Handler {
 	})
 }
 
-func serve(listener net.Listener, serve func(http.ResponseWriter, *http.Request)) {
+func serve(listener net.Listener, handler http.Handler) {
 	if listener != nil {
-		var handler http.Handler
-		handler = http.HandlerFunc(serve)
 		handler = ObserveHTTPHandler(handler)
 		handler = panicHandler(handler)
 
@@ -148,6 +146,7 @@ func main() {
 		pagesListener := listen("pages", config.Server.Pages)
 		caddyListener := listen("caddy", config.Server.Caddy)
 		healthListener := listen("health", config.Server.Health)
+		metricsListener := listen("metrics", config.Server.Metrics)
 
 		if err := ConfigureBackend(&config.Storage); err != nil {
 			log.Fatalln(err)
@@ -157,9 +156,10 @@ func main() {
 			log.Fatalln(err)
 		}
 
-		go serve(pagesListener, ServePages)
-		go serve(caddyListener, ServeCaddy)
-		go serve(healthListener, ServeHealth)
+		go serve(pagesListener, http.HandlerFunc(ServePages))
+		go serve(caddyListener, http.HandlerFunc(ServeCaddy))
+		go serve(healthListener, http.HandlerFunc(ServeHealth))
+		go serve(metricsListener, NewMetricsHTTPHandler())
 
 		if config.Insecure {
 			log.Println("serve: ready (INSECURE)")

src/observe.go

@@ -6,6 +6,7 @@ import (
 	"runtime/debug"
 
 	"github.com/honeybadger-io/honeybadger-go"
+	"github.com/prometheus/client_golang/prometheus/promhttp"
 )
 
 func hasHoneybadger() bool {
@@ -25,3 +26,7 @@ func ObserveHTTPHandler(handler http.Handler) http.Handler {
 	}
 	return handler
 }
+
+func NewMetricsHTTPHandler() http.Handler {
+	return promhttp.Handler()
+}

src/pages.go

@@ -14,14 +14,51 @@ import (
 	"path"
 	"strings"
 	"time"
+
+	"github.com/prometheus/client_golang/prometheus"
+	"github.com/prometheus/client_golang/prometheus/promauto"
 )
 
 const notFoundPage = "404.html"
 
+var (
+	siteUpdatesCount = promauto.NewCounterVec(prometheus.CounterOpts{
+		Name: "git_pages_site_updates",
+		Help: "Count of site updates in total",
+	}, []string{"via"})
+	siteUpdateOkCount = promauto.NewCounterVec(prometheus.CounterOpts{
+		Name: "git_pages_site_update_ok",
+		Help: "Count of successful site updates",
+	}, []string{"outcome"})
+	siteUpdateErrorCount = promauto.NewCounterVec(prometheus.CounterOpts{
+		Name: "git_pages_site_update_error",
+		Help: "Count of failed site updates",
+	}, []string{"cause"})
+)
+
 func makeWebRoot(host string, projectName string) string {
 	return fmt.Sprintf("%s/%s", strings.ToLower(host), projectName)
 }
 
+func reportSiteUpdate(via string, result *UpdateResult) {
+	siteUpdatesCount.With(prometheus.Labels{"via": via}).Inc()
+
+	switch result.outcome {
+	case UpdateError:
+		siteUpdateErrorCount.With(prometheus.Labels{"cause": "other"}).Inc()
+	case UpdateTimeout:
+		siteUpdateErrorCount.With(prometheus.Labels{"cause": "timeout"}).Inc()
+	case UpdateNoChange:
+		// nothing to report
+	case UpdateCreated:
+		siteUpdateOkCount.With(prometheus.Labels{"outcome": "created"}).Inc()
+	case UpdateReplaced:
+		siteUpdateOkCount.With(prometheus.Labels{"outcome": "replaced"}).Inc()
+	case UpdateDeleted:
+		siteUpdateOkCount.With(prometheus.Labels{"outcome": "deleted"}).Inc()
+	}
+}
+
 func getPage(w http.ResponseWriter, r *http.Request) error {
 	var err error
 	var sitePath string
@@ -266,6 +303,7 @@ func putPage(w http.ResponseWriter, r *http.Request) error {
 	} else {
 		fmt.Fprintln(w, "internal error")
 	}
+	reportSiteUpdate("rest", &result)
 	return nil
 }
 
@@ -401,6 +439,7 @@ func postPage(w http.ResponseWriter, r *http.Request) error {
 			fmt.Fprintf(w, "- %s\n", problem)
 		}
 	}
+	reportSiteUpdate("webhook", &result)
 	return nil
 }