Serve /metrics from a registry of its own (closes #227)

The HTTP metrics recorder, the delivery collectors and the Go and
process collectors now register on one prometheus.Registry that fx
provides, instead of Prometheus's global default registry, and
/metrics serves that registry. A second metrics-enabled router in one
process, or the server tests run with -count=2, no longer panics on a
duplicate registration.

The middleware builds its recorder once, in New, so installing
Metrics() on more than one router over the same graph is also safe.
The scrape keeps the same series and labels, including go_*,
process_* and promhttp_metric_handler_*.

Model: opus-5-5

Dockerfile

@@ -88,9 +88,7 @@ RUN CGO_ENABLED=1 make build VERSION="$VERSION" GO_LDFLAGS='-extldflags "-static
 # alpine:3.21, 2026-03-17
 FROM alpine:3.21@sha256:c3f8e73fdb79deaebaa2037150150191b9dcbfba68b4a46d70103204c53f4709
 
-# su-exec 0.2-r3 (Alpine 3.21), 2026-09-29: the entrypoint runs the app
-# as webhooker with it.
-RUN apk --no-cache add ca-certificates su-exec=0.2-r3
+RUN apk --no-cache add ca-certificates
 
 # Create non-root user
 RUN addgroup -g 1000 -S webhooker && \
@@ -101,17 +99,13 @@ WORKDIR /app
 # Copy binary from builder
 COPY --from=builder /build/bin/webhooker /app/webhooker
 
-# Not under /app, which belongs to webhooker: this script runs as root.
-COPY deploy/docker-entrypoint.sh /usr/local/bin/docker-entrypoint.sh
-
 # Create data directory for all SQLite databases (main app DB +
 # per-webhook event DBs). DATA_DIR defaults to /var/lib/webhooker.
 RUN mkdir -p /var/lib/webhooker
 
 RUN chown -R webhooker:webhooker /app /var/lib/webhooker
 
-# No USER: the entrypoint starts as root to make the data directory
-# webhooker's, then runs the app as webhooker.
+USER webhooker
 
 EXPOSE 8080
 
@@ -130,5 +124,4 @@ ENV BIND_ADDRESS=0.0.0.0
 HEALTHCHECK --interval=30s --timeout=3s --start-period=5s --retries=3 \
     CMD wget --no-verbose --tries=1 --spider http://localhost:8080/.well-known/healthcheck || exit 1
 
-ENTRYPOINT ["/usr/local/bin/docker-entrypoint.sh"]
 CMD ["/app/webhooker"]

README.md

@@ -538,12 +538,6 @@ its Argon2id hash. There is no second account and no forgot-password
 flow, so the banner and the reset command below are the only two ways
 in.
 
-A start that finds no `webhooker.db` in `DATA_DIR` also logs
-`created a new, empty database` at `WARN`, with the file's path,
-shortly before the banner. On a deployment that has run before, that
-line means `DATA_DIR` was empty, most often because its volume is not
-mounted.
-
 #### Recovering a lost admin password
 
 `webhooker resetpw` sets an existing account's password from the
@@ -558,9 +552,8 @@ printf '%s' "$NEW_PASSWORD" | \
     DATA_DIR=/var/lib/webhooker webhooker resetpw admin
 ```
 
-In a container it is the same binary. The image's `CMD` is
-`/app/webhooker`, and a command given to `docker run` replaces all of
-it, so the whole command has to be given:
+In a container it is the same binary, which the image sets as `CMD`
+rather than `ENTRYPOINT`, so the whole command has to be given:
 
 ```bash
 docker run --rm -v webhooker-data:/var/lib/webhooker \
@@ -697,22 +690,38 @@ those three values rather than trusting the figure. Measured at 65s on
 Docker 29.7.2.) A container `unhealthy` with `connection refused` in
 its health log, or a published port that resets connections, is this.
 
-The app runs as a non-root user (`webhooker`, UID 1000), exposes port
-8080, and includes a health check against `/.well-known/healthcheck`.
-The `/var/lib/webhooker` volume holds all SQLite databases: the main
-application database (`webhooker.db`), the per-webhook event databases
-(`events-{uuid}.db`), and any archive databases written by `database`
-targets (`archive-{uuid}.db`). Mount this as a persistent volume to
-preserve data across container restarts.
+The container runs as a non-root user (`webhooker`, UID 1000), exposes
+port 8080, and includes a health check against
+`/.well-known/healthcheck`. The `/var/lib/webhooker` volume holds all
+SQLite databases: the main application database (`webhooker.db`), the
+per-webhook event databases (`events-{uuid}.db`), and any archive
+databases written by `database` targets (`archive-{uuid}.db`). Mount
+this as a persistent volume to preserve data across container
+restarts.
 
