Lock DATA_DIR against a second instance (closes #201 )

Nothing stopped two processes opening the same DATA_DIR. Both open the same per-webhook databases, both run delivery recovery over the same rows, and both deliver: every pending delivery reaches the destination twice, from nothing worse than an overlapping deploy. The entry point now takes an exclusive advisory flock(2) on {DATA_DIR}/webhooker.lock before anything opens a database, and holds it for the process lifetime. A second process pointed at the same directory prints a message naming that directory and exits 1. The lock is the kernel's, not the file's, so a process killed with SIGKILL leaves a lock file that blocks nothing -- which is what a pidfile would get wrong. The file is never unlinked: doing so would let the next process lock a fresh inode while a third still held the old one. Acquisition lives in internal/datadir rather than in the server's fx graph, so any entry point touching DATA_DIR takes it the same way, and ErrLocked lets a caller tell a live deployment from any other failure. config.DataDir() resolves DATA_DIR once, for both the lock and Config, so the two cannot disagree. Regression coverage: a real second process is refused, and a restart after kill -9 succeeds with the stale lock file in place. github.com/gofrs/flock carries the lock; its own module minimums pull testify to v1.11.1 and golang.org/x/sys to v0.37.0.
2026-08-20 04:14:36 +00:00
9 changed files with 34 additions and 545 deletions
--- a/README.md
+++ b/README.md
@@ -107,26 +107,14 @@ TTY detection, and security headers are always applied.
 | `DATA_DIR`              | Directory for all SQLite databases  | `/var/lib/webhooker` |
 | `DEBUG`                 | Enable debug logging                | `false`  |
 | `MAINTENANCE_MODE`      | Report `maintenanceMode: true` in the healthcheck JSON. It does not change how any request is served — no maintenance page exists | `false`  |
-| `METRICS_USERNAME`      | Basic auth username for `/metrics`. Must be set together with `METRICS_PASSWORD`; one without the other fails startup | `""`     |
-| `METRICS_PASSWORD`      | Basic auth password for `/metrics`. Must be set together with `METRICS_USERNAME`; one without the other fails startup | `""`     |
+| `METRICS_USERNAME`      | Basic auth username for `/metrics`  | `""`     |
+| `METRICS_PASSWORD`      | Basic auth password for `/metrics`  | `""`     |
 | `SENTRY_DSN`            | Sentry error reporting DSN          | `""`     |
 | `RETENTION_SWEEP_INTERVAL` | How often the retention reaper and archive sweeper run (Go duration, must be positive) | `1h` |
 | `SESSION_IDLE_TIMEOUT`  | Idle session timeout (Go duration)  | `24h`    |
 | `RECEIVER_RATE_LIMIT`   | Receiver requests/minute per IP per entrypoint (10x that per IP across the route) | `120` |
 | `TRUSTED_PROXIES`       | CIDRs whose forwarded headers are trusted (unset: all clients behind a proxy share one rate-limit bucket; a correct login password is never throttled either way) | `""` (none) |

-#### Metrics credentials
-
-`METRICS_USERNAME` and `METRICS_PASSWORD` are set together or not at
-all. With both set, `/metrics` is served behind basic auth. With
-neither set, the route is not registered and returns 404. With one set
-and the other empty or unset, the process refuses to start and exits
-non-zero with an error naming both variables — mounting the endpoint
-on the username alone would publish it behind a password that is the
-empty string, and quietly withholding it would deny an endpoint that
-was asked for. The `hasMetricsAuth` field in the startup log and the
-existence of the route are the same value, so they cannot disagree.
-
 #### Single-instance lock

 Exactly one webhooker process may use a `DATA_DIR` at a time. Two
@@ -153,14 +141,6 @@ the old one.

 To run two webhookers on one host, give each its own `DATA_DIR`.

