Actually init logging using Zap (#267)

Controllers typically use Zap these days.
The only potential issue is that the flags are not compatible.
This is somehow mitigated by supporting -v explicitly.

go.mod

@@ -17,6 +17,7 @@ require (
 	github.com/prometheus/common v0.62.0
 	github.com/stretchr/testify v1.10.0
 	go.uber.org/multierr v1.11.0
+	go.uber.org/zap v1.27.0
 	google.golang.org/grpc v1.70.0
 	google.golang.org/protobuf v1.36.5
 	k8s.io/api v0.32.1
@@ -62,6 +63,7 @@ require (
 	github.com/fxamacker/cbor/v2 v2.7.0 // indirect
 	github.com/go-logr/logr v1.4.2 // indirect
 	github.com/go-logr/stdr v1.2.2 // indirect
+	github.com/go-logr/zapr v1.3.0 // indirect
 	github.com/go-openapi/jsonpointer v0.21.0 // indirect
 	github.com/go-openapi/jsonreference v0.20.2 // indirect
 	github.com/go-openapi/swag v0.23.0 // indirect
@@ -114,7 +116,6 @@ require (
 	go.opentelemetry.io/otel/sdk v1.32.0 // indirect
 	go.opentelemetry.io/otel/trace v1.32.0 // indirect
 	go.opentelemetry.io/proto/otlp v1.3.1 // indirect
-	go.uber.org/zap v1.27.0 // indirect
 	golang.org/x/crypto v0.32.0 // indirect
 	golang.org/x/exp v0.0.0-20240719175910-8a7402abbf56 // indirect
 	golang.org/x/mod v0.22.0 // indirect

pkg/ext-proc/main.go

@@ -9,6 +9,8 @@ import (
 	"strconv"
 
 	"github.com/prometheus/client_golang/prometheus/promhttp"
+	uberzap "go.uber.org/zap"
+	"go.uber.org/zap/zapcore"
 	"google.golang.org/grpc"
 	healthPb "google.golang.org/grpc/health/grpc_health_v1"
 	"k8s.io/apimachinery/pkg/runtime"
@@ -18,12 +20,14 @@ import (
 	"k8s.io/component-base/metrics/legacyregistry"
 	klog "k8s.io/klog/v2"
 	ctrl "sigs.k8s.io/controller-runtime"
+	"sigs.k8s.io/controller-runtime/pkg/log/zap"
 	"sigs.k8s.io/controller-runtime/pkg/metrics/filters"
 	"sigs.k8s.io/gateway-api-inference-extension/api/v1alpha1"
 	"sigs.k8s.io/gateway-api-inference-extension/pkg/ext-proc/backend"
 	"sigs.k8s.io/gateway-api-inference-extension/pkg/ext-proc/backend/vllm"
 	"sigs.k8s.io/gateway-api-inference-extension/pkg/ext-proc/metrics"
 	runserver "sigs.k8s.io/gateway-api-inference-extension/pkg/ext-proc/server"
+	"sigs.k8s.io/gateway-api-inference-extension/pkg/ext-proc/util/logging"
 )
 
 const (
@@ -73,6 +77,7 @@ var (
 		"refreshPrometheusMetricsInterval",
 		runserver.DefaultRefreshPrometheusMetricsInterval,
 		"interval to flush prometheus metrics")
+	logVerbosity = flag.Int("v", logging.DEFAULT, "number for the log level verbosity")
 
 	scheme = runtime.NewScheme()
 )
@@ -83,10 +88,13 @@ func init() {
 }
 
 func main() {
-	klog.InitFlags(nil)
+	opts := zap.Options{
+		Development: true,
+	}
+	opts.BindFlags(flag.CommandLine)
 	flag.Parse()
+	initLogging(&opts)
 
-	ctrl.SetLogger(klog.TODO())
 	cfg, err := ctrl.GetConfig()
 	if err != nil {
 		klog.Fatalf("Failed to get rest config: %v", err)
@@ -152,6 +160,25 @@ func main() {
 	klog.Info("All components shutdown")
 }
 
+func initLogging(opts *zap.Options) {
+	// Unless -zap-log-level is explicitly set, use -v
+	useV := true
+	flag.Visit(func(f *flag.Flag) {
+		if f.Name == "zap-log-level" {
+			useV = false
+		}
+	})
+	if useV {
+		// See https://pkg.go.dev/sigs.k8s.io/controller-runtime/pkg/log/zap#Options.Level
+		lvl := -1 * (*logVerbosity)
+		opts.Level = uberzap.NewAtomicLevelAt(zapcore.Level(int8(lvl)))
+	}
+
+	logger := zap.New(zap.UseFlagOptions(opts), zap.RawZapOpts(uberzap.AddCaller()))
+	ctrl.SetLogger(logger)
+	klog.SetLogger(logger)
+}
+
 // startHealthServer starts the gRPC health probe server in a goroutine.
 func startHealthServer(ds *backend.K8sDatastore, port int) *grpc.Server {
 	svr := grpc.NewServer()