-**The container sets its data directory's owner and mode itself
-before the app starts**, so a host directory can be mounted as it is,
-whoever owns it. The image's `ENTRYPOINT`,
-`deploy/docker-entrypoint.sh`, starts as root, creates `DATA_DIR` if
-it is missing, gives the directory and anything in it that belongs to
-another user to `webhooker`, sets the directory to `0750`, and only
-then runs the app as `webhooker`. Started with `--user`, it changes
-nothing and runs the app as that user.
+**The bind-mounted directory must be owned by UID 1000, or the
+container does not start.** Docker creates a `-v` source path that
+does not exist yet as `root:root`, and the process runs as UID 1000,
+so it cannot take its `DATA_DIR` lock:
+
+```
+webhooker: locking data directory /var/lib/webhooker: open
+/var/lib/webhooker/webhooker.lock: permission denied
+```
+
+It exits non-zero at that point, before opening any database. Create
+the directory ahead of the first `docker run`:
+
+```bash
+mkdir -p /path/to/data
+chown 1000:1000 /path/to/data
+chmod 750 /path/to/data
+```
+
+The same `chown` is what a restore needs — see step 4 of
+[Restore](#restore). A **named volume** does not have this problem:
+Docker copies the image's ownership onto a volume it initializes, and
+the image creates `/var/lib/webhooker` owned by `webhooker`.
 
 **The file modes are not yours to set, and do not depend on the
 directory.** `webhooker.db` holds target configuration in plaintext —
@@ -720,10 +729,13 @@ bearer tokens, API keys, Slack webhook URLs — along with the session
 encryption key, so webhooker creates every SQLite file it owns `0600`:
 each database and both of its `-wal` and `-shm` sidecars, across all
 three tiers. Files an earlier build left `0644` are tightened when
-they are opened. The directory's `0750` is defence in depth — it stops
-other local users listing the directory and learning your webhook
-UUIDs from the `events-{uuid}.db` filenames — not the barrier
-protecting the credentials.
+they are opened. A `DATA_DIR` webhooker creates itself is `0750`, but
+a bind mount supplies its own directory and Docker's default for one
+it creates is `0755`; the `0600` files hold there regardless. The
+`chmod 750` above is defence in depth — it stops other local users
+listing the directory and learning your webhook UUIDs from the
+`events-{uuid}.db` filenames — not the barrier protecting the
+credentials.
 
 ### Running under upaas
 
@@ -739,6 +751,17 @@ repository's `Dockerfile` and runs it. The app needs:
   app name, port `8080`. Leave `PORT` unset: the image's health check
   probes `8080`.
 - **Volume:** one host directory mounted at `/var/lib/webhooker`.
+  upaas bind-mounts the host path it is given and does not create it,
+  and the container does not start unless UID 1000 owns it (see
+  [Running with Docker](#running-with-docker)). Create it before the
+  first deploy:
+
+    ```bash
+    mkdir -p /path/to/data
+    chown 1000:1000 /path/to/data
+    chmod 750 /path/to/data
+    ```
+
 - **Environment variables:**
     - `WEBHOOKER_ENVIRONMENT=prod`
     - `TRUSTED_PROXIES`: your reverse proxy's address on that Docker
@@ -997,12 +1020,12 @@ done
 `.backup` reads through the WAL and writes a single consistent file with
 no sidecars of its own, so the destination is complete as it stands.
 Two caveats. First, the runtime image is `alpine:3.21` with only
-`ca-certificates` and `su-exec` added — the `sqlite3` CLI is **not** in
-it, so run this on the host against the volume path, or from a
-throwaway container that mounts the volume. Second, each file is
-captured at its own instant, so a webhook created or an event delivered
-between two files being copied lands in one and not the other. If you
-need the whole set coherent as of a single moment, stop the service.
+`ca-certificates` added — the `sqlite3` CLI is **not** in it, so run
+this on the host against the volume path, or from a throwaway container
+that mounts the volume. Second, each file is captured at its own
+instant, so a webhook created or an event delivered between two files
+being copied lands in one and not the other. If you need the whole set
+coherent as of a single moment, stop the service.
 
 Note that `sqlite3 <db> .dump` is **not** one of these procedures: it is
 an export, it holds a read transaction open for as long as it runs, and
@@ -1056,11 +1079,21 @@ with any `-wal`/`-shm` beside it, or wait until there are none.
    archive not opened since a crash. A copy salvaged from a crashed
    instance has them for everything, and needs all of them.
 
-4. Start the service. The container gives the directory and the
-   restored files to the `webhooker` user before the app starts,
-   whoever restored them (see
-   [Running with Docker](#running-with-docker)). `AutoMigrate` runs
-   against each restored database as it is opened.
+4. **Fix ownership.** The container runs as the non-root `webhooker`
+   user, UID 1000 / GID 1000. Restored files must be owned by (or
+   writable by) that UID, and so must the directory itself — SQLite
+   creates the `-wal` and `-shm` sidecars beside the database, so a
+   writable file inside a directory it cannot write is not enough:
+
+    ```bash
+    chown -R 1000:1000 /path/to/data
+    ```
+
+    Restoring as `root` on the host and forgetting this step is the
+    usual way a restore fails.
+
+5. Start the service. `AutoMigrate` runs against each restored database
+   as it is opened.
 