-`flock(2)` is host-local and per-inode: it arbitrates between processes
-and containers sharing a volume or bind mount on one machine, but not
-between hosts on a network filesystem, and a `DATA_DIR` inside a
-container's own writable layer is not shared with anything. On a
-filesystem that refuses `flock` outright, startup fails closed — the
-process reports the error and refuses to start rather than running
-unlocked.
-
 #### Trusted proxies

 `TRUSTED_PROXIES` is a comma-separated list of CIDR blocks (a bare
@@ -1730,7 +1710,7 @@ abuse limit later; they are tracked as future work.

 | Method | Path       | Description |
 | ------ | ---------- | ----------- |
-| `GET`  | `/metrics` | Prometheus metrics, behind basic auth. The route is registered only when `METRICS_USERNAME` and `METRICS_PASSWORD` are both set; with neither set it does not exist and returns 404, and with only one set the process refuses to start |
+| `GET`  | `/metrics` | Prometheus metrics, behind basic auth. The route is registered only when `METRICS_USERNAME` is set; otherwise it does not exist and returns 404 |

 #### API (Planned)

@@ -1887,8 +1867,7 @@ Applied to all routes in this order:
   Permissions-Policy)
 3. **Logging** — Structured request logging (method, URL, status,
   latency, remote IP, user agent, request ID)
-4. **Metrics** — Prometheus HTTP metrics (if `METRICS_USERNAME` and
-   `METRICS_PASSWORD` are both set)
+4. **Metrics** — Prometheus HTTP metrics (if `METRICS_USERNAME` is set)
 5. **CORS** — Cross-origin resource sharing headers
 6. **Timeout** — 60-second request timeout
 7. **Recoverer** — Panic recovery: one `ERROR` record through
@@ -1920,9 +1899,8 @@ being read and without reaching CSRF, the route group's remaining
 middleware, or the handler. It is not rejected before *any* other
 middleware, though: the global entries listed above all run first, so
 such a request is still logged and given the security headers — and
-counted in the metrics, on a deployment where the `/metrics`
-credentials are set and the Metrics middleware is therefore registered
-at all. The
+counted in the metrics, on a deployment where `METRICS_USERNAME` is
+set and the Metrics middleware is therefore registered at all. The
 rejection itself is logged at `WARN` with the method, path and
 declared length. A chunked request, or
 one that lies about its length, is hard-capped by
--- a/internal/config/config.go
+++ b/internal/config/config.go
@@ -75,16 +75,6 @@ var ErrInvalidPort = errors.New("invalid port")
 // nor a bare IP address.
 var ErrInvalidCIDR = errors.New("invalid CIDR")

-// ErrIncompleteMetricsAuth is returned when exactly one of
-// METRICS_USERNAME and METRICS_PASSWORD carries a value. Neither
-// fallback is acceptable: serving /metrics on the username alone
-// publishes an endpoint whose password is the empty string, and
-// silently leaving it unmounted withholds an endpoint the operator
-// asked for. Half-set is a configuration error, so startup fails.
-var ErrIncompleteMetricsAuth = errors.New(
-	"incomplete metrics credentials",
-)
-
 //nolint:revive // ConfigParams is a standard fx naming convention.
 type ConfigParams struct {
 	fx.In
@@ -142,21 +132,6 @@ func (c *Config) IsProd() bool {
 	return c.Environment == EnvironmentProd
 }

-// MetricsAuthEnabled reports whether /metrics is served behind basic
-// auth. It is the only answer to that question in the codebase: the
-// route mount, the Prometheus recording middleware and the startup
-// log's hasMetricsAuth field all read this one method, so the log
-// cannot report auth as off while the route is mounted.
-//
-// It requires both credentials rather than the username alone.
-// loadFromEnv already rejects a half-set pair, but a Config built in
-// code bypasses that, and the failure mode this guards is an endpoint
-// mounted with a credential map whose only password is the empty
-// string.
-func (c *Config) MetricsAuthEnabled() bool {
-	return c.MetricsUsername != "" && c.MetricsPassword != ""
-}
-
 // envString returns the value of the named environment variable,
 // or an empty string if not set.
 func envString(key string) string {
@@ -371,30 +346,6 @@ func envPrefixList(key string) ([]netip.Prefix, error) {
 	return prefixes, nil
 }

