refactor the pkg/util/cfg package to simplify and make it accessable …

…outside of this package.

create a pkg/cfg which handles building the Loki config, this is created separately from pkg/util (which is Apache 2 licensed) to maintain proper separations of AGPL and Apache 2 code
Update the main.go for several of the apps with the refactoring

clients/cmd/promtail/main.go

@@ -65,7 +65,7 @@ func (c *Config) Clone() flagext.Registerer {
 func main() {
 	// Load config, merging config file and CLI flags
 	var config Config
-	if err := cfg.Parse(&config); err != nil {
+	if err := cfg.DefaultUnmarshal(&config); err != nil {
 		fmt.Println("Unable to parse config:", err)
 		os.Exit(1)
 	}

cmd/loki/main.go

@@ -1,22 +1,20 @@
 package main
 
 import (
-	"flag"
 	"fmt"
 	"os"
 	"reflect"
 
 	"github.com/go-kit/kit/log/level"
-	"github.com/grafana/dskit/flagext"
 	"github.com/prometheus/client_golang/prometheus"
 	"github.com/prometheus/common/version"
 	"github.com/weaveworks/common/logging"
 	"github.com/weaveworks/common/tracing"
 
+	"github.com/grafana/loki/pkg/cfg"
 	"github.com/grafana/loki/pkg/loki"
 	logutil "github.com/grafana/loki/pkg/util"
 	_ "github.com/grafana/loki/pkg/util/build"
-	"github.com/grafana/loki/pkg/util/cfg"
 	"github.com/grafana/loki/pkg/validation"
 
 	util_log "github.com/cortexproject/cortex/pkg/util/log"
@@ -26,43 +24,14 @@ func init() {
 	prometheus.MustRegister(version.NewCollector("loki"))
 }
 
-type Config struct {
-	loki.Config     `yaml:",inline"`
-	printVersion    bool
-	verifyConfig    bool
-	printConfig     bool
-	logConfig       bool
-	configFile      string
-	configExpandEnv bool
-}
-
-func (c *Config) RegisterFlags(f *flag.FlagSet) {
-	f.BoolVar(&c.printVersion, "version", false, "Print this builds version information")
-	f.BoolVar(&c.verifyConfig, "verify-config", false, "Verify config file and exits")
-	f.BoolVar(&c.printConfig, "print-config-stderr", false, "Dump the entire Loki config object to stderr")
-	f.BoolVar(&c.logConfig, "log-config-reverse-order", false, "Dump the entire Loki config object at Info log "+
-		"level with the order reversed, reversing the order makes viewing the entries easier in Grafana.")
-	f.StringVar(&c.configFile, "config.file", "", "yaml file to load")
-	f.BoolVar(&c.configExpandEnv, "config.expand-env", false, "Expands ${var} in config according to the values of the environment variables.")
-	c.Config.RegisterFlags(f)
-}
-
-// Clone takes advantage of pass-by-value semantics to return a distinct *Config.
-// This is primarily used to parse a different flag set without mutating the original *Config.
-func (c *Config) Clone() flagext.Registerer {
-	return func(c Config) *Config {
-		return &c
-	}(*c)
-}
-
 func main() {
-	var config Config
+	var config cfg.ConfigWrapper
 
-	if err := cfg.Parse(&config); err != nil {
+	if err := cfg.Unmarshal(&config); err != nil {
 		fmt.Fprintf(os.Stderr, "failed parsing config: %v\n", err)
 		os.Exit(1)
 	}
-	if config.printVersion {
+	if config.PrintVersion {
 		fmt.Println(version.Print("loki"))
 		os.Exit(0)
 	}
@@ -87,19 +56,19 @@ func main() {
 		os.Exit(1)
 	}
 
-	if config.verifyConfig {
+	if config.VerifyConfig {
 		level.Info(util_log.Logger).Log("msg", "config is valid")
 		os.Exit(0)
 	}
 
-	if config.printConfig {
+	if config.PrintConfig {
 		err := logutil.PrintConfig(os.Stderr, &config)
 		if err != nil {
 			level.Error(util_log.Logger).Log("msg", "failed to print config to stderr", "err", err.Error())
 		}
 	}
 
-	if config.logConfig {
+	if config.LogConfig {
 		err := logutil.LogConfig(&config)
 		if err != nil {
 			level.Error(util_log.Logger).Log("msg", "failed to log config object", "err", err.Error())

cmd/migrate/main.go

@@ -52,7 +52,7 @@ func main() {
 	flag.Parse()
 