 ### Upgrades
 
@@ -3038,11 +3071,7 @@ check, see [The login endpoint](#the-login-endpoint).
 - Prometheus metrics behind basic auth
 - Static assets embedded in binary (no filesystem access needed at
   runtime)
-- The app runs as the non-root `webhooker` user (UID 1000) in the
-  container. The image sets no `USER`, so these run as root: the
-  `ENTRYPOINT` script, which sets the data directory's owner and mode
-  before the app starts; the image's health check; and `docker exec`,
-  unless given `--user`
+- Container runs as non-root user (UID 1000)
 - GORM soft deletes on every entity that carries `BaseModel`, which is
   all of them but `Setting` (data preserved for audit)
 
@@ -3169,13 +3198,10 @@ version is fixed independently of the compiler's:
    `GO_LDFLAGS`, so neither can drop the `-X` that stamps the version.
    The version arrives as the `VERSION` build arg, since the context
    has no `.git` (see [Version stamping](#version-stamping)).
-3. **Runtime stage** (`alpine:3.21`) — copies the static binary and
-   `deploy/docker-entrypoint.sh`, creates the `/var/lib/webhooker`
-   directory for all SQLite databases, exposes port 8080, and includes
-   a health check against `/.well-known/healthcheck`. It sets no
-   `USER`: the `ENTRYPOINT` script starts as root, sets the data
-   directory's owner and mode, and runs the app as the non-root
-   `webhooker` user (UID 1000) through `su-exec`.
+3. **Runtime stage** (`alpine:3.21`) — copies the static binary,
+   creates the `/var/lib/webhooker` directory for all SQLite databases,
+   runs as the non-root `webhooker` user (UID 1000), exposes port 8080,
+   and includes a health check against `/.well-known/healthcheck`.
 
 The lint stage invokes `golangci-lint` directly rather than `make lint`:
 it is already the pinned linter image, and `make lint` builds
@@ -3254,5 +3280,3 @@ MIT
 ## Author
 
 [@sneak](https://sneak.berlin)
-
-

cmd/webhooker/main.go

@@ -16,6 +16,7 @@ import (
 	"sneak.berlin/go/webhooker/internal/handlers"
 	"sneak.berlin/go/webhooker/internal/healthcheck"
 	"sneak.berlin/go/webhooker/internal/logger"
+	"sneak.berlin/go/webhooker/internal/metrics"
 	"sneak.berlin/go/webhooker/internal/middleware"
 	"sneak.berlin/go/webhooker/internal/resetpw"
 	"sneak.berlin/go/webhooker/internal/server"
@@ -177,6 +178,10 @@ func newApp() *fx.App {
 			healthcheck.New,
 			session.New,
 			handlers.New,
+			// The registry /metrics serves, and the delivery
+			// collectors registered on it.
+			metrics.NewRegistry,
+			metrics.New,
 			middleware.New,
 			// The one SSRF guard both target-creation validation
 			// and the delivery dialer consult, so they cannot

deploy/docker-entrypoint.sh

@@ -1,22 +0,0 @@
-#!/bin/sh
-# deploy/docker-entrypoint.sh: the image's ENTRYPOINT. A bind-mounted
-# data directory keeps its owner from the host, often root, and the app
-# could not write to it. Started as root, this creates DATA_DIR if
-# needed, gives it and everything in it to webhooker, sets its mode, and
-# runs the command as webhooker, so the app never runs as root. Started
-# as another user, it only runs the command.
-set -eu
-
-main() {
-    if [ "$(id -u)" != 0 ]; then
-        exec "$@"
-    fi
-
-    dir="${DATA_DIR:-/var/lib/webhooker}"
-    mkdir -p "$dir"
-    find "$dir" ! -user webhooker -exec chown -h webhooker:webhooker {} +
-    chmod 750 "$dir"
-    exec su-exec webhooker "$@"
-}
-
-main "$@"

internal/database/bootstrap_banner_test.go

@@ -3,8 +3,6 @@ package database_test
 import (
 	"bytes"
 	"context"
-	"log/slog"
-	"path/filepath"
 	"strings"
 	"testing"
 
@@ -85,37 +83,3 @@ func TestFirstBoot_PrintsTheAdminPasswordAsABanner(t *testing.T) {
 		t, ok, "the printed password must open the seeded account",
 	)
 }
-
-// TestNewDatabase_IsLoggedWithItsPath is the log half of
-// https://git.eeqj.de/sneak/webhooker/issues/359. A DATA_DIR that is
-// unexpectedly empty boots exactly like a first start, so the start
-// that creates the database must say so, and where. Opening that
-// database again must not.
-func TestNewDatabase_IsLoggedWithItsPath(t *testing.T) {
-	t.Parallel()
-
-	dir := t.TempDir()
-
-	open := func() string {
-		var out bytes.Buffer
-
-		db, err := database.Open(dir, slog.New(slog.NewTextHandler(&out, nil)))
-		require.NoError(t, err)
-		require.NoError(t, db.Close())
-
-		return out.String()
-	}
-
-	const created = `level=WARN msg="created a new, empty database"`
-
-	first := open()
-	second := open()
-
-	assert.Contains(
-		t, first,
-		created+" path="+filepath.Join(dir, database.MainDBFileName),
-	)
-	assert.NotContains(
-		t, second, created, "an existing database is not new",
-	)
-}

internal/database/database.go

@@ -8,7 +8,6 @@ import (
 	"errors"
 	"fmt"
 	"io"
-	"io/fs"
 	"log/slog"
 	"os"
 	"path/filepath"
@@ -200,12 +199,6 @@ func (d *Database) connectTo(dataDir string) error {
 	// Construct the main application database path inside DATA_DIR.
 	dbPath := filepath.Join(dataDir, MainDBFileName)
 
