[v18] Add teleport debug readyz command

tool/teleport/common/debug.go

@@ -44,6 +44,8 @@ type DebugClient interface {
 	GetLogLevel(context.Context) (string, error)
 	// CollectProfile collects a pprof profile.
 	CollectProfile(context.Context, string, int) ([]byte, error)
+	// GetReadiness checks if the instance is ready to serve requests.
+	GetReadiness(context.Context) (debugclient.Readiness, error)
 	SocketPath() string
 }
 
@@ -166,6 +168,34 @@ func collectProfiles(ctx context.Context, clt DebugClient, buf io.Writer, rawPro
 	return trace.NewAggregate(tw.Close(), gw.Close())
 }
 
+// onReadyz checks if the instance is ready to serve requests.
+func onReadyz(ctx context.Context, configPath string) error {
+	clt, dataDir, err := newDebugClient(configPath)
+	if err != nil {
+		return trace.Wrap(err)
+	}
+
+	if err := readyz(ctx, clt); err != nil {
+		return convertToReadableErr(err, dataDir, clt.SocketPath())
+	}
+
+	return nil
+}
+
+func readyz(ctx context.Context, clt DebugClient) error {
+	readiness, err := clt.GetReadiness(ctx)
+	if err != nil {
+		return trace.Wrap(err)
+	}
+
+	if !readiness.Ready {
+		return trace.Errorf("not ready (PID:%d): %s", readiness.PID, readiness.Status)
+	}
+
+	fmt.Printf("ready (PID:%d)\n", readiness.PID)
+	return nil
+}
+
 // newDebugClient initializes the debug client based on the Teleport
 // configuration. It also returns the data dir and socket path used.
 func newDebugClient(configPath string) (DebugClient, string, error) {

tool/teleport/common/teleport.go

@@ -617,6 +617,7 @@ func Run(options Options) (app *kingpin.Application, executedCommand string, con
 	collectProfilesCmd.Alias(collectProfileUsageExamples) // We're using "alias" section to display usage examples.
 	collectProfilesCmd.Arg("PROFILES", fmt.Sprintf("Comma-separated profile names to be exported. Supported profiles: %s. Default: %s", strings.Join(slices.Collect(maps.Keys(debugclient.SupportedProfiles)), ","), strings.Join(defaultCollectProfiles, ","))).StringVar(&ccf.Profiles)
 	collectProfilesCmd.Flag("seconds", "For CPU and trace profiles, profile for the given duration (if set to 0, it returns a profile snapshot). For other profiles, return a delta profile. Default: 0").Short('s').Default("0").IntVar(&ccf.ProfileSeconds)
+	readyzCmd := debugCmd.Command("readyz", "Checks if the instance is ready to serve requests.")
 
 	selinuxCmd := app.Command("selinux-ssh", "Commands related to SSH SELinux module.").Hidden()
 	selinuxCmd.Flag("config", fmt.Sprintf("Path to a configuration file [%v].", defaults.ConfigFilePath)).Short('c').ExistingFileVar(&ccf.ConfigFile)
@@ -810,6 +811,8 @@ Examples:
 		err = onGetLogLevel(ccf.ConfigFile)
 	case collectProfilesCmd.FullCommand():
 		err = onCollectProfiles(ccf.ConfigFile, ccf.Profiles, ccf.ProfileSeconds)
+	case readyzCmd.FullCommand():
+		err = onReadyz(ctx, ccf.ConfigFile)
 	case moduleSourceCmd.FullCommand():
 		if runtime.GOOS != "linux" {
 			break