feat: allow logging output to use JSON formatter (#1705)

Co-authored-by: nils måsén <nils@piksel.se>

cmd/root.go

@@ -1,6 +1,7 @@
 package cmd
 
 import (
+	"errors"
 	"math"
 	"net/http"
 	"os"
@@ -78,23 +79,8 @@ func Execute() {
 func PreRun(cmd *cobra.Command, _ []string) {
 	f := cmd.PersistentFlags()
 	flags.ProcessFlagAliases(f)
-
-	if enabled, _ := f.GetBool("no-color"); enabled {
-		log.SetFormatter(&log.TextFormatter{
-			DisableColors: true,
-		})
-	} else {
-		// enable logrus built-in support for https://bixense.com/clicolors/
-		log.SetFormatter(&log.TextFormatter{
-			EnvironmentOverrideColors: true,
-		})
-	}
-
-	rawLogLevel, _ := f.GetString(`log-level`)
-	if logLevel, err := log.ParseLevel(rawLogLevel); err != nil {
-		log.Fatalf("Invalid log level: %s", err.Error())
-	} else {
-		log.SetLevel(logLevel)
+	if err := flags.SetupLogging(f); err != nil {
+		log.Fatalf("Failed to initialize logging: %s", err.Error())
 	}
 
 	scheduleSpec, _ = f.GetString("schedule")
@@ -201,7 +187,7 @@ func Run(c *cobra.Command, names []string) {
 		httpAPI.RegisterHandler(metricsHandler.Path, metricsHandler.Handle)
 	}
 
-	if err := httpAPI.Start(enableUpdateAPI && !unblockHTTPAPI); err != nil && err != http.ErrServerClosed {
+	if err := httpAPI.Start(enableUpdateAPI && !unblockHTTPAPI); err != nil && !errors.Is(err, http.ErrServerClosed) {
 		log.Error("failed to start API", err)
 	}
 

docs/arguments.md

@@ -134,6 +134,17 @@ Environment Variable: WATCHTOWER_LOG_LEVEL
              Default: info
 ```
 
+## Logging format
+
+Sets what logging format to use for console output.
+
+```text
+            Argument: --log-format, -l
+Environment Variable: WATCHTOWER_LOG_FORMAT
+     Possible values: Auto, LogFmt, Pretty or JSON
+             Default: Auto
+```
+
 ## ANSI colors
 Disable ANSI color escape codes in log output.
 
@@ -407,6 +418,7 @@ Environment Variable: WATCHTOWER_WARN_ON_HEAD_FAILURE
      Possible values: always, auto, never
              Default: auto
 ```
+
 ## Programatic Output (porcelain)
 
 Writes the session results to STDOUT using a stable, machine-readable format (indicated by the argument VERSION).  

internal/flags/flags.go

@@ -85,6 +85,12 @@ func RegisterSystemFlags(rootCmd *cobra.Command) {
 		envBool("WATCHTOWER_LABEL_ENABLE"),
 		"Watch containers where the com.centurylinklabs.watchtower.enable label is true")
 
+	flags.StringP(
+		"log-format",
+		"l",
+		viper.GetString("WATCHTOWER_LOG_FORMAT"),
+		"Sets what logging format to use for console output. Possible values: Auto, LogFmt, Pretty, JSON")
+
 	flags.BoolP(
 		"debug",
 		"d",
@@ -409,6 +415,7 @@ func SetDefaults() {
 	viper.SetDefault("WATCHTOWER_NOTIFICATION_EMAIL_SUBJECTTAG", "")
 	viper.SetDefault("WATCHTOWER_NOTIFICATION_SLACK_IDENTIFIER", "watchtower")
 	viper.SetDefault("WATCHTOWER_LOG_LEVEL", "info")
+	viper.SetDefault("WATCHTOWER_LOG_FORMAT", "auto")
 }
 
 // EnvConfig translates the command-line options into environment variables
@@ -611,6 +618,46 @@ func ProcessFlagAliases(flags *pflag.FlagSet) {
 