 	// Create a set of defaults
-	if err := cfg.Unmarshal(&defaultsConfig, cfg.Defaults()); err != nil {
+	if err := cfg.Unmarshal(&defaultsConfig, cfg.Defaults(flag.CommandLine)); err != nil {
 		log.Println("Failed parsing defaults config:", err)
 		os.Exit(1)
 	}

pkg/cfg/cfg.go

@@ -0,0 +1,85 @@
+package cfg
+
+import (
+	"flag"
+	"os"
+
+	"github.com/grafana/dskit/flagext"
+	"github.com/pkg/errors"
+
+	"github.com/grafana/loki/pkg/loki"
+	"github.com/grafana/loki/pkg/util/cfg"
+)
+
+// ConfigWrapper is a struct containing the Loki config along with other values that can be set on the command line
+// for interacting with the config file or the application directly.
+type ConfigWrapper struct {
+	loki.Config     `yaml:",inline"`
+	PrintVersion    bool
+	VerifyConfig    bool
+	PrintConfig     bool
+	LogConfig       bool
+	ConfigFile      string
+	ConfigExpandEnv bool
+}
+
+func (c *ConfigWrapper) RegisterFlags(f *flag.FlagSet) {
+	f.BoolVar(&c.PrintVersion, "version", false, "Print this builds version information")
+	f.BoolVar(&c.VerifyConfig, "verify-config", false, "Verify config file and exits")
+	f.BoolVar(&c.PrintConfig, "print-config-stderr", false, "Dump the entire Loki config object to stderr")
+	f.BoolVar(&c.LogConfig, "log-config-reverse-order", false, "Dump the entire Loki config object at Info log "+
+		"level with the order reversed, reversing the order makes viewing the entries easier in Grafana.")
+	f.StringVar(&c.ConfigFile, "config.file", "", "yaml file to load")
+	f.BoolVar(&c.ConfigExpandEnv, "config.expand-env", false, "Expands ${var} in config according to the values of the environment variables.")
+	c.Config.RegisterFlags(f)
+}
+
+// Clone takes advantage of pass-by-value semantics to return a distinct *Config.
+// This is primarily used to parse a different flag set without mutating the original *Config.
+func (c *ConfigWrapper) Clone() flagext.Registerer {
+	return func(c ConfigWrapper) *ConfigWrapper {
+		return &c
+	}(*c)
+}
+
+// Unmarshal handles populating Loki's config based on the following precedence:
+// 1. Defaults provided by the `RegisterFlags` interface
+// 2. Sections populated by the `common` config section of the Loki config
+// 3. Any config options specified directly in the loki config file
+// 4. Any config options specified on the command line.
+func Unmarshal(dst cfg.Cloneable) error {
+	return cfg.Unmarshal(dst,
+		// First populate the config with defaults including flags from the command line
+		cfg.Defaults(flag.CommandLine),
+		// Next populate the config from the config file, we do this to populate the `common`
+		// section of the config file by taking advantage of the code in YAMLFlag which will load
+		// and process the config file.
+		cfg.YAMLFlag(os.Args[1:], "config.file"),
+		// Apply our logic to use values from the common section to set values throughout the Loki config.
+		CommonConfig(),
+		// Load configs from the config file a second time, this will supersede anything set by the common
+		// config with values specified in the config file.
+		cfg.YAMLFlag(os.Args[1:], "config.file"),
+		// Load the flags again, this will supersede anything set from config file with flags from the command line.
+		cfg.Flags(),
+	)
+}
+
+// CommonConfig applies all rules for setting Loki config values from the common section of the Loki config file.
+// This entire method's purpose is to simplify Loki's config in an opinionated way so that Loki can be run
+// with the minimal amount of config options for most use cases. It also aims to reduce redundancy where
+// some values are set multiple times through the Loki config.
+func CommonConfig() cfg.Source {
+	return func(dst cfg.Cloneable) error {
+		r, ok := dst.(*ConfigWrapper)
+		if !ok {
+			return errors.New("dst is not a Loki ConfigWrapper")
+		}
+
+		// Apply all our custom logic here to set values in the Loki config from values in the common config
+		// FIXME this is just an example showing how we can use values from the common section to set values on the Loki config object
+		r.StorageConfig.BoltDBShipperConfig.SharedStoreType = r.Common.Store
+
+		return nil
+	}
+}

pkg/cfg/common/common.go

@@ -0,0 +1,5 @@
+package common
+
+type Config struct {
+	Store string // This is just an example, but here we should define all the 'common' config values used to set other Loki values.
+}

pkg/loki/loki.go

@@ -31,6 +31,7 @@ import (
 	"github.com/weaveworks/common/signals"
 	"google.golang.org/grpc/health/grpc_health_v1"
 
