Add support for JSON-formatted logging

cmd/cloud-controller-manager/app/controllermanager.go

@@ -83,6 +83,8 @@ func NewCloudControllerManagerCommand() *cobra.Command {
 		Use:  "cloud-controller-manager",
 		Long: `The Cloud controller manager is a daemon that embeds the cloud specific control loops shipped with Kubernetes.`,
 		Run: func(cmd *cobra.Command, _ []string) {
+			log.Setup(log.OptionsFromCLIFlags(cmd.Flags()))
+			defer log.Flush()
 			verflag.PrintAndExitIfRequested("Cloud Provider Azure")
 			cliflag.PrintFlags(cmd.Flags())
 
@@ -203,6 +205,8 @@ func NewCloudControllerManagerCommand() *cobra.Command {
 		cliflag.PrintSections(cmd.OutOrStdout(), namedFlagSets, cols)
 	})
 
+	log.BindCLIFlags(fs)
+
 	return cmd
 }
 

cmd/cloud-controller-manager/controller-manager.go

@@ -24,25 +24,19 @@ import (
 	"os"
 	"time"
 
-	"k8s.io/component-base/logs"
 	_ "k8s.io/component-base/metrics/prometheus/clientgo" // load all the prometheus client-go plugins
 
 	"sigs.k8s.io/cloud-provider-azure/cmd/cloud-controller-manager/app"
+	"sigs.k8s.io/cloud-provider-azure/pkg/log"
 	_ "sigs.k8s.io/cloud-provider-azure/pkg/provider"
 )
 
 func main() {
-	rand.Seed(time.Now().UnixNano())
+	rand.Seed(time.Now().UnixNano()) // FIXME: should use crypto/rand for better randomness
+	defer log.Flush()
 
 	command := app.NewCloudControllerManagerCommand()
 
-	// TODO: once we switch everything over to Cobra commands, we can go back to calling
-	// utilflag.InitFlags() (by removing its pflag.Parse() call). For now, we have to set the
-	// normalize func and add the go flag set by hand.
-	// utilflag.InitFlags()
-	logs.InitLogs()
-	defer logs.FlushLogs()
-
 	if err := command.Execute(); err != nil {
 		os.Exit(1)
 	}

pkg/log/flag.go

@@ -0,0 +1,67 @@
+/*
+Copyright 2024 The Kubernetes Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package log
+
+import (
+	"time"
+
+	"github.com/spf13/pflag"
+)
+
+type Format string
+
+const (
+	JSON Format = "json"
+	Text Format = "text"
+)
+
+const (
+	flagLogFormat         = "log-format"
+	flagLogFlushFrequency = "log-flush-frequency"
+
+	DefaultFormat         = Text
+	DefaultFlushFrequency = 5 * time.Second
+)
+
+func BindCLIFlags(fs *pflag.FlagSet) {
+	fs.String(flagLogFormat, "text", "The log format to use. One of: text, json.")
+	// log-flush-frequency is registered in kubernetes component-base.
+}
+
+type Options struct {
+	Format         Format
+	FlushFrequency time.Duration
+}
+
+func OptionsFromCLIFlags(fs *pflag.FlagSet) *Options {
+	var o Options
+
+	o.Format = Format(fs.Lookup(flagLogFormat).Value.String())
+	if o.Format != JSON && o.Format != Text {
+		SetupError("Invalid log format", flagLogFormat, o.Format)
+		o.Format = DefaultFormat
+	}
+
+	freq, err := fs.GetDuration(flagLogFlushFrequency)
+	if err != nil {
+		SetupError("Invalid log flush frequency", flagLogFlushFrequency, err)
+		o.FlushFrequency = DefaultFlushFrequency
+	}
+	o.FlushFrequency = freq
+
+	return &o
+}

pkg/log/logger.go

@@ -20,8 +20,12 @@ import (
 	"context"
 	"encoding/json"
 	"fmt"
+	"log"
+	"log/slog"
+	"os"
 
 	"github.com/go-logr/logr"
+	"k8s.io/component-base/logs"
 	"k8s.io/klog/v2"
 )
 
@@ -65,3 +69,36 @@ func ValueAsMap(value any) map[string]any {
 
 	return rv
 }
+
+// Setup initializes the logging system.
+func Setup(opts *Options) {
+	log.SetOutput(logs.KlogWriter{})
+	log.SetFlags(0)
+	klog.StartFlushDaemon(opts.FlushFrequency)
+
+	if opts.Format != JSON {
+		return
+	}
+
+	logger := slog.New(NewJSONHandler(os.Stdout, &slog.HandlerOptions{
+		Level:     slog.Level(-127), // Set to minimum level; actual filtering is handled by klog.V(N)
+		AddSource: true,
+		ReplaceAttr: func(_ []string, attr slog.Attr) slog.Attr {
+			switch attr.Key {
+			case slog.TimeKey:
+				// Avoid non-deterministic time field
+				return slog.Attr{}
+			default:
+				return attr
+			}
+		},
+	}))
+
+	slog.SetDefault(logger)
+	klog.SetSlogLogger(logger)
+}
+
+// Flush flushes logs immediately.
+func Flush() {
+	klog.Flush()
+}

pkg/log/slog.go

@@ -0,0 +1,65 @@
+/*
+Copyright 2024 The Kubernetes Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package log
+
+import (
+	"context"
+	"io"
+	"log/slog"
+)
+
+const (
+	TimeKey      = slog.TimeKey
+	LevelKey     = slog.LevelKey
+	VerbosityKey = "v"
+)
+
+type SLogJSONHandler struct {
+	handler *slog.JSONHandler
+}
+
+func NewJSONHandler(w io.Writer, opts *slog.HandlerOptions) *SLogJSONHandler {
+	return &SLogJSONHandler{
+		handler: slog.NewJSONHandler(w, opts),
+	}
+}
+
+func (h *SLogJSONHandler) Enabled(ctx context.Context, level slog.Level) bool {
+	return h.handler.Enabled(ctx, level)
+}
+
+func (h *SLogJSONHandler) Handle(ctx context.Context, record slog.Record) error {
+	// Extract verbosity from negative log levels and set it as an attribute.
+	// This is necessary because slog will convert negative levels to DEBUG+N.
+	if record.Level < 0 {
+		verbosity := int(-record.Level)
+		record.Level = slog.LevelInfo
+		record.AddAttrs(slog.Int(VerbosityKey, verbosity))
+	} else {
+		record.AddAttrs(slog.Int(VerbosityKey, 0))
+	}
+
+	return h.handler.Handle(ctx, record)
+}
+
+func (h *SLogJSONHandler) WithAttrs(attrs []slog.Attr) slog.Handler {
+	return h.handler.WithAttrs(attrs)
+}
+
+func (h *SLogJSONHandler) WithGroup(name string) slog.Handler {
+	return h.handler.WithGroup(name)
+}

pkg/log/std.go

@@ -0,0 +1,25 @@
+/*
+Copyright 2024 The Kubernetes Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package log
+
+import (
+	"log/slog"
+)
+
+func SetupError(msg string, args ...any) {
+	slog.Error(msg, args...)
+}