-	// Checked before opening, which creates the file. A DATA_DIR that
-	// is unexpectedly empty -- its volume not mounted, say -- looks
-	// exactly like a first start, so a new database is a warning.
-	_, statErr := os.Stat(dbPath)
-	created := errors.Is(statErr, fs.ErrNotExist)
-
 	// Opened through OpenSQLite so this handle carries the same WAL
 	// journaling, busy timeout, immediate-transaction locking, and pool
 	// bounds as every other database file. See sqlite_open.go.
@@ -236,12 +229,7 @@ func (d *Database) connectTo(dataDir string) error {
 	}
 
 	d.db = db
-
-	if created {
-		d.log.Warn("created a new, empty database", "path", dbPath)
-	} else {
 	d.log.Info("connected to database", "path", dbPath)
-	}
 
 	// Run migrations
 	return d.migrate()

internal/delivery/engine.go

@@ -148,6 +148,7 @@ type EngineParams struct {
 	DBManager *database.WebhookDBManager
 	Logger    *logger.Logger
 	SSRFGuard *Guard
+	Metrics   *metrics.Set
 }
 
 // Engine processes queued deliveries in the background
@@ -167,10 +168,10 @@ type Engine struct {
 	retryCh    chan Task
 	workers    int
 
-	// mtr is the delivery metric set. Production wires the
-	// process-wide one; a test can substitute a set registered on
-	// a private registry so its assertions are not disturbed by
-	// deliveries other tests are making at the same time.
+	// mtr is the delivery metric set. Production wires the one
+	// registered on the registry /metrics serves; a test can
+	// substitute a set registered on a registry it holds, so it can
+	// gather what its own deliveries recorded.
 	mtr *metrics.Set
 
 	// targets maps each target type to its implementation.
@@ -204,7 +205,7 @@ func New(
 		deliveryCh: make(chan Task, deliveryChannelSize),
 		retryCh:    make(chan Task, retryChannelSize),
 		workers:    defaultWorkers,
-		mtr:        metrics.Default(),
+		mtr:        params.Metrics,
 	}
 
 	e.initTargets(&http.Client{

internal/delivery/export_test.go

@@ -9,6 +9,7 @@ import (
 	"net/url"
 	"time"
 
+	"github.com/prometheus/client_golang/prometheus"
 	"go.uber.org/fx"
 	"gorm.io/gorm"
 	"sneak.berlin/go/webhooker/internal/database"
@@ -389,7 +390,7 @@ func NewTestEngine(
 		deliveryCh: make(chan Task, deliveryChannelSize),
 		retryCh:    make(chan Task, retryChannelSize),
 		workers:    workers,
-		mtr:        metrics.Default(),
+		mtr:        metrics.New(prometheus.NewRegistry()),
 	}
 	e.initTargets(client)
 
@@ -404,7 +405,7 @@ func NewTestEngineSmallRetry(
 	e := &Engine{
 		log:     log,
 		retryCh: make(chan Task, 1),
-		mtr:     metrics.Default(),
+		mtr:     metrics.New(prometheus.NewRegistry()),
 	}
 	e.initTargets(nil)
 
@@ -427,7 +428,7 @@ func NewTestEngineWithDB(
 		deliveryCh: make(chan Task, deliveryChannelSize),
 		retryCh:    make(chan Task, retryChannelSize),
 		workers:    workers,
-		mtr:        metrics.Default(),
+		mtr:        metrics.New(prometheus.NewRegistry()),
 	}
 	e.initTargets(client)
 
@@ -435,8 +436,7 @@ func NewTestEngineWithDB(
 }
 
 // ExportSetMetrics substitutes the engine's metric set, so a test can
-// assert on collectors registered on a private registry instead of
-// the process-wide ones every other test is also moving.
+// assert on collectors registered on a registry it holds.
 func (e *Engine) ExportSetMetrics(mtr *metrics.Set) {
 	e.mtr = mtr
 }

internal/delivery/metrics_test.go

@@ -35,9 +35,8 @@ const (
 )
 
 // mIsolate gives the setup's engine a metric set registered on a
-// private registry. The process-wide collectors are moved by every
-// other delivery test running in parallel, so exact assertions are
-// only possible against a registry this test owns.
+// registry this test holds, so its exact assertions can gather from
+// it.
 func mIsolate(
 	t *testing.T, s iSetup,
 ) *prometheus.Registry {

internal/handlers/handlers.go

@@ -12,6 +12,7 @@ import (
 	"net/http"
 	"sync/atomic"
 
