Serve Prometheus metrics at /metrics behind basic auth (closes #94 )

With METRICS_USERNAME and METRICS_PASSWORD both set, the backend records request metrics through go-http-metrics in a registry of its own, with Go's runtime and process metrics, and serves them at GET /metrics behind basic auth with those credentials; nginx passes /metrics to it. With neither set there is no such route; one alone stops the start with an error naming both, and a METRICS_USERNAME containing ":" stops it with an error naming that. Only requests that reach the health check or POST /api/v1/reports are recorded, not every request as the conventions show: the labels are path and method, which clients can make up without end. So POST /api/v1/reports is registered by its full path, not inside a route group. Deviation: go get and go mod tidy ran directly; no entrypoint adds a Go dependency yet (#45). Model: opus-5-5
Shim make dev and make build, format backend/ markdown (closes #28 )
2026-10-04 02:36:10 +00:00 · 2026-10-04 04:14:59 +02:00
21 changed files with 381 additions and 58 deletions
@@ -1,6 +1,7 @@
-backend/
 dist/
 node_modules/
 tmp/
 yarn.lock
 .claude/
+# The org standard file, copied verbatim; backend/script/lint checks its sha256.
+backend/.golangci.yml
@@ -1,6 +1,6 @@
 # The one image netwatch ships: nginx serves the built frontend and
-# passes /api/ and /.well-known/healthcheck to netwatch-server, the Go
-# backend, which runs in the same container on loopback only.
+# passes /api/, /.well-known/healthcheck and /metrics to netwatch-server,
+# the Go backend, which runs in the same container on loopback only.
 # bin/entrypoint.sh starts and watches both.

 # Lint stage — fast feedback on formatting and lint issues. The
@@ -1,5 +1,5 @@
-.PHONY: bootstrap setup dev test lint fmt fmt-check check frontend-check \
-	frontend-viewport-test docker hooks
+.PHONY: bootstrap setup dev build test lint fmt fmt-check check \
+	frontend-check frontend-viewport-test docker hooks

 # Standard targets are thin shims; the implementations live in script/
 # per the scripts-to-rule-them-all pattern (see the Entrypoints section
@@ -13,7 +13,11 @@ setup:
 	@script/setup

 dev:
-	yarn dev
+	@script/dev
+
+# The frontend only; backend/Makefile's build target builds the Go server.
+build:
+	@script/build

 test:
 	@script/test
@@ -46,6 +46,10 @@ halves, so the root `make check` fails if either one is broken. We provide:
  both linters in Docker
 - `script/setup` — make a fresh clone ready for development: bootstrap plus the
  git pre-commit hook
+- `script/dev` — run the Vite dev server, which proxies `/api` to a locally
+  running `netwatch-server`
+- `script/build` — build the frontend for production into `dist/`;
+  `backend/script/build` builds the Go server
 - `script/projectname` — print the project name (used for the Docker image tag)
 - `script/test` — run `script/frontend-test`, then `backend/script/test`, the
  backend's Go tests with the race detector and coverage
@@ -61,7 +65,8 @@ halves, so the root `make check` fails if either one is broken. We provide:
 - `script/frontend-lint` — run eslint with the rules in `eslint.config.js`; it
  runs inside the `frontend-lint` stage of `Dockerfile`, which `make lint`
  builds
- `script/frontend-fmt` — format everything prettier understands (writes)
+- `script/frontend-fmt` — format everything prettier understands (writes), the
+  markdown in `backend/` included
 - `script/frontend-fmt-check` — check prettier formatting (read-only)
 - `script/frontend-check` — run `script/frontend-test` and
  `script/frontend-fmt-check`, for the frontend stage of `Dockerfile`, which has
@@ -196,9 +201,9 @@ static file host (S3, GCS, Cloudflare Pages, Vercel, Netlify, GitHub Pages) or
 use the Docker image behind a reverse proxy.

