Adds basic Prometheus support

imageproxy.go

@@ -32,6 +32,7 @@ import (
 	"time"
 
 	"github.com/gregjones/httpcache"
+	"github.com/prometheus/client_golang/prometheus/promhttp"
 	tphttp "willnorris.com/go/imageproxy/third_party/http"
 )
 
@@ -115,11 +116,19 @@ func (p *Proxy) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
+	if r.URL.Path == "/metrics" {
+		var h http.Handler = promhttp.Handler()
+		h.ServeHTTP(w, r)
+		return
+	}
+
 	var h http.Handler = http.HandlerFunc(p.serveImage)
 	if p.Timeout > 0 {
 		h = tphttp.TimeoutHandler(h, p.Timeout, "Gateway timeout waiting for remote resource.")
 	}
+	start := time.Now()
 	h.ServeHTTP(w, r)
+	httpRequestsResponseTime.Observe(float64(time.Since(start).Seconds()))
 }
 
 // serveImage handles incoming requests for proxied images.
@@ -146,6 +155,7 @@ func (p *Proxy) serveImage(w http.ResponseWriter, r *http.Request) {
 		msg := fmt.Sprintf("error fetching remote image: %v", err)
 		log.Print(msg)
 		http.Error(w, msg, http.StatusInternalServerError)
+		remoteImageFetchErrors.Inc()
 		return
 	}
 	defer resp.Body.Close()
@@ -155,6 +165,10 @@ func (p *Proxy) serveImage(w http.ResponseWriter, r *http.Request) {
 		log.Printf("request: %v (served from cache: %v)", *req, cached == "1")
 	}
 
+	if cached == "1" {
+		requestServedFromCacheCount.Inc()
+	}
+
 	copyHeader(w.Header(), resp.Header, "Cache-Control", "Last-Modified", "Expires", "Etag", "Link")
 
 	if should304(r, resp) {

metrics.go

@@ -0,0 +1,33 @@
+package imageproxy
+
+import (
+	"github.com/prometheus/client_golang/prometheus"
+)
+
+var (
+	requestServedFromCacheCount = prometheus.NewCounter(
+		prometheus.CounterOpts{
+			Name: "requests_served_from_cache",
+			Help: "Number of requests served from cache.",
+		})
+	imageTransformationSummary = prometheus.NewSummary(prometheus.SummaryOpts{
+		Name: "image_transformation_seconds",
+		Help: "Time taken for image transformations in seconds.",
+	})
+	remoteImageFetchErrors = prometheus.NewCounter(prometheus.CounterOpts{
+		Name: "remote_image_fetch_errors",
+		Help: "Total image fetch failures",
+	})
+	httpRequestsResponseTime = prometheus.NewSummary(prometheus.SummaryOpts{
+		Namespace: "http",
+		Name:      "response_time_seconds",
+		Help:      "Request response times",
+	})
+)
+
+func init() {
+	prometheus.MustRegister(imageTransformationSummary)
+	prometheus.MustRegister(requestServedFromCacheCount)
+	prometheus.MustRegister(remoteImageFetchErrors)
+	prometheus.MustRegister(httpRequestsResponseTime)
+}

transform.go

@@ -24,6 +24,7 @@ import (
 	"io"
 	"log"
 	"math"
+	"time"
 
 	"github.com/disintegration/imaging"
 	"github.com/muesli/smartcrop"
@@ -269,6 +270,7 @@ func transformImage(m image.Image, opt Options) image.Image {
 	// Parse crop and resize parameters before applying any transforms.
 	// This is to ensure that any percentage-based values are based off the
 	// size of the original image.
+	start := time.Now()
 	rect := cropParams(m, opt)
 	w, h, resize := resizeParams(m, opt)
 
@@ -308,5 +310,6 @@ func transformImage(m image.Image, opt Options) image.Image {
 		m = imaging.FlipH(m)
 	}
 
+	imageTransformationSummary.Observe(float64(time.Since(start).Seconds()))
 	return m
 }