+	"github.com/prometheus/client_golang/prometheus"
 	"go.uber.org/fx"
 	"sneak.berlin/go/webhooker/internal/database"
 	"sneak.berlin/go/webhooker/internal/delivery"
@@ -61,6 +62,8 @@ type HandlersParams struct {
 	Notifier     delivery.Notifier
 	Evictor      delivery.WebhookEvictor
 	SSRFGuard    *delivery.Guard
+	Metrics      *metrics.Set
+	Registry     *prometheus.Registry
 }
 
 // Handlers provides HTTP handler methods for all application
@@ -122,7 +125,7 @@ func New(
 	s.mw = params.Middleware
 	s.notifier = params.Notifier
 	s.evictor = params.Evictor
-	s.mtr = metrics.Default()
+	s.mtr = params.Metrics
 	s.ssrf = params.SSRFGuard
 
 	// Parse all page templates once at startup

internal/handlers/handlers_test.go

@@ -20,6 +20,7 @@ import (
 	"sneak.berlin/go/webhooker/internal/handlers"
 	"sneak.berlin/go/webhooker/internal/healthcheck"
 	"sneak.berlin/go/webhooker/internal/logger"
+	"sneak.berlin/go/webhooker/internal/metrics"
 	"sneak.berlin/go/webhooker/internal/middleware"
 	"sneak.berlin/go/webhooker/internal/session"
 )
@@ -109,6 +110,8 @@ func newTestApp(
 			func(r *recordingEvictor) delivery.WebhookEvictor {
 				return r
 			},
+			metrics.NewRegistry,
+			metrics.New,
 			middleware.New,
 			delivery.NewGuard,
 			handlers.New,

internal/handlers/metrics.go

@@ -0,0 +1,20 @@
+package handlers
+
+import (
+	"net/http"
+
+	"github.com/prometheus/client_golang/prometheus/promhttp"
+)
+
+// HandleMetrics returns the Prometheus scrape handler for the
+// registry every collector in this process registers on. It is what
+// promhttp.Handler builds for the global default registry, including
+// the promhttp_metric_handler_* series that count scrapes, pointed at
+// that registry instead.
+func (s *Handlers) HandleMetrics() http.HandlerFunc {
+	reg := s.params.Registry
+
+	return promhttp.InstrumentMetricHandler(
+		reg, promhttp.HandlerFor(reg, promhttp.HandlerOpts{}),
+	).ServeHTTP
+}

internal/metrics/metrics.go

@@ -3,17 +3,17 @@
 // deliveries are attempted, how they end, how long they take, how
 // deep the queues are, and how many circuit breakers are open.
 //
-// The inbound HTTP metrics come from the go-http-metrics recorder in
-// internal/middleware and land on prometheus.DefaultRegisterer. These
-// collectors register there too, so both surfaces are gathered by the
-// one promhttp handler mounted on the authenticated /metrics route.
+// It also builds the registry the authenticated /metrics route
+// serves. These collectors, the inbound HTTP metrics recorded in
+// internal/middleware, and the Go runtime and process collectors all
+// register on that one registry, never on Prometheus's global default.
 package metrics
 
 import (
-	"sync"
 	"time"
 
 	"github.com/prometheus/client_golang/prometheus"
+	"github.com/prometheus/client_golang/prometheus/collectors"
 	"github.com/prometheus/client_golang/prometheus/promauto"
 	"sneak.berlin/go/webhooker/internal/database"
 )
@@ -57,25 +57,31 @@ var knownTargetTypes = []database.TargetType{
 	database.TargetTypeSlack,
 }
 
-// defaultSet is the process-wide metric set, registered on the same
-// registry the HTTP middleware and the /metrics handler already use.
-// It is built on first use rather than in an init so that a test
-// binary that never touches metrics never registers them.
+// NewRegistry returns the registry /metrics serves, carrying the Go
+// runtime and process collectors that Prometheus's global default
+// registry carries, so the go_* and process_* series stay in the
+// scrape.
 //
-//nolint:gochecknoglobals // one process-wide registration, by design
-var defaultSet = sync.OnceValue(func() *Set {
-	return New(prometheus.DefaultRegisterer)
-})
+// A registry of its own, rather than the global default, is what lets
+// two dependency graphs in one process — two tests, say — each
+// register their collectors without the second registration
+// panicking.
+func NewRegistry() *prometheus.Registry {
+	reg := prometheus.NewRegistry()
+	reg.MustRegister(
+		collectors.NewGoCollector(),
+		collectors.NewProcessCollector(
+			collectors.ProcessCollectorOpts{},
+		),
+	)
 
-// Default returns the process-wide metric set.
-func Default() *Set {
-	return defaultSet()
+	return reg
 }
 
