Initial revisin of healthchecker, inspired by HAProxy

cmd/healthchecker/main.go

@@ -0,0 +1,111 @@
+package main
+
+import (
+	"context"
+	"flag"
+	"fmt"
+	"log/slog"
+	"net"
+	"os"
+	"os/signal"
+	"syscall"
+
+	"google.golang.org/grpc"
+
+	"git.ipng.ch/ipng/vpp-maglev/internal/checker"
+	"git.ipng.ch/ipng/vpp-maglev/internal/config"
+	"git.ipng.ch/ipng/vpp-maglev/internal/grpcapi"
+)
+
+func main() {
+	if err := run(); err != nil {
+		slog.Error("startup-fatal", "err", err)
+		os.Exit(1)
+	}
+}
+
+func run() error {
+	// ---- flags / env --------------------------------------------------------
+	configPath := stringFlag("config", "/etc/maglev/frontend.yaml", "MAGLEV_CONFIG", "path to frontend.yaml")
+	grpcAddr := stringFlag("grpc-addr", ":9090", "MAGLEV_GRPC_ADDR", "gRPC listen address")
+	logLevel := stringFlag("log-level", "info", "MAGLEV_LOG_LEVEL", "log level (debug|info|warn|error)")
+	flag.Parse()
+
+	// ---- logging ------------------------------------------------------------
+	var level slog.Level
+	if err := level.UnmarshalText([]byte(*logLevel)); err != nil {
+		return fmt.Errorf("invalid log level %q: %w", *logLevel, err)
+	}
+	slog.SetDefault(slog.New(slog.NewJSONHandler(os.Stdout, &slog.HandlerOptions{Level: level})))
+
+	// ---- config -------------------------------------------------------------
+	cfg, err := config.Load(*configPath)
+	if err != nil {
+		return fmt.Errorf("load config: %w", err)
+	}
+	slog.Info("config-loaded", "path", *configPath, "vips", len(cfg.VIPs))
+
+	// ---- checker ------------------------------------------------------------
+	chkr := checker.New(cfg)
+
+	ctx, rootCancel := context.WithCancel(context.Background())
+	defer rootCancel()
+
+	go func() {
+		if err := chkr.Run(ctx); err != nil {
+			slog.Error("checker-exited", "err", err)
+		}
+	}()
+
+	// ---- gRPC server --------------------------------------------------------
+	lis, err := net.Listen("tcp", *grpcAddr)
+	if err != nil {
+		return fmt.Errorf("listen %s: %w", *grpcAddr, err)
+	}
+	srv := grpc.NewServer()
+	grpcapi.RegisterHealthCheckerServer(srv, grpcapi.NewServer(chkr))
+	slog.Info("grpc-listening", "addr", *grpcAddr)
+
+	go func() {
+		if err := srv.Serve(lis); err != nil {
+			slog.Error("grpc-serve-error", "err", err)
+		}
+	}()
+
+	// ---- signal handling ----------------------------------------------------
+	sigCh := make(chan os.Signal, 1)
+	signal.Notify(sigCh, syscall.SIGHUP, syscall.SIGTERM, syscall.SIGINT)
+
+	for sig := range sigCh {
+		switch sig {
+		case syscall.SIGHUP:
+			slog.Info("config-reload-start")
+			newCfg, err := config.Load(*configPath)
+			if err != nil {
+				slog.Error("config-reload-error", "err", err)
+				continue
+			}
+			if err := chkr.Reload(ctx, newCfg); err != nil {
+				slog.Error("checker-reload-error", "err", err)
+				continue
+			}
+			slog.Info("config-reload-done", "vips", len(newCfg.VIPs))
+
+		case syscall.SIGTERM, syscall.SIGINT:
+			slog.Info("shutdown", "signal", sig)
+			rootCancel()
+			srv.GracefulStop()
+			return nil
+		}
+	}
+	return nil
+}
+
+// stringFlag declares a flag that falls back to an environment variable.
+func stringFlag(name, defaultVal, envKey, usage string) *string {
+	val := defaultVal
+	if v := os.Getenv(envKey); v != "" {
+		val = v
+	}
+	return flag.String(name, val, fmt.Sprintf("%s (env: %s)", usage, envKey))
+}