feat(metrics): wire instrumentation through queue, handlers, middleware

internal/api/handlers.go

@@ -8,6 +8,7 @@ import (
 	"github.com/docker/docker/api/types"
 	"github.com/shcizo/package-updater/internal/discovery"
 	"github.com/shcizo/package-updater/internal/logging"
+	"github.com/shcizo/package-updater/internal/metrics"
 	"github.com/shcizo/package-updater/internal/updater"
 )
 
@@ -34,11 +35,13 @@ type Handlers struct {
 	version   string
 	commit    string
 	buildTime string
+	metrics   *metrics.Metrics
 }
 
 // NewHandlers constructs a Handlers value with all dependencies injected.
-func NewHandlers(f Finder, s Submitter, p Pinger, version, commit, buildTime string) *Handlers {
-	return &Handlers{finder: f, submitter: s, pinger: p, version: version, commit: commit, buildTime: buildTime}
+// m may be nil, in which case metrics recording is silently skipped.
+func NewHandlers(f Finder, s Submitter, p Pinger, version, commit, buildTime string, m *metrics.Metrics) *Handlers {
+	return &Handlers{finder: f, submitter: s, pinger: p, version: version, commit: commit, buildTime: buildTime, metrics: m}
 }
 
 // Update implements POST /update.
@@ -107,9 +110,15 @@ func (h *Handlers) Update(w http.ResponseWriter, r *http.Request) {
 // Healthz implements GET /healthz.
 func (h *Handlers) Healthz(w http.ResponseWriter, r *http.Request) {
 	if _, err := h.pinger.Ping(r.Context()); err != nil {
+		if h.metrics != nil {
+			h.metrics.DockerPingUp.Set(0)
+		}
 		writeJSON(w, http.StatusServiceUnavailable, HealthResponse{Status: "unhealthy", Docker: "unreachable"})
 		return
 	}
+	if h.metrics != nil {
+		h.metrics.DockerPingUp.Set(1)
+	}
 	writeJSON(w, http.StatusOK, HealthResponse{Status: "ok", Docker: "ok"})
 }