 // Set is one registered group of webhooker's delivery collectors.
-// Production uses the single Default set; tests build their own
-// against a private registry so assertions are not disturbed by
-// deliveries other tests are making concurrently.
+// Production builds one on the registry /metrics serves; tests build
+// their own against a private registry so assertions are not
+// disturbed by deliveries other tests are making concurrently.
 type Set struct {
 	eventsReceived      prometheus.Counter
 	deliveryAttempts    *prometheus.CounterVec
@@ -93,7 +99,7 @@ type Set struct {
 // New registers a full set of delivery collectors on reg and returns
 // it. It panics if reg already holds them, which is the intended
 // behaviour for a duplicate registration.
-func New(reg prometheus.Registerer) *Set {
+func New(reg *prometheus.Registry) *Set {
 	factory := promauto.With(reg)
 
 	s := &Set{

internal/middleware/export_test.go

@@ -10,8 +10,7 @@ import (
 
 // MetricsMiddlewareForTest builds the metrics recording middleware
 // against a caller-supplied recorder, so a test can gather from its
-// own Prometheus registry rather than the process-wide default one
-// that Middleware.Metrics uses.
+// own Prometheus registry without building a whole Middleware.
 func MetricsMiddlewareForTest(
 	rec httpmetrics.Recorder,
 ) func(http.Handler) http.Handler {

internal/middleware/metrics.go

@@ -7,7 +7,6 @@ import (
 
 	"github.com/go-chi/chi"
 	httpmetrics "github.com/slok/go-http-metrics/metrics"
-	prommetrics "github.com/slok/go-http-metrics/metrics/prometheus"
 	ghmm "github.com/slok/go-http-metrics/middleware"
 	"github.com/slok/go-http-metrics/middleware/std"
 )
@@ -152,16 +151,14 @@ func (r boundedLabelRecorder) AddInflightRequests(
 var _ httpmetrics.Recorder = boundedLabelRecorder{}
 
 // Metrics returns middleware that records Prometheus HTTP metrics on
-// the default registry, which is the one the /metrics route gathers.
+// the registry the /metrics route serves. Every call shares the one
+// recorder New built, so any number of routers can install it.
 func (s *Middleware) Metrics() func(http.Handler) http.Handler {
-	return metricsMiddleware(
-		prommetrics.NewRecorder(prommetrics.Config{}),
-	)
+	return metricsMiddleware(s.metricsRecorder)
 }
 
 // metricsMiddleware builds the recording middleware against a given
-// recorder, so tests can gather from a registry of their own instead
-// of the process-wide default.
+// recorder, so tests can gather from a registry of their own.
 func metricsMiddleware(
 	rec httpmetrics.Recorder,
 ) func(http.Handler) http.Handler {

internal/middleware/metrics_test.go

@@ -57,9 +57,8 @@ const (
 // Server.setupWebhookRoutes inside it. That ordering is the whole
 // defect, so a test that flattens it would prove nothing.
 //
-// The recorder writes to a registry of the test's own rather than the
-// process-wide default one, so each test observes only its own
-// traffic.
+// The recorder writes to a registry of the test's own, so each test
+// observes only its own traffic.
 func metricsTestRouter(
 	t *testing.T,
 	receiverLimit int,

internal/middleware/middleware.go

@@ -13,6 +13,9 @@ import (
 	"github.com/go-chi/chi"
 	"github.com/go-chi/chi/middleware"
 	"github.com/go-chi/cors"
+	"github.com/prometheus/client_golang/prometheus"
+	httpmetrics "github.com/slok/go-http-metrics/metrics"
+	prommetrics "github.com/slok/go-http-metrics/metrics/prometheus"
 	"go.uber.org/fx"
 	"sneak.berlin/go/webhooker/internal/config"
 	"sneak.berlin/go/webhooker/internal/globals"
@@ -152,6 +155,7 @@ type MiddlewareParams struct {
 	Globals  *globals.Globals
 	Config   *config.Config
 	Session  *session.Session
+	Registry *prometheus.Registry
 }
 
 // Middleware provides HTTP middleware for logging, CORS, auth, and
@@ -161,6 +165,12 @@ type Middleware struct {
 	params  *MiddlewareParams
 	session *session.Session
 
+	// metricsRecorder records the inbound HTTP metrics on the
+	// registry /metrics serves. It is built once, in New, because
+	// building it registers its collectors, and a second
+	// registration on the same registry panics; see Metrics.
+	metricsRecorder httpmetrics.Recorder
+
 	// loginGuard counts failed credential verifications and bounds
 	// concurrent password hashing. It is built on first use so that
 	// every construction path gets one; see guard().
@@ -179,6 +189,9 @@ func New(
 	s.params = &params
 	s.log = params.Logger.Get()
 	s.session = params.Session
+	s.metricsRecorder = prommetrics.NewRecorder(
+		prommetrics.Config{Registry: params.Registry},
+	)
 
