Prometheus support (#450)

Co-authored-by: nils måsén <nils@piksel.se>
Co-authored-by: MihailITPlace <ya.halo-halo@yandex.ru>
Co-authored-by: Sebastiaan Tammer <sebastiaantammer@gmail.com>

pkg/api/metrics/metrics.go

@@ -0,0 +1,27 @@
+package metrics
+
+import (
+	"github.com/containrrr/watchtower/pkg/metrics"
+	"net/http"
+
+	"github.com/prometheus/client_golang/prometheus/promhttp"
+)
+
+// Handler is an HTTP handle for serving metric data
+type Handler struct {
+	Path    string
+	Handle  http.HandlerFunc
+	Metrics *metrics.Metrics
+}
+
+// New is a factory function creating a new Metrics instance
+func New() *Handler {
+	m := metrics.Default()
+	handler := promhttp.Handler()
+
+	return &Handler{
+		Path:    "/v1/metrics",
+		Handle:  handler.ServeHTTP,
+		Metrics: m,
+	}
+}

pkg/api/metrics/metrics_test.go

@@ -0,0 +1,77 @@
+package metrics_test
+
+import (
+	"fmt"
+	"github.com/containrrr/watchtower/pkg/metrics"
+	"io/ioutil"
+	"net/http"
+	"testing"
+
+	"github.com/containrrr/watchtower/pkg/api"
+	metricsAPI "github.com/containrrr/watchtower/pkg/api/metrics"
+
+	. "github.com/onsi/ginkgo"
+	. "github.com/onsi/gomega"
+)
+
+const Token = "123123123"
+
+func TestContainer(t *testing.T) {
+	RegisterFailHandler(Fail)
+	RunSpecs(t, "Metrics Suite")
+}
+
+func runTestServer(m *metricsAPI.Handler) {
+	http.Handle(m.Path, m.Handle)
+	go func() {
+		http.ListenAndServe(":8080", nil)
+	}()
+}
+
+func getWithToken(c http.Client, url string) (*http.Response, error) {
+	req, _ := http.NewRequest("GET", url, nil)
+	req.Header.Add("Authorization", fmt.Sprintf("Bearer %s", Token))
+	return c.Do(req)
+}
+
+var _ = Describe("the metrics", func() {
+	httpAPI := api.New(Token)
+	m := metricsAPI.New()
+	httpAPI.RegisterHandler(m.Path, m.Handle)
+	httpAPI.Start(false)
+
+	// We should likely split this into multiple tests, but as prometheus requires a restart of the binary
+	// to reset the metrics and gauges, we'll just do it all at once.
+
+	It("should serve metrics", func() {
+		metric := &metrics.Metric{
+			Scanned: 4,
+			Updated: 3,
+			Failed:  1,
+		}
+		metrics.RegisterScan(metric)
+		c := http.Client{}
+		res, err := getWithToken(c, "http://localhost:8080/v1/metrics")
+
+		Expect(err).NotTo(HaveOccurred())
+		contents, err := ioutil.ReadAll(res.Body)
+		fmt.Printf("%s\n", string(contents))
+		Expect(string(contents)).To(ContainSubstring("watchtower_containers_updated 3"))
+		Expect(string(contents)).To(ContainSubstring("watchtower_containers_failed 1"))
+		Expect(string(contents)).To(ContainSubstring("watchtower_containers_scanned 4"))
+		Expect(string(contents)).To(ContainSubstring("watchtower_scans_total 1"))
+		Expect(string(contents)).To(ContainSubstring("watchtower_scans_skipped 0"))
+
+		for i := 0; i < 3; i++ {
+			metrics.RegisterScan(nil)
+		}
+
+		res, err = getWithToken(c, "http://localhost:8080/v1/metrics")
+		Expect(err).NotTo(HaveOccurred())
+		contents, err = ioutil.ReadAll(res.Body)
+		fmt.Printf("%s\n", string(contents))
+
+		Expect(string(contents)).To(ContainSubstring("watchtower_scans_total 4"))
+		Expect(string(contents)).To(ContainSubstring("watchtower_scans_skipped 3"))
+	})
+})