-// resolveMetricsAuth reads the /metrics basic-auth credentials and
-// rejects a half-set pair, naming both variables either way. The
-// error carries neither value: the password is a secret.
-func resolveMetricsAuth() (string, string, error) {
-	username := envString("METRICS_USERNAME")
-	password := envString("METRICS_PASSWORD")
-
-	if (username == "") == (password == "") {
-		return username, password, nil
-	}
-
-	set, empty := "METRICS_USERNAME", "METRICS_PASSWORD"
-	if username == "" {
-		set, empty = empty, set
-	}
-
-	return "", "", fmt.Errorf(
-		"%w: %s is set but %s is empty; METRICS_USERNAME and "+
-			"METRICS_PASSWORD must both be set to serve /metrics, "+
-			"or both be empty to leave it unmounted",
-		ErrIncompleteMetricsAuth, set, empty,
-	)
-}
-
 // resolveEnvironment reads WEBHOOKER_ENVIRONMENT, defaulting to
 // dev, and rejects unrecognised values.
 func resolveEnvironment() (string, error) {
@@ -472,18 +423,13 @@ func loadFromEnv() (*Config, error) {
 		return nil, err
 	}

-	metricsUsername, metricsPassword, err := resolveMetricsAuth()
-	if err != nil {
-		return nil, err
-	}
-
 	return &Config{
 		DataDir:                DataDir(),
 		Debug:                  debug,
 		MaintenanceMode:        maintenanceMode,
 		Environment:            environment,
-		MetricsUsername:        metricsUsername,
-		MetricsPassword:        metricsPassword,
+		MetricsUsername:        envString("METRICS_USERNAME"),
+		MetricsPassword:        envString("METRICS_PASSWORD"),
 		Port:                   port,
 		SentryDSN:              envString("SENTRY_DSN"),
 		RetentionSweepInterval: retentionSweepInterval,
@@ -575,7 +521,8 @@ func New(lc fx.Lifecycle, params ConfigParams) (*Config, error) {
 		"receiverRateLimit", s.ReceiverRateLimit,
 		"trustedProxies", len(s.TrustedProxies),
 		"hasSentryDSN", s.SentryDSN != "",
-		"hasMetricsAuth", s.MetricsAuthEnabled(),
+		"hasMetricsAuth",
+		s.MetricsUsername != "" && s.MetricsPassword != "",
 	)

 	s.warnSharedRateLimitBucket(log)
--- a/internal/config/config_test.go
+++ b/internal/config/config_test.go
@@ -26,12 +26,6 @@ const (
 	// cidrPrivateV4 is the sample trusted-proxy block the
 	// TRUSTED_PROXIES cases are built from.
 	cidrPrivateV4 = "10.0.0.0/8"
-
-	// metricsAuthValue is the sample METRICS_PASSWORD the metrics
-	// credential cases are built from. It is asserted absent from
-	// the startup error, so it must not be a substring of either
-	// variable name that error prints.
-	metricsAuthValue = "s3cret"
 )