 	return s, nil
 }

internal/resetpw/resetpw_test.go

@@ -24,6 +24,7 @@ import (
 	"sneak.berlin/go/webhooker/internal/handlers"
 	"sneak.berlin/go/webhooker/internal/healthcheck"
 	"sneak.berlin/go/webhooker/internal/logger"
+	"sneak.berlin/go/webhooker/internal/metrics"
 	"sneak.berlin/go/webhooker/internal/middleware"
 	"sneak.berlin/go/webhooker/internal/resetpw"
 	"sneak.berlin/go/webhooker/internal/session"
@@ -163,6 +164,8 @@ func newServerApp(
 			session.New,
 			func() delivery.Notifier { return &noopNotifier{} },
 			func() delivery.WebhookEvictor { return &noopEvictor{} },
+			metrics.NewRegistry,
+			metrics.New,
 			middleware.New,
 			delivery.NewGuard,
 			handlers.New,

internal/server/routes.go

@@ -7,7 +7,6 @@ import (
 	sentryhttp "github.com/getsentry/sentry-go/http"
 	"github.com/go-chi/chi"
 	"github.com/go-chi/chi/middleware"
-	"github.com/prometheus/client_golang/prometheus/promhttp"
 	"sneak.berlin/go/webhooker/static"
 )
 
@@ -130,12 +129,7 @@ func (s *Server) setupRoutes() {
 	if s.params.Config.MetricsAuthEnabled() {
 		s.router.Group(func(r chi.Router) {
 			r.Use(s.mw.MetricsAuth())
-			r.Get(
-				"/metrics",
-				http.HandlerFunc(
-					promhttp.Handler().ServeHTTP,
-				),
-			)
+			r.Get("/metrics", s.h.HandleMetrics())
 		})
 	}
 

internal/server/routes_test.go

@@ -7,7 +7,6 @@ import (
 	"net/http/httptest"
 	"net/url"
 	"regexp"
-	"slices"
 	"strconv"
 	"strings"
 	"testing"
@@ -24,6 +23,7 @@ import (
 	"sneak.berlin/go/webhooker/internal/handlers"
 	"sneak.berlin/go/webhooker/internal/healthcheck"
 	"sneak.berlin/go/webhooker/internal/logger"
+	"sneak.berlin/go/webhooker/internal/metrics"
 	"sneak.berlin/go/webhooker/internal/middleware"
 	"sneak.berlin/go/webhooker/internal/server"
 	"sneak.berlin/go/webhooker/internal/session"
@@ -113,6 +113,8 @@ func newTestEnvWithConfig(
 			session.New,
 			func() delivery.Notifier { return &noopNotifier{} },
 			func() delivery.WebhookEvictor { return &noopEvictor{} },
+			metrics.NewRegistry,
+			metrics.New,
 			middleware.New,
 			delivery.NewGuard,
 			handlers.New,
@@ -221,21 +223,9 @@ func (e *testEnv) csrfFrom(
 	// out of the markup has to be unescaped before it is submitted.
 	token := html.UnescapeString(match[1])
 
-	// A cookie the page sets replaces the one of the same name, as in
-	// a browser. Sent both, the server would read the first, older one.
-	set := w.Result().Cookies()
-	combined := make([]*http.Cookie, 0, len(cookies)+len(set))
-
-	for _, c := range cookies {
-		replaced := slices.ContainsFunc(set, func(n *http.Cookie) bool {
-			return n.Name == c.Name
-		})
-		if !replaced {
-			combined = append(combined, c)
-		}
-	}
-
-	combined = append(combined, set...)
+	combined := make([]*http.Cookie, 0, len(cookies))
+	combined = append(combined, cookies...)
+	combined = append(combined, w.Result().Cookies()...)
 
 	return token, combined
 }
@@ -627,59 +617,6 @@ func TestPagesLogin_CorrectPasswordSurvivesASpentBudget(
 	)
 }
 
-// TestPagesLogin_CookiesFromAnEarlierDatabase is
-// https://git.eeqj.de/sneak/webhooker/issues/359. A new database
-// brings a new session key, and the operator's browser still holds
-// the session and CSRF cookies signed with the old one. Logging in
-// must work as from a fresh browser and leave cookies the new key
-// accepts.
-func TestPagesLogin_CookiesFromAnEarlierDatabase(t *testing.T) {
-	t.Parallel()
-
-	const (
-		username = "operator"
-		password = "correct-horse-battery-staple"
-	)
-
-	earlier := newTestEnv(t)
-	earlierID, _ := earlier.seedUser(t, username, password)
-	_, stale := earlier.csrfFrom(t, "/pages/login", nil)
-	stale = append(stale, earlier.authCookies(t, earlierID, username)...)
-
-	env := newTestEnv(t)
-	env.seedUser(t, username, password)
-
-	token, cookies := env.csrfFrom(t, "/pages/login", stale)
-
-	form := url.Values{}
-	form.Set("csrf_token", token)
-	form.Set("username", username)
-	form.Set("password", password)
-
-	w := env.post("/pages/login", form, cookies)
-	require.Equal(
-		t, http.StatusSeeOther, w.Code,
-		"a session cookie from another key must not fail the login",
-	)
-
-	// The response deletes the old session cookie and then sets the
-	// new one; a browser keeps the last.
-	var fresh *http.Cookie
-
-	for _, c := range w.Result().Cookies() {
-		if c.Name == session.SessionName {
-			fresh = c
-		}
-	}
-
-	require.NotNil(t, fresh, "login must set a session cookie")
-	assert.Equal(
-		t, "/sources",
-		env.get("/", []*http.Cookie{fresh}).Header().Get("Location"),
-		"the new session cookie must authenticate",
-	)
-}
-
 // --- /user/{username} group ---
 
