receive": Make relabel config file optional (#141)

Allow thanos receive to start even if specified relabel config file path doesn't exist. The path is still polled and when the file gets created, its configuration will be loaded in.

Author: abhijith-db

pkg/receive/relabeller.go

@@ -6,6 +6,7 @@ package receive
 import (
 	"context"
 	"fmt"
+	"os"
 	"time"
 
 	"github.com/go-kit/log"
@@ -99,6 +100,12 @@ func (r *Relabeller) setRelabelConfig(configs RelabelConfig) {
 func (r *Relabeller) loadConfig() error {
 	relabelContentYaml, err := r.configPathOrContent.Content()
 	if err != nil {
+		// If file does not exist, we just set an empty config.
+		if errors.Is(err, os.ErrNotExist) {
+			level.Debug(r.logger).Log("msg", "relabel config file does not exist")
+			r.setRelabelConfig(RelabelConfig{})
+			return nil
+		}
 		return errors.Wrap(err, "getting content of relabel config")
 	}
 	var relabelConfig RelabelConfig