 func TestEnvironmentConfig(t *testing.T) {
@@ -762,168 +756,3 @@ func TestSharedRateLimitBucketWarning(t *testing.T) {
 		})
 	}
 }
-
-// metricsEnv describes what one subtest below puts in the
-// environment for a single METRICS_ variable. A variable that is
-// set to the empty string and one that is not set at all are
-// distinct inputs here, because the reported bug arrived through
-// the first of them.
-type metricsEnv struct {
-	set   bool
-	value string
-}
-
-// unset leaves the variable out of the environment entirely.
-func unset() metricsEnv {
-	return metricsEnv{set: false, value: ""}
-}
-
-// setTo sets the variable, including to the empty string.
-func setTo(value string) metricsEnv {
-	return metricsEnv{set: true, value: value}
-}
-
-// metricsAuthCase is one row of the table in TestMetricsAuthConfig,
-// named so the table can live in its own function and keep the test
-// itself short.
-type metricsAuthCase struct {
-	name        string
-	username    metricsEnv
-	password    metricsEnv
-	expectError bool
-	expectAuth  bool
-}
-
-// metricsAuthCases enumerates every combination of the two
-// credentials, counting "set to the empty string" and "not set at
-// all" as separate inputs on each side.
-func metricsAuthCases() []metricsAuthCase {
-	return []metricsAuthCase{
-		{
-			name:     "both unset leaves metrics unmounted",
-			username: unset(),
-			password: unset(),
-		},
-		{
-			name:     "both empty leaves metrics unmounted",
-			username: setTo(""),
-			password: setTo(""),
-		},
-		{
-			name:       "both set enables metrics auth",
-			username:   setTo("metrics"),
-			password:   setTo(metricsAuthValue),
-			expectAuth: true,
-		},
-		{
-			name:        "username with unset password fails",
-			username:    setTo("metrics"),
-			password:    unset(),
-			expectError: true,
-		},
-		{
-			name:        "username with empty password fails",
-			username:    setTo("metrics"),
-			password:    setTo(""),
-			expectError: true,
-		},
-		{
-			name:        "password with unset username fails",
-			username:    unset(),
-			password:    setTo(metricsAuthValue),
-			expectError: true,
-		},
-		{
-			name:        "password with empty username fails",
-			username:    setTo(""),
-			password:    setTo(metricsAuthValue),
-			expectError: true,
-		},
-	}
-}
-
-// TestMetricsAuthConfig covers every combination of METRICS_USERNAME
-// and METRICS_PASSWORD. Either both carry a value, in which case
-// /metrics is served behind basic auth, or neither does, in which
-// case the route is never mounted. One without the other is a
-// startup error rather than a fallback: mounting on the username
-// alone published /metrics behind a credential map that accepted an
-// empty password, which is the defect this test exists to pin. See
-// https://git.eeqj.de/sneak/webhooker/issues/205.
-func TestMetricsAuthConfig(t *testing.T) {
-	for _, tt := range metricsAuthCases() {
-		t.Run(tt.name, func(t *testing.T) {
-			// Cannot use t.Parallel() here because t.Setenv
-			// is incompatible with parallel subtests.
-			if tt.username.set {
-				t.Setenv("METRICS_USERNAME", tt.username.value)
-			} else {
-				require.NoError(
-					t, os.Unsetenv("METRICS_USERNAME"),
-				)
-			}
-
-			if tt.password.set {
-				t.Setenv("METRICS_PASSWORD", tt.password.value)
-			} else {
-				require.NoError(
-					t, os.Unsetenv("METRICS_PASSWORD"),
-				)
-			}
-
-			if tt.expectError {
-				assertMetricsAuthRejected(t)
-
-				return
-			}
-
-			assertMetricsAuthAccepted(t, tt.expectAuth)
-		})
-	}
-}
-
-// assertMetricsAuthRejected requires that fx refused to build the
-// graph, that the failure is ErrIncompleteMetricsAuth, and that the
-// operator is told both variable names — the point of failing here
-// rather than degrading is that the message says what to fix.
-func assertMetricsAuthRejected(t *testing.T) {
-	t.Helper()
-
-	var cfg *config.Config
-
-	app := fx.New(
-		fx.NopLogger,
-		fx.Provide(globals.New, logger.New, config.New),
-		fx.Populate(&cfg),
-	)
-
-	err := app.Err()
-	require.Error(t, err)
-	require.ErrorIs(t, err, config.ErrIncompleteMetricsAuth)
-	assert.Contains(t, err.Error(), "METRICS_USERNAME")
-	assert.Contains(t, err.Error(), "METRICS_PASSWORD")
-	// The password is a secret and must not reach a startup error.
-	assert.NotContains(t, err.Error(), metricsAuthValue)
-}
-
-// assertMetricsAuthAccepted requires that startup succeeded and that
-// MetricsAuthEnabled — the single value the /metrics mount and the
-// startup log both read — reports what the environment asked for.
-func assertMetricsAuthAccepted(t *testing.T, expectAuth bool) {
-	t.Helper()
-
-	var cfg *config.Config
-
-	app := fxtest.New(
-		t,
-		fx.Provide(globals.New, logger.New, config.New),
-		fx.Populate(&cfg),
-	)
-	require.NoError(t, app.Err())
-
-	app.RequireStart()
-
-	defer app.RequireStop()
-
-	assert.Equal(t, expectAuth, cfg.MetricsAuthEnabled())
-}
--- a/internal/datadir/lock.go
+++ b/internal/datadir/lock.go
@@ -82,8 +82,8 @@ func Acquire(dir string) (*Lock, error) {
 	}