+	"github.com/grafana/loki/pkg/cfg/common"
 	"github.com/grafana/loki/pkg/distributor"
 	"github.com/grafana/loki/pkg/ingester"
 	"github.com/grafana/loki/pkg/ingester/client"
@@ -52,6 +53,7 @@ type Config struct {
 	AuthEnabled bool                   `yaml:"auth_enabled,omitempty"`
 	HTTPPrefix  string                 `yaml:"http_prefix"`
 
+	Common           common.Config            `yaml:"common,omitempty"`
 	Server           server.Config            `yaml:"server,omitempty"`
 	Distributor      distributor.Config       `yaml:"distributor,omitempty"`
 	Querier          querier.Config           `yaml:"querier,omitempty"`

pkg/util/cfg/cfg.go

@@ -44,27 +44,11 @@ func Unmarshal(dst Cloneable, sources ...Source) error {
 	return nil
 }
 
-// Parse is a higher level wrapper for Unmarshal that automatically parses flags and a .yaml file
-func Parse(dst Cloneable) error {
-	return dParse(dst,
-		dDefaults(flag.CommandLine),
+// DefaultUnmarshal is a higher level wrapper for Unmarshal that automatically parses flags and a .yaml file
+func DefaultUnmarshal(dst Cloneable) error {
+	return Unmarshal(dst,
+		Defaults(flag.CommandLine),
 		YAMLFlag(os.Args[1:], "config.file"),
 		Flags(),
 	)
 }
-
-// dParse is the same as Parse, but with dependency injection for testing
-func dParse(dst Cloneable, defaults, yaml, flags Source) error {
-	// check dst is a pointer
-	v := reflect.ValueOf(dst)
-	if v.Kind() != reflect.Ptr {
-		return ErrNotPointer
-	}
-
-	// unmarshal config
-	return Unmarshal(dst,
-		defaults,
-		yaml,
-		flags,
-	)
-}

pkg/util/cfg/cfg_test.go

@@ -22,8 +22,8 @@ tls:
 	flagSource := dFlags(fs, []string{"-verbose", "-server.port=21"})
 
 	data := Data{}
-	err := dParse(&data,
-		dDefaults(fs),
+	err := Unmarshal(&data,
+		Defaults(fs),
 		yamlSource,
 		flagSource,
 	)
@@ -55,8 +55,8 @@ tls:
 	flagSource := dFlags(fs, []string{"-verbose", "-server.port=21"})
 
 	data := Data{}
-	err := dParse(&data,
-		dDefaults(fs),
+	err := Unmarshal(&data,
+		Defaults(fs),
 		yamlSource,
 		flagSource,
 	)

pkg/util/cfg/flag.go

@@ -11,14 +11,8 @@ import (
 	"github.com/pkg/errors"
 )
 
-// Defaults registers flags to the command line using dst as the
-// flagext.Registerer
-func Defaults() Source {
-	return dDefaults(flag.CommandLine)
-}
-
-// dDefaults registers flags to the flagSet using dst as the flagext.Registerer
-func dDefaults(fs *flag.FlagSet) Source {
+// Defaults registers flags to the flagSet using dst as the flagext.Registerer
+func Defaults(fs *flag.FlagSet) Source {
 	return func(dst Cloneable) error {
 		r, ok := dst.(flagext.Registerer)
 		if !ok {

pkg/util/cfg/flag_test.go

@@ -16,7 +16,7 @@ func TestDefaults(t *testing.T) {
 	fs := flag.NewFlagSet(t.Name(), flag.PanicOnError)
 
 	err := Unmarshal(&data,
-		dDefaults(fs),
+		Defaults(fs),
 	)
 
 	require.NoError(t, err)
@@ -39,7 +39,7 @@ func TestFlags(t *testing.T) {
 	data := Data{}
 	fs := flag.NewFlagSet(t.Name(), flag.PanicOnError)
 	err := Unmarshal(&data,
-		dDefaults(fs),
+		Defaults(fs),
 		dFlags(fs, []string{"-server.timeout=10h", "-verbose"}),
 	)
 	require.NoError(t, err)

pkg/util/cfg/precedence_test.go

@@ -27,7 +27,7 @@ func TestYAMLOverDefaults(t *testing.T) {
 	data := Data{}
 	fs := flag.NewFlagSet(t.Name(), flag.PanicOnError)
 	err := Unmarshal(&data,
-		dDefaults(fs),
+		Defaults(fs),
 		dYAML([]byte(y)),
 	)
 
@@ -50,7 +50,7 @@ func TestFlagOverYAML(t *testing.T) {
 	fs := flag.NewFlagSet(t.Name(), flag.PanicOnError)
 
 	err := Unmarshal(&data,
-		dDefaults(fs),
+		Defaults(fs),
 		dYAML([]byte(y)),
 		dFlags(fs, []string{"-verbose=false", "-tls.cert=CLI"}),
 	)