 }
 
+// SetupLogging reads only the flags that is needed to set up logging and applies them to the global logger
+func SetupLogging(f *pflag.FlagSet) error {
+	logFormat, _ := f.GetString(`log-format`)
+	noColor, _ := f.GetBool("no-color")
+
+	switch strings.ToLower(logFormat) {
+	case "auto":
+		// This will either use the "pretty" or "logfmt" format, based on whether the standard out is connected to a TTY
+		log.SetFormatter(&log.TextFormatter{
+			DisableColors: noColor,
+			// enable logrus built-in support for https://bixense.com/clicolors/
+			EnvironmentOverrideColors: true,
+		})
+	case "json":
+		log.SetFormatter(&log.JSONFormatter{})
+	case "logfmt":
+		log.SetFormatter(&log.TextFormatter{
+			DisableColors: true,
+			FullTimestamp: true,
+		})
+	case "pretty":
+		log.SetFormatter(&log.TextFormatter{
+			// "Pretty" format combined with `--no-color` will only change the timestamp to the time since start
+			ForceColors:   !noColor,
+			FullTimestamp: false,
+		})
+	default:
+		return fmt.Errorf("invalid log format: %s", logFormat)
+	}
+
+	rawLogLevel, _ := f.GetString(`log-level`)
+	if logLevel, err := log.ParseLevel(rawLogLevel); err != nil {
+		return fmt.Errorf("invalid log level: %e", err)
+	} else {
+		log.SetLevel(logLevel)
+	}
+
+	return nil
+}
+
 func flagIsEnabled(flags *pflag.FlagSet, name string) bool {
 	value, err := flags.GetBool(name)
 	if err != nil {

internal/flags/flags_test.go

@@ -177,6 +177,57 @@ func TestProcessFlagAliasesLogLevelFromEnvironment(t *testing.T) {
 	assert.Equal(t, `debug`, logLevel)
 }
 
+func TestLogFormatFlag(t *testing.T) {
+	cmd := new(cobra.Command)
+
+	SetDefaults()
+	RegisterDockerFlags(cmd)
+	RegisterSystemFlags(cmd)
+
+	// Ensure the default value is Auto
+	require.NoError(t, cmd.ParseFlags([]string{}))
+	require.NoError(t, SetupLogging(cmd.Flags()))
+	assert.IsType(t, &logrus.TextFormatter{}, logrus.StandardLogger().Formatter)
+
+	// Test JSON format
+	require.NoError(t, cmd.ParseFlags([]string{`--log-format`, `JSON`}))
+	require.NoError(t, SetupLogging(cmd.Flags()))
+	assert.IsType(t, &logrus.JSONFormatter{}, logrus.StandardLogger().Formatter)
+
+	// Test Pretty format
+	require.NoError(t, cmd.ParseFlags([]string{`--log-format`, `pretty`}))
+	require.NoError(t, SetupLogging(cmd.Flags()))
+	assert.IsType(t, &logrus.TextFormatter{}, logrus.StandardLogger().Formatter)
+	textFormatter, ok := (logrus.StandardLogger().Formatter).(*logrus.TextFormatter)
+	assert.True(t, ok)
+	assert.True(t, textFormatter.ForceColors)
+	assert.False(t, textFormatter.FullTimestamp)
+
+	// Test LogFmt format
+	require.NoError(t, cmd.ParseFlags([]string{`--log-format`, `logfmt`}))
+	require.NoError(t, SetupLogging(cmd.Flags()))
+	textFormatter, ok = (logrus.StandardLogger().Formatter).(*logrus.TextFormatter)
+	assert.True(t, ok)
+	assert.True(t, textFormatter.DisableColors)
+	assert.True(t, textFormatter.FullTimestamp)
+
+	// Test invalid format
+	require.NoError(t, cmd.ParseFlags([]string{`--log-format`, `cowsay`}))
+	require.Error(t, SetupLogging(cmd.Flags()))
+}
+
+func TestLogLevelFlag(t *testing.T) {
+	cmd := new(cobra.Command)
+
+	SetDefaults()
+	RegisterDockerFlags(cmd)
+	RegisterSystemFlags(cmd)
+
+	// Test invalid format
+	require.NoError(t, cmd.ParseFlags([]string{`--log-level`, `gossip`}))
+	require.Error(t, SetupLogging(cmd.Flags()))
+}
+
 func TestProcessFlagAliasesSchedAndInterval(t *testing.T) {
 	logrus.StandardLogger().ExitFunc = func(_ int) { panic(`FATAL`) }
 	cmd := new(cobra.Command)