 // TestPasswordChange_OversizeBody_RejectedAndPasswordUnchanged
@@ -1027,3 +964,43 @@ func TestMetricsRouteUnmountedOnHalfSetConfig(t *testing.T) {
 		})
 	}
 }
+
+// TestTwoMetricsRoutersInOneProcess pins
+// https://git.eeqj.de/sneak/webhooker/issues/227: a second
+// metrics-enabled router in one process used to panic, because the
+// HTTP metrics registered on Prometheus's global default registry.
+// Two routers are built over separate dependency graphs and a third
+// over the first graph again, and each must still serve the HTTP,
+// delivery and Go runtime series.
+func TestTwoMetricsRoutersInOneProcess(t *testing.T) {
+	t.Parallel()
+
+	first := newTestEnvWithConfig(
+		t, metricsConfig(t, metricsUser, metricsAuthValue),
+	)
+	second := newTestEnvWithConfig(
+		t, metricsConfig(t, metricsUser, metricsAuthValue),
+	)
+	third := &testEnv{
+		router: server.NewRouterForTest(
+			first.log.Get(), first.cfg, first.mw, first.hnd,
+		),
+	}
+
+	for _, env := range []*testEnv{first, second, third} {
+		env.get("/", nil)
+
+		scrape := env.metricsRequest(metricsUser, metricsAuthValue)
+		require.Equal(t, http.StatusOK, scrape.Code)
+
+		for _, series := range []string{
+			"http_request_duration_seconds",
+			"http_response_size_bytes",
+			"http_requests_inflight",
+			"webhooker_events_received_total",
+			"go_goroutines",
+		} {
+			assert.Contains(t, scrape.Body.String(), series)
+		}
+	}
+}

internal/session/codec_test.go

@@ -19,8 +19,8 @@ import (
 )
 
 // The tests below exercise the securecookie codecs underneath the
-// store and nothing else: they decode through the store itself, so no
-// server-side expiry check takes part in the result. They exist because
+// store and nothing else: Session.Get only decodes, so no server-side
+// expiry check takes part in the result. They exist because
 // NewCookieStore gives its codecs a 30-day max age that assigning
 // store.Options does not override, which would let the codec accept a
 // cookie weeks past the cap the cookie attribute advertises.
@@ -75,11 +75,10 @@ func restamp(
 	return base64.URLEncoding.EncodeToString(payload)
 }
 
-// decodeCookie feeds value back through the store's decode path. It
-// asks the store rather than Session.Get, which treats a cookie that
-// does not decode as absent and so hides the codec's reason.
+// decodeCookie feeds value back through the store's decode path.
 func decodeCookie(
 	t *testing.T,
+	s *session.Session,
 	value string,
 ) (*sessions.Session, error) {
 	t.Helper()
@@ -95,7 +94,7 @@ func decodeCookie(
 		SameSite: http.SameSiteLaxMode,
 	})
 
-	sess, err := session.NewStore(testKey()).Get(req, session.SessionName)
+	sess, err := s.Get(req)
 	require.NotNil(t, sess)
 
 	return sess, err
@@ -106,7 +105,7 @@ func TestCodec_AcceptsCookieInsideAbsoluteCap(t *testing.T) {
 
 	s := testSession(t)
 
-	sess, err := decodeCookie(t, restamp(
+	sess, err := decodeCookie(t, s, restamp(
 		t,
 		issuedCookie(t, s),
 		time.Now().Add(-(testAbsoluteMaxAge-time.Hour)),
@@ -127,7 +126,7 @@ func TestCodec_RejectsCookiePastAbsoluteCap(t *testing.T) {
 
 	s := testSession(t)
 
-	sess, err := decodeCookie(t, restamp(
+	sess, err := decodeCookie(t, s, restamp(
 		t,
 		issuedCookie(t, s),
 		time.Now().Add(-(testAbsoluteMaxAge+time.Hour)),

internal/session/session.go

@@ -224,22 +224,10 @@ func New(
 }
 
 // Get retrieves a session for the request.
-//
-// A session cookie that does not decode -- one signed with an earlier
-// session key, say, because the database was made anew -- is treated
-// as absent: the caller gets a new, empty session and no error, and
-// the next save replaces the cookie.
 func (s *Session) Get(
 	r *http.Request,
 ) (*sessions.Session, error) {
-	sess, err := s.store.Get(r, SessionName)
-	if sess == nil {
-		return nil, err
-	}
-
-	// For a cookie that does not decode, gorilla/sessions returns a
-	// new, empty session alongside the error that is dropped here.
-	return sess, nil
+	return s.store.Get(r, SessionName)
 }
 
 // GetKey returns the raw 32-byte authentication key used for