 	if !held {
-		// A no-op on flock v0.13.0, which closes its own descriptor on
-		// a failed TryLock; kept so no version can leak one.
+		// TryLock leaves the descriptor open when it fails to take
+		// the lock, so it has to be closed explicitly.
 		_ = fl.Close()

 		return nil, fmt.Errorf(
--- a/internal/server/http.go
+++ b/internal/server/http.go
@@ -43,7 +43,10 @@ func (s *Server) serveUntilShutdown() {
 	err := s.httpServer.ListenAndServe()
 	if err != nil && !errors.Is(err, http.ErrServerClosed) {
 		s.log.Error("listen error", "error", err)
-		s.shutdownOnListenFailure()
+
+		if s.cancelFunc != nil {
+			s.cancelFunc()
+		}
 	}
 }

--- a/internal/server/listen_failure_test.go
+++ b/internal/server/listen_failure_test.go
@@ -1,95 +0,0 @@
-package server_test
-
-import (
-	"context"
-	"net"
-	"testing"
-	"time"
-
-	"github.com/stretchr/testify/require"
-	"go.uber.org/fx"
-	"sneak.berlin/go/webhooker/internal/globals"
-	"sneak.berlin/go/webhooker/internal/server"
-)
-
-// listenFailureDeadline is how long the app gets to give up after a
-// listen it cannot satisfy. The defect this pins left the process
-// reporting RUNNING for 183 seconds with nothing bound; a bind error
-// is known instantly, so anything past a moment here is that defect
-// back.
-const listenFailureDeadline = 2 * time.Second
-
-// lifecycleTimeout bounds the app's start and stop sequences so a
-// wedged hook fails the test instead of hanging it.
-const lifecycleTimeout = 15 * time.Second
-
-// TestListenFailure_ShutsDownTheApp pins that a listener the server
-// cannot bind terminates the application with a non-zero status.
-//
-// The fx OnStart hook returns as soon as the serving goroutine is
-// spawned, so a bind failure is discovered after fx has already
-// reported RUNNING. Nothing else in the graph observes it, and the
-// process used to stay alive with no listener: down, but indis-
-// tinguishable from healthy to systemd's Restart=on-failure and to
-// Docker's restart policies, which is the state this test exists to
-// keep from returning.
-//
-// The port is occupied by a listener this test holds open, on a
-// kernel-chosen port, so the failure is the real EADDRINUSE the
-// operator hits when a second instance starts. Loopback is enough to
-// collide with the server's wildcard bind: a listening socket on a
-// specific address blocks the wildcard from claiming the same port.
-func TestListenFailure_ShutsDownTheApp(t *testing.T) {
-	t.Parallel()
-
-	var listenCfg net.ListenConfig
-
-	occupied, err := listenCfg.Listen(
-		t.Context(), "tcp", "127.0.0.1:0",
-	)
-	require.NoError(t, err)
-
-	t.Cleanup(func() { _ = occupied.Close() })
-
-	addr, ok := occupied.Addr().(*net.TCPAddr)
-	require.True(t, ok, "listener is not TCP")
-
-	// The collaborators come from the wired graph rather than stubs,
-	// so the Server under test is the one that ships. Only the port
-	// is test-specific.
-	env := newTestEnv(t)
-	env.cfg.Port = addr.Port
-
-	app := fx.New(
-		fx.NopLogger,
-		fx.Supply(env.log, env.cfg, env.mw, env.hnd),
-		fx.Provide(globals.New, server.New),
-		fx.Invoke(func(*server.Server) {}),
-	)
-
-	startCtx, cancelStart := context.WithTimeout(
-		context.Background(), lifecycleTimeout,
-	)
-	defer cancelStart()
-
-	require.NoError(t, app.Start(startCtx))
-
-	select {
-	case sig := <-app.Wait():
-		require.Equal(
-			t, server.ListenFailureExitCode, sig.ExitCode,
-			"listen failure must exit non-zero",
-		)
-	case <-time.After(listenFailureDeadline):
-		t.Fatal("listen failure left the app running")
-	}
-
-	// The stop sequence still has to complete: the fix must reach
-	// shutdown through fx rather than around it.
-	stopCtx, cancelStop := context.WithTimeout(
-		context.Background(), lifecycleTimeout,
-	)
-	defer cancelStop()
-
-	require.NoError(t, app.Stop(stopCtx))
-}
--- a/internal/server/routes.go
+++ b/internal/server/routes.go
@@ -55,11 +55,8 @@ func (s *Server) setupGlobalMiddleware() {
 	s.router.Use(s.mw.SecurityHeaders())
 	s.router.Use(s.mw.Logging())

