Enable feature-gates for otel subcommands (#4198)

Added support for feature gates for otel and validate commands
How to test

- Build/Package agent
- run ./elastic-agent otel --feature-gates "-telemetry.useOtelForInternalMetrics" as this is stable feature gate, you should see error returned saying useOtelForInternalMetrics is stable and cannot be disabled
- running ./elastic-agent otel --feature-gates telemetry.useOtelForInternalMetrics (difference is - in front of a gate name) should result in a warning message in output saying it's stable and collector running normally
- running ./elastic-agent otel -h needs to include flag in help message

go.mod

@@ -65,6 +65,7 @@ require (
 	go.opentelemetry.io/collector/exporter v0.93.0
 	go.opentelemetry.io/collector/exporter/debugexporter v0.93.0
 	go.opentelemetry.io/collector/exporter/otlpexporter v0.93.0
+	go.opentelemetry.io/collector/featuregate v1.0.1
 	go.opentelemetry.io/collector/otelcol v0.93.0
 	go.opentelemetry.io/collector/processor v0.93.0
 	go.opentelemetry.io/collector/processor/batchprocessor v0.93.0
@@ -214,7 +215,6 @@ require (
 	go.opentelemetry.io/collector/consumer v0.93.0 // indirect
 	go.opentelemetry.io/collector/extension v0.93.0 // indirect
 	go.opentelemetry.io/collector/extension/auth v0.93.0 // indirect
-	go.opentelemetry.io/collector/featuregate v1.0.1 // indirect
 	go.opentelemetry.io/collector/pdata v1.0.1 // indirect
 	go.opentelemetry.io/collector/semconv v0.93.0 // indirect
 	go.opentelemetry.io/collector/service v0.93.0 // indirect

internal/pkg/agent/cmd/common.go

@@ -42,9 +42,11 @@ func NewCommandWithArgs(args []string, streams *cli.IOStreams) *cobra.Command {
 	}
 
 	// Init version information contained in package version file
-	err := version.InitVersionError()
-	if err != nil {
-		cmd.PrintErrf("Error initializing version information: %v\n", err)
+	if isOtel := len(args) > 1 && args[1] == "otel"; !isOtel {
+		err := version.InitVersionError()
+		if err != nil {
+			cmd.PrintErrf("Error initializing version information: %v\n", err)
+		}
 	}
 
 	// path flags

internal/pkg/agent/cmd/otel.go

@@ -48,12 +48,7 @@ func newOtelCommandWithArgs(args []string, streams *cli.IOStreams) *cobra.Comman
 		c.Root().HelpFunc()(c, s)
 	})
 
-	cmd.Flags().StringArray(configFlagName, []string{}, "Locations to the config file(s), note that only a"+
-		" single location can be set per flag entry e.g. `--config=file:/path/to/first --config=file:path/to/second`.")
-
-	cmd.Flags().StringArray(setFlagName, []string{}, "Set arbitrary component config property. The component has to be defined in the config file and the flag"+
-		" has a higher precedence. Array config properties are overridden and maps are joined. Example --set=processors.batch.timeout=2s")
-
+	setupOtelFlags(cmd.Flags())
 	cmd.AddCommand(newValidateCommandWithArgs(args, streams))
 
 	return cmd

internal/pkg/agent/cmd/otel_flags.go

@@ -5,14 +5,30 @@
 package cmd
 
 import (
+	"flag"
 	"fmt"
 	"strings"
 
 	"github.com/spf13/cobra"
+	"github.com/spf13/pflag"
+	"go.opentelemetry.io/collector/featuregate"
 
 	"github.com/elastic/elastic-agent/internal/pkg/agent/application/paths"
 )
 
+func setupOtelFlags(flags *pflag.FlagSet) {
+	flags.StringArray(configFlagName, []string{}, "Locations to the config file(s), note that only a"+
+		" single location can be set per flag entry e.g. `--config=file:/path/to/first --config=file:path/to/second`.")
+
+	flags.StringArray(setFlagName, []string{}, "Set arbitrary component config property. The component has to be defined in the config file and the flag"+
+		" has a higher precedence. Array config properties are overridden and maps are joined. Example --set=processors.batch.timeout=2s")
+
+	goFlags := new(flag.FlagSet)
+	featuregate.GlobalRegistry().RegisterFlags(goFlags)
+
+	flags.AddGoFlagSet(goFlags)
+}
+
 func getConfigFiles(cmd *cobra.Command, useDefault bool) ([]string, error) {
 	configFiles, err := cmd.Flags().GetStringArray(configFlagName)
 	if err != nil {

internal/pkg/agent/cmd/otel_flags_test.go

@@ -7,10 +7,26 @@ package cmd
 import (
 	"testing"
 
+	"github.com/spf13/pflag"
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
 )
 
+func TestOtelFlagsSetup(t *testing.T) {
+	fs := new(pflag.FlagSet)
+	setupOtelFlags(fs)
+
+	expectedFlags := []string{
+		configFlagName,
+		setFlagName,
+		"feature-gates",
+	}
+
+	for _, expectedFlag := range expectedFlags {
+		require.NotNil(t, fs.Lookup(expectedFlag), "Flag %q is not present", expectedFlag)
+	}
+}
+
 func TestGetSets(t *testing.T) {
 	testCases := []struct {
 		name          string

internal/pkg/agent/cmd/validate.go

@@ -28,12 +28,7 @@ func newValidateCommandWithArgs(_ []string, _ *cli.IOStreams) *cobra.Command {
 		},
 	}
 
-	cmd.Flags().StringArray(configFlagName, []string{}, "Locations to the config file(s), note that only a"+
-		" single location can be set per flag entry e.g. `--config=file:/path/to/first --config=file:path/to/second`.")
-
-	cmd.Flags().StringArray(setFlagName, []string{}, "Set arbitrary component config property. The component has to be defined in the config file and the flag"+
-		" has a higher precedence. Array config properties are overridden and maps are joined. Example --set=processors.batch.timeout=2s")
-
+	setupOtelFlags(cmd.Flags())
 	cmd.SetHelpFunc(func(c *cobra.Command, s []string) {
 		hideInheritedFlags(c)
 		c.Root().HelpFunc()(c, s)

testing/integration/otel_test.go

@@ -203,6 +203,11 @@ func validateCommandIsWorking(t *testing.T, ctx context.Context, fixture *aTesti
 	require.NoError(t, err)
 	require.Equal(t, 0, len(out)) // no error printed out
 
+	// check feature gate works
+	out, err = fixture.Exec(ctx, []string{"otel", "validate", "--config", cfgFilePath, "--feature-gates", "foo.bar"})
+	require.Error(t, err)
+	require.Contains(t, string(out), `no such feature gate "foo.bar"`)
+
 	// check `elastic-agent otel validate` command works for invalid otel config
 	cfgFilePath = filepath.Join(tempDir, "otel-invalid.yml")
 	require.NoError(t, os.WriteFile(cfgFilePath, []byte(fileInvalidOtelConfig), 0600))