feat: healthz server (#3228)

* feat: healthz server

Signed-off-by: Asgeir Nilsen <asgeir@twingine.no>

* fix: startup and readiness probe activation points

Enable startup probe at end of Controller.Init and readiness probe at
end of Controller.Run

Signed-off-by: Asgeir Nilsen <asgeir@twingine.no>

* fix: rewrote to reuse same HTTP listener

Signed-off-by: Asgeir Nilsen <asgeir@twingine.no>

---------

Signed-off-by: Asgeir Nilsen <asgeir@twingine.no>

pkg/common/healthz.go

@@ -0,0 +1,64 @@
+package common
+
+import (
+	"errors"
+	"net/http"
+
+	"sigs.k8s.io/controller-runtime/pkg/healthz"
+
+	"zotregistry.dev/zot/pkg/api/config"
+	"zotregistry.dev/zot/pkg/log"
+)
+
+var errNotReady = errors.New("not ready yet")
+
+type Healthz struct {
+	log     log.Logger
+	ready   bool
+	started bool
+	Handler *healthz.Handler
+}
+
+func NewHealthzServer(appConfig *config.Config, logger log.Logger) *Healthz {
+	var health Healthz
+	health.ready = false
+	health.started = false
+	health.log = logger
+	health.Handler = &healthz.Handler{Checks: map[string]healthz.Checker{
+		"livez":    health.livez,
+		"readyz":   health.readyz,
+		"startupz": health.startupz,
+	}}
+
+	return &health
+}
+
+func (h *Healthz) livez(req *http.Request) error {
+	return nil
+}
+
+func (h *Healthz) readyz(req *http.Request) error {
+	if h.ready {
+		return nil
+	}
+
+	return errNotReady
+}
+
+func (h *Healthz) startupz(req *http.Request) error {
+	if h.started {
+		return nil
+	}
+
+	return errNotReady
+}
+
+func (h *Healthz) Ready() {
+	h.ready = true
+	h.log.Debug().Msg("ready")
+}
+
+func (h *Healthz) Started() {
+	h.started = true
+	h.log.Debug().Msg("started")
+}