-	// Metrics recording middleware, registered only when the
-	// endpoint that exposes what it records is served. The
-	// condition is the same MetricsAuthEnabled the /metrics mount
-	// in setupRoutes reads.
-	if s.params.Config.MetricsAuthEnabled() {
+	// Metrics middleware (only if credentials are configured)
+	if s.params.Config.MetricsUsername != "" {
 		s.router.Use(s.mw.Metrics())
 	}

@@ -106,14 +103,8 @@ func (s *Server) setupRoutes() {
 		s.h.HandleHealthCheck(),
 	)

-	// Authenticated /metrics route. The condition is
-	// Config.MetricsAuthEnabled and never the username alone: a
-	// username with an empty password would otherwise mount the
-	// endpoint behind a credential map that accepts an empty
-	// password. Config rejects that combination at startup, and
-	// this reads the same value the startup log reports, so the
-	// two cannot disagree about whether the route exists.
-	if s.params.Config.MetricsAuthEnabled() {
+	// set up authenticated /metrics route:
+	if s.params.Config.MetricsUsername != "" {
 		s.router.Group(func(r chi.Router) {
 			r.Use(s.mw.MetricsAuth())
 			r.Get(
--- a/internal/server/routes_test.go
+++ b/internal/server/routes_test.go
@@ -34,13 +34,6 @@ import (
 // the CSRF middleware executed.
 const csrfCookieName = "_gorilla_csrf"

-const (
-	// metricsUser and metricsAuthValue are the /metrics basic-auth
-	// credentials the metrics routing tests below configure.
-	metricsUser      = "metrics"
-	metricsAuthValue = "s3cret"
-)
-
 type noopNotifier struct{}

 func (n *noopNotifier) Notify([]delivery.Task) {}
@@ -76,23 +69,9 @@ type testEnv struct {
 func newTestEnv(t *testing.T) *testEnv {
 	t.Helper()

