PMM-14431 Skip non primary.

Author: JiriCtvrtka

exporter/metrics.go

@@ -24,6 +24,7 @@ import (
 	"sync"
 	"time"
 
+	"github.com/percona/mongodb_exporter/internal/util"
 	"github.com/pkg/errors"
 	"github.com/prometheus/client_golang/prometheus"
 	"go.mongodb.org/mongo-driver/bson"
@@ -213,6 +214,9 @@ func allReservedNames(client *mongo.Client) ([]string, error) {
 	reservedNames := []string{}
 	dbs, err := client.ListDatabaseNames(ctx, struct{}{})
 	if err != nil {
+		if cmdErr, ok := err.(mongo.CommandError); ok && cmdErr.Code == util.ErrNotPrimaryOrSecondary {
+			return []string{}, nil
+		}
 		return reservedNames, errors.Wrap(err, "ListDatabaseNames failed")
 	}