PBM-1565 automatic kerberos ticket renewal for pbm agent

cmd/pbm-agent/main.go

@@ -16,6 +16,7 @@ import (
 
 	"github.com/percona/percona-backup-mongodb/pbm/connect"
 	"github.com/percona/percona-backup-mongodb/pbm/errors"
+	"github.com/percona/percona-backup-mongodb/pbm/kinit"
 	"github.com/percona/percona-backup-mongodb/pbm/log"
 	"github.com/percona/percona-backup-mongodb/pbm/util"
 	"github.com/percona/percona-backup-mongodb/pbm/version"
@@ -123,6 +124,18 @@ func setRootFlags(rootCmd *cobra.Command) {
 	_ = viper.BindPFlag("log.level", rootCmd.Flags().Lookup("log-level"))
 	_ = viper.BindEnv("log.level", "LOG_LEVEL")
 	viper.SetDefault("log.level", log.D)
+
+	rootCmd.Flags().String("kerberos-keytab", "",
+		"Path to Kerberos keytab (if empty uses host keytab)")
+	_ = viper.BindPFlag("kerberos.keytab",
+		rootCmd.Flags().Lookup("kerberos-keytab"))
+	_ = viper.BindEnv("kerberos.keytab", "PBM_KERBEROS_KEYTAB")
+
+	rootCmd.Flags().Duration("kerberos-renew-interval", 0,
+		"How often to renew Kerberos ticket (if 0 renewal is disabled)")
+	_ = viper.BindPFlag("kerberos.renew-interval",
+		rootCmd.Flags().Lookup("kerberos-renew-interval"))
+	_ = viper.BindEnv("kerberos.renew-interval", "PBM_KERBEROS_RENEW_INTERVAL")
 }
 
 func versionCommand() *cobra.Command {
@@ -243,5 +256,24 @@ func runAgent(
 	}
 	go agent.HbStatus(ctx)
 
+	setupKerberosRenewal(ctx, mongoURI, logger)
+
 	return errors.Wrap(agent.Start(ctx), "listen the commands stream")
 }
+
+func setupKerberosRenewal(ctx context.Context, mongoURI string, l log.Logger) {
+	interval := viper.GetDuration("kerberos.renew-interval")
+	if interval <= 0 { // 0 or negative means disabled
+		return
+	}
+
+	keytab := viper.GetString("kerberos.keytab")
+
+	rm, err := kinit.New(mongoURI, keytab, interval)
+	if err != nil {
+		l.Printf("Kerberos renewal skipped: %s", err)
+		return
+	}
+
+	rm.Start(ctx)
+}

pbm/kinit/renewal.go

@@ -0,0 +1,99 @@
+package kinit
+
+import (
+	"context"
+	"net/url"
+	"os/exec"
+	"strings"
+	"time"
+
+	"go.mongodb.org/mongo-driver/bson/primitive"
+
+	"github.com/percona/percona-backup-mongodb/pbm/errors"
+	"github.com/percona/percona-backup-mongodb/pbm/log"
+)
+
+// Renewal periodically refreshes a Kerberos TGT using the `kinit` command-line tool.
+type Renewal struct {
+	Keytab    string
+	Principal string
+	Interval  time.Duration
+}
+
+func New(mongoURI, keytab string, interval time.Duration) (*Renewal, error) {
+	if _, err := exec.LookPath("kinit"); err != nil {
+		return nil, errors.New("kinit not found in PATH")
+	}
+
+	principal, err := principalFromMongoURI(mongoURI)
+	if err != nil {
+		return nil, errors.Wrap(err, "parsing principal")
+	}
+
+	return &Renewal{
+		Keytab:    keytab,
+		Principal: principal,
+		Interval:  interval,
+	}, nil
+}
+
+// Start performs an immediate renewal and then continues to renew the ticket every Interval.
+func (r Renewal) Start(ctx context.Context) {
+	l := log.FromContext(ctx).NewEvent("", "", "", primitive.Timestamp{})
+
+	if err := r.renew(ctx); err != nil {
+		l.Error("Kerberos ticket renewal failed: %v", err)
+	} else {
+		l.Info("Kerberos ticket obtained successfully")
+	}
+
+	tkr := time.NewTicker(r.Interval)
+	go func() {
+		defer tkr.Stop()
+		for {
+			select {
+			case <-ctx.Done():
+				return
+			case <-tkr.C:
+				if err := r.renew(ctx); err != nil {
+					l.Error("Kerberos ticket renewal failed: %v", err)
+				} else {
+					l.Info("Kerberos ticket obtained successfully")
+				}
+			}
+		}
+	}()
+}
+
+func (r Renewal) renew(ctx context.Context) error {
+	args := []string{"-k"}
+	if r.Keytab != "" {
+		args = append(args, "-t", r.Keytab)
+	}
+	args = append(args, r.Principal)
+
+	cmd := exec.CommandContext(ctx, "kinit", args...)
+	if out, err := cmd.CombinedOutput(); err != nil {
+		msg := strings.TrimSpace(string(out))
+		return errors.New(msg)
+	}
+	return nil
+}
+
+func principalFromMongoURI(uri string) (string, error) {
+	parsed, err := url.Parse(uri)
+	if err != nil {
+		return "", errors.Wrap(err, "cannot parse URI")
+	}
+
+	if parsed.User == nil {
+		return "", errors.New("no user info in URI")
+	}
+
+	principal := parsed.User.Username()
+	if principal == "" {
+		return "", errors.New("empty principal in URI")
+	}
+
+	return principal, nil
+}