-	return newTestEnvWithConfig(t, &config.Config{
-		DataDir:     t.TempDir(),
-		Environment: config.EnvironmentDev,
-	})
-}
-
-// newTestEnvWithConfig is newTestEnv over a caller-supplied Config,
-// for the routes whose existence the configuration decides. The same
-// pointer reaches the router and every middleware, so a test cannot
-// accidentally configure one and not the other.
-func newTestEnvWithConfig(
-	t *testing.T, cfg *config.Config,
-) *testEnv {
-	t.Helper()
-
 	var (
 		log   *logger.Logger
+		cfg   *config.Config
 		mw    *middleware.Middleware
 		hnd   *handlers.Handlers
 		sess  *session.Session
@@ -105,7 +84,12 @@ func newTestEnvWithConfig(
 		fx.Provide(
 			globals.New,
 			logger.New,
-			func() *config.Config { return cfg },
+			func() *config.Config {
+				return &config.Config{
+					DataDir:     t.TempDir(),
+					Environment: config.EnvironmentDev,
+				}
+			},
 			database.New,
 			database.NewWebhookDBManager,
 			healthcheck.New,
@@ -115,7 +99,7 @@ func newTestEnvWithConfig(
 			middleware.New,
 			handlers.New,
 		),
-		fx.Populate(&log, &mw, &hnd, &sess, &db, &dbMgr),
+		fx.Populate(&log, &cfg, &mw, &hnd, &sess, &db, &dbMgr),
 	)
 	app.RequireStart()
 	t.Cleanup(app.RequireStop)
@@ -673,119 +657,3 @@ func TestSourceLogsBody_OtherUser404s(t *testing.T) {
 	assert.Equal(t, http.StatusSeeOther, anon.Code)
 	assert.Equal(t, "/pages/login", anon.Header().Get("Location"))
 }
-
-// metricsConfig is a Config differing from the routing default only
-// in the two /metrics credentials.
-func metricsConfig(
-	t *testing.T, username, password string,
-) *config.Config {
-	t.Helper()
-
-	return &config.Config{
-		DataDir:         t.TempDir(),
-		Environment:     config.EnvironmentDev,
-		MetricsUsername: username,
-		MetricsPassword: password,
-	}
-}
-
-// metricsRequest asks the real router for /metrics with the given
-// basic-auth credentials, or with no Authorization header when
-// username is empty.
-func (e *testEnv) metricsRequest(
-	username, password string,
-) *httptest.ResponseRecorder {
-	req := httptest.NewRequestWithContext(
-		context.Background(), http.MethodGet, "/metrics", nil,
-	)
-
-	if username != "" {
-		req.SetBasicAuth(username, password)
-	}
-
-	w := httptest.NewRecorder()
-	e.router.ServeHTTP(w, req)
-
-	return w
-}
-
-// TestMetricsRouteUnmountedWithoutCredentials pins that with neither
-// credential configured the route does not exist, which is the
-// documented behaviour and the only valid way for /metrics to be
-// absent.
-func TestMetricsRouteUnmountedWithoutCredentials(t *testing.T) {
-	t.Parallel()
-
-	env := newTestEnvWithConfig(t, metricsConfig(t, "", ""))
-
-	assert.Equal(
-		t, http.StatusNotFound,
-		env.metricsRequest("", "").Code,
-	)
-}
-
-// TestMetricsRouteRequiresCredentials pins that with both credentials
-// configured the route exists and every request that does not carry
-// the configured pair is refused — including the empty password that
-// a half-set configuration used to make sufficient.
-func TestMetricsRouteRequiresCredentials(t *testing.T) {
-	t.Parallel()
-
-	env := newTestEnvWithConfig(
-		t, metricsConfig(t, metricsUser, metricsAuthValue),
-	)
-
-	assert.Equal(
-		t, http.StatusUnauthorized,
-		env.metricsRequest("", "").Code,
-		"no credentials must not reach the metrics handler",
-	)
-	assert.Equal(
-		t, http.StatusUnauthorized,
-		env.metricsRequest(metricsUser, "").Code,
-		"an empty password must not reach the metrics handler",
-	)
-	assert.Equal(
-		t, http.StatusUnauthorized,
-		env.metricsRequest(metricsUser, "wrong").Code,
-	)
-
-	ok := env.metricsRequest(metricsUser, metricsAuthValue)
-	assert.Equal(t, http.StatusOK, ok.Code)
-	assert.Contains(t, ok.Body.String(), "go_goroutines")
-}
-
-// TestMetricsRouteUnmountedOnHalfSetConfig pins the defect from
-// https://git.eeqj.de/sneak/webhooker/issues/205 at the routing
-// layer. Config rejects a half-set pair at startup, so this Config
-// cannot be reached from the environment; the assertion is that the
-// route tree does not publish an endpoint accepting an empty
-// password even when handed one anyway, because the mount and the
-// startup log's hasMetricsAuth read the same value.
-func TestMetricsRouteUnmountedOnHalfSetConfig(t *testing.T) {
-	t.Parallel()
-
-	for _, tc := range []struct {
-		name     string
-		username string
-		password string
-	}{
-		{name: "username only", username: metricsUser},
-		{name: "password only", password: metricsAuthValue},
-	} {
-		t.Run(tc.name, func(t *testing.T) {
-			t.Parallel()
-
-			cfg := metricsConfig(t, tc.username, tc.password)
-			env := newTestEnvWithConfig(t, cfg)
-
-			assert.False(t, cfg.MetricsAuthEnabled())
-			assert.Equal(
-				t, http.StatusNotFound,
-				env.metricsRequest(
-					tc.username, tc.password,
-				).Code,
-			)
-		})
-	}
-}
--- a/internal/server/server.go
+++ b/internal/server/server.go
@@ -50,13 +50,6 @@ const (
 	minSentryFlush = 250 * time.Millisecond
 )

