[#44] node: Support multiple configs

Signed-off-by: Denis Kirillov <d.kirillov@yadro.com>

cmd/frostfs-node/config/config.go

@@ -5,6 +5,7 @@ import (
 	"strings"
 
 	"github.com/TrueCloudLab/frostfs-node/cmd/frostfs-node/config/internal"
+	"github.com/TrueCloudLab/frostfs-node/pkg/util/config"
 	"github.com/spf13/viper"
 )
 
@@ -54,6 +55,12 @@ func New(_ Prm, opts ...Option) *Config {
 		}
 	}
 
+	if o.configDir != "" {
+		if err := config.ReadConfigDir(v, o.configDir); err != nil {
+			panic(fmt.Errorf("failed to read config dir: %w", err))
+		}
+	}
+
 	return &Config{
 		v:    v,
 		opts: *o,
@@ -69,5 +76,11 @@ func (x *Config) Reload() error {
 		}
 	}
 
+	if x.opts.configDir != "" {
+		if err := config.ReadConfigDir(x.v, x.opts.configDir); err != nil {
+			return fmt.Errorf("rereading configuration dir: %w", err)
+		}
+	}
+
 	return nil
 }

cmd/frostfs-node/config/opts.go

@@ -1,7 +1,8 @@
 package config
 
 type opts struct {
-	path string
+	path      string
+	configDir string
 }
 
 func defaultOpts() *opts {
@@ -18,3 +19,11 @@ func WithConfigFile(path string) Option {
 		o.path = path
 	}
 }
+
+// WithConfigDir returns an option to set the system path
+// to the directory with configuration files.
+func WithConfigDir(path string) Option {
+	return func(o *opts) {
+		o.configDir = path
+	}
+}

cmd/frostfs-node/main.go

@@ -34,6 +34,7 @@ func fatalOnErrDetails(details string, err error) {
 
 func main() {
 	configFile := flag.String("config", "", "path to config")
+	configDir := flag.String("config-dir", "", "path to config directory")
 	versionFlag := flag.Bool("version", false, "frostfs node version")
 	dryRunFlag := flag.Bool("check", false, "validate configuration and exit")
 	flag.Parse()
@@ -44,7 +45,7 @@ func main() {
 		os.Exit(SuccessReturnCode)
 	}
 
-	appCfg := config.New(config.Prm{}, config.WithConfigFile(*configFile))
+	appCfg := config.New(config.Prm{}, config.WithConfigFile(*configFile), config.WithConfigDir(*configDir))
 
 	err := validateConfig(appCfg)
 	fatalOnErr(err)

config/example/README.md

@@ -16,6 +16,67 @@ It is not recommended transferring these configs for real application launches.
 - CLI
   - YAML: `cli.yaml`
   
+### Multiple configs
+
+You can split your configuration to several files.
+For example, you can use separate yaml file for each shard or each service (pprof, prometheus).
+You must use `--config-dir` flag to process several configs:
+
+```shell
+$ ./bin/frotsfs-node --config ./config/example/node.yaml --config-dir ./dir/with/additional/configs
+```
+
+When the `--config-dir` flag set, the application:
+* reads all `*.y[a]ml` files from provided directory,
+* use Viper's [MergeConfig](https://pkg.go.dev/github.com/spf13/viper#MergeConfig) functionality to produce the final configuration,
+* files are being processing in alphanumerical order so that `01.yaml` may be extended with contents of `02.yaml`.
+
+So if we have the following files:
+```yaml
+# 00.yaml
+logger:
+  level: debug
+pprof:
+  enabled: true
+  address: localhost:6060
+prometheus:
+  enabled: true
+  address: localhost:9090
+```
+
+```yaml
+# dir/01.yaml
+logger:
+  level: info
+pprof:
+  enabled: false
+```
+
+```yaml
+# dir/02.yaml
+logger:
+  level: warn
+prometheus:
+  address: localhost:9091
+```
+
+and provide the following flags:
+```shell
+$ ./bin/frotsfs-node --config 00.yaml --config-dir dir
+```
+
+result config will be:
+```yaml
+logger:
+  level: warn
+pprof:
+  enabled: false
+  address: localhost:6060
+prometheus:
+  enabled: true
+  address: localhost:9091
+```
+
 ## Environment variables
 
 - Storage node: `node.env`

pkg/util/config/dir.go

@@ -0,0 +1,55 @@
+package config
+
+import (
+	"os"
+	"path"
+
+	"github.com/spf13/viper"
+)
+
+// ReadConfigDir reads all config files from provided directory in alphabetical order
+// and merge its content with current viper configuration.
+func ReadConfigDir(v *viper.Viper, configDir string) error {
+	entries, err := os.ReadDir(configDir)
+	if err != nil {
+		return err
+	}
+
+	for _, entry := range entries {
+		if entry.IsDir() {
+			continue
+		}
+		ext := path.Ext(entry.Name())
+		if ext != ".yaml" && ext != ".yml" {
+			continue
+		}
+
+		if err = mergeConfig(v, path.Join(configDir, entry.Name())); err != nil {
+			return err
+		}
+	}
+
+	return nil
+}
+
+// mergeConfig reads config file and merge its content with current viper.
+func mergeConfig(v *viper.Viper, fileName string) (err error) {
+	var cfgFile *os.File
+	cfgFile, err = os.Open(fileName)
+	if err != nil {
+		return err
+	}
+
+	defer func() {
+		errClose := cfgFile.Close()
+		if err == nil {
+			err = errClose
+		}
+	}()
+
+	if err = v.MergeConfig(cfgFile); err != nil {
+		return err
+	}
+
+	return nil
+}