Implement an API for performance monitoring

Signed-off-by: Alexei Dodon <adodon@cisco.com>

pkg/exporter/cli/cli.go

@@ -0,0 +1,76 @@
+// +build minimal
+
+package cli
+
+import (
+	"github.com/anuvu/zot/errors"
+	"github.com/anuvu/zot/pkg/exporter/api"
+
+	"github.com/mitchellh/mapstructure"
+	"github.com/rs/zerolog/log"
+	"github.com/spf13/cobra"
+	"github.com/spf13/viper"
+)
+
+// metadataConfig reports metadata after parsing, which we use to track
+// errors.
+func metadataConfig(md *mapstructure.Metadata) viper.DecoderConfigOption {
+	return func(c *mapstructure.DecoderConfig) {
+		c.Metadata = md
+	}
+}
+
+func NewExporterCmd() *cobra.Command {
+	config := api.DefaultConfig()
+
+	// "config"
+	configCmd := &cobra.Command{
+		Use:     "config <config_file>",
+		Aliases: []string{"config"},
+		Short:   "`config` node exporter properties",
+		Long:    "`config` node exporter properties",
+		Run: func(cmd *cobra.Command, args []string) {
+			if len(args) > 0 {
+				loadConfiguration(config, args[0])
+			}
+
+			c := api.NewController(config)
+			c.Run()
+		},
+	}
+
+	// "node_exporter"
+	exporterCmd := &cobra.Command{
+		Use:   "zot_exporter",
+		Short: "`zot_exporter`",
+		Long:  "`zot_exporter`",
+		Run: func(cmd *cobra.Command, args []string) {
+			_ = cmd.Usage()
+			cmd.SilenceErrors = false
+		},
+	}
+
+	exporterCmd.AddCommand(configCmd)
+
+	return exporterCmd
+}
+
+func loadConfiguration(config *api.Config, configPath string) {
+	viper.SetConfigFile(configPath)
+
+	if err := viper.ReadInConfig(); err != nil {
+		log.Error().Err(err).Msg("Error while reading configuration")
+		panic(err)
+	}
+
+	md := &mapstructure.Metadata{}
+	if err := viper.Unmarshal(&config, metadataConfig(md)); err != nil {
+		log.Error().Err(err).Msg("Error while unmarshalling new config")
+		panic(err)
+	}
+
+	if len(md.Keys) == 0 || len(md.Unused) > 0 {
+		log.Error().Err(errors.ErrBadConfig).Msg("Bad configuration, retry writing it")
+		panic(errors.ErrBadConfig)
+	}
+}