-// ListenFailureExitCode is the status the process exits with when the
-// HTTP listener cannot be established, or dies for a reason other
-// than a requested shutdown. It must stay non-zero: systemd
-// `Restart=on-failure` and Docker's restart policies key off it, and a
-// zero exit would read as a deliberate stop.
-const ListenFailureExitCode = 1
-
 // SentryFlushBudget reports how long the Sentry flush may run when
 // remaining is the time left on the fx stop context after the HTTP
 // drain. sentry.Flush takes a bare duration and honours no context,
@@ -82,13 +75,13 @@ type ServerParams struct {
 	Config     *config.Config
 	Middleware *middleware.Middleware
 	Handlers   *handlers.Handlers
-	Shutdowner fx.Shutdowner
 }

 // Server is the main HTTP server that wires up routes and manages
 // graceful shutdown.
 type Server struct {
 	startupTime   time.Time
+	exitCode      int
 	sentryEnabled bool
 	log           *slog.Logger
 	cancelFunc    context.CancelFunc
@@ -166,12 +159,7 @@ func (s *Server) enableSentry() {
 	s.sentryEnabled = true
 }

-// serve installs the signal watcher, starts the listener and blocks
-// until the server's context is cancelled. The process exit status is
-// fx's to decide — from a signal, or from the code
-// shutdownOnListenFailure hands the Shutdowner — so this reports
-// nothing back to its caller.
-func (s *Server) serve() {
+func (s *Server) serve() int {
 	ctx, cancelFunc := context.WithCancel(context.Background())
 	s.cancelFunc = cancelFunc

@@ -197,30 +185,7 @@ func (s *Server) serve() {
 	<-ctx.Done()
 	// Shutdown is handled by the fx OnStop hook (cleanShutdown).
 	// Do not call cleanShutdown() here to avoid double invocation.
-}
-
-// shutdownOnListenFailure ends the application after the HTTP
-// listener failed. The fx OnStart hook returns as soon as the serving
-// goroutine is spawned, so nothing downstream of it ever learns that
-// the listen failed: fx reports RUNNING and the process sits alive
-// with nothing bound, which is invisible to systemd and Docker
-// restart policies. Asking the Shutdowner to stop the app with a
-// non-zero code is what turns that into a visible failure.
-//
-// The context cancel that follows only unwinds serve()'s own wait.
-// The shutdown itself runs through fx's normal stop sequence, so the
-// clean-shutdown drain in cleanShutdown is reached unchanged.
-func (s *Server) shutdownOnListenFailure() {
-	err := s.params.Shutdowner.Shutdown(
-		fx.ExitCode(ListenFailureExitCode),
-	)
-	if err != nil {
-		s.log.Error("shutdown request failed", "error", err)
-	}
-
-	if s.cancelFunc != nil {
-		s.cancelFunc()
-	}
+	return s.exitCode
 }

 func (s *Server) cleanupForExit() {
@@ -228,6 +193,9 @@ func (s *Server) cleanupForExit() {
 }

 func (s *Server) cleanShutdown(ctx context.Context) {
+	// initiate clean shutdown
+	s.exitCode = 0
+
 	ctxShutdown, shutdownCancel := context.WithTimeout(
 		ctx, ShutdownTimeout,
 	)