adds config validation, similar to cortex (#1939)

cmd/loki/main.go

@@ -50,6 +50,14 @@ func main() {
 	}
 	util.InitLogger(&config.Server)
 
+	// Validate the config once both the config file has been loaded
+	// and CLI flags parsed.
+	err := config.Validate(util.Logger)
+	if err != nil {
+		level.Error(util.Logger).Log("msg", "validating config", "err", err.Error())
+		os.Exit(1)
+	}
+
 	// Setting the environment variable JAEGER_AGENT_HOST enables tracing
 	trace, err := tracing.NewFromEnv(fmt.Sprintf("loki-%s", config.Target))
 	if err != nil {

pkg/loki/loki.go

@@ -11,6 +11,7 @@ import (
 	"github.com/cortexproject/cortex/pkg/util"
 	"github.com/cortexproject/cortex/pkg/util/runtimeconfig"
 
+	"github.com/go-kit/kit/log"
 	"github.com/go-kit/kit/log/level"
 	"github.com/pkg/errors"
 	"github.com/weaveworks/common/middleware"
@@ -73,6 +74,24 @@ func (c *Config) RegisterFlags(f *flag.FlagSet) {
 	c.RuntimeConfig.RegisterFlags(f)
 }
 
+// Validate the config and returns an error if the validation
+// doesn't pass
+func (c *Config) Validate(log log.Logger) error {
+	if err := c.SchemaConfig.Validate(); err != nil {
+		return errors.Wrap(err, "invalid schema config")
+	}
+	if err := c.StorageConfig.Validate(); err != nil {
+		return errors.Wrap(err, "invalid storage config")
+	}
+	if err := c.QueryRange.Validate(log); err != nil {
+		return errors.Wrap(err, "invalid queryrange config")
+	}
+	if err := c.TableManager.Validate(); err != nil {
+		return errors.Wrap(err, "invalid tablemanager config")
+	}
+	return nil
+}
+
 // Loki is the root datastructure for Loki.
 type Loki struct {
 	cfg Config