 The Docker image, built from `Dockerfile`, is the whole service in one
-container: nginx serves the built frontend and passes `/api/` and
-`/.well-known/healthcheck` to the Go backend, `netwatch-server`, which listens
-only inside the container, on `127.0.0.1:8081`. The image:
+container: nginx serves the built frontend and passes `/api/`,
+`/.well-known/healthcheck` and `/metrics` to the Go backend, `netwatch-server`,
+which listens only inside the container, on `127.0.0.1:8081`. The image:

 - Listens on port 8080 by default (override with `PORT` env var)
 - Takes the client address from `X-Forwarded-For` only on requests from the
@@ -246,6 +251,12 @@ What the [upaas](https://git.eeqj.de/sneak/upaas) app for netwatch needs:
      connects from one can write its own `X-Forwarded-For`, and through a port
      Docker publishes, every client may connect from the Docker network's
      gateway, such as `172.17.0.1`.
+    - `METRICS_USERNAME` and `METRICS_PASSWORD`, default empty: with both set,
+      the backend records Prometheus metrics of its requests and serves them at
+      `/metrics` on the container port, to requests with this user name and
+      password as their basic auth credentials. With neither set, there are no
+      metrics and `/metrics` is not found. One set without the other, or a user
+      name containing `:`, stops the container
 - **Health check:** the image's `HEALTHCHECK` requests
  `/.well-known/healthcheck` through nginx every 30 seconds, so it fails unless
  both nginx and the backend answer. upaas reads the container's health 60
@@ -23,6 +23,29 @@ latest run passes.

 # Completed Steps

+- 2026-10-04: the backend serves Prometheus metrics (issue #94). With
+  `METRICS_USERNAME` and `METRICS_PASSWORD` both set, it records request
+  duration and response size through `go-http-metrics` and serves them, with
+  Go's runtime and process metrics, at `GET /metrics` behind basic auth with
+  those credentials; nginx passes `/metrics` to it as it does `/api/`. With
+  neither set there are no metrics and `/metrics` is 404; one without the other
+  stops the start with an error naming both, and so does a `METRICS_USERNAME`
+  containing `:`, with an error naming it. Only requests that reach the health
+  check or `POST /api/v1/reports` are recorded, not `/metrics` itself and not
+  every request as `GO_HTTP_SERVER_CONVENTIONS.md` shows, because the labels are
+  the request's path and method, which clients can make up without end. For
+  that, `POST /api/v1/reports` is now registered by its full path instead of
+  inside a `/api/v1` route group; it answers as before
+- 2026-10-04: `script/` and `Makefile` follow the org models (issue #28):
+  `make dev` shims to the new `script/dev`, the Vite dev server, and the new
+  `make build` to `script/build`, the frontend production build.
+  `.prettierignore` no longer leaves out `backend/`, so `make fmt` and
+  `make fmt-check` cover `backend/README.md`; it leaves out
+  `backend/.golangci.yml` by name, the org standard file whose sha256
+  `backend/script/lint` checks. `script/install-precommit` and the date on
+  `script/bootstrap`'s pins are the org model again; `script/bootstrap`,
+  `script/fmt` and `script/fmt-check` each say in a comment why they differ from
+  it
 - 2026-10-04: a frontend build on Node 26 or newer, such as `make test` on a
  host with Node 26, no longer prints Node's warning that `module.register()` is
  deprecated (issue #32); the build in `Dockerfile` runs on Node 22, which never
@@ -32,17 +32,16 @@ pattern as the repo root: the targets in `backend/Makefile` are thin shims over
 `test`, `fmt` and `fmt-check`:

 - `script/build` — compile the static `netwatch-server` binary with its version
-  stamped in. The version is `VERSION` from the environment;
-  when that is unset or empty, it falls back to `git describe` inside a git
-  checkout, then to `dev`
+  stamped in. The version is `VERSION` from the environment; when that is unset
+  or empty, it falls back to `git describe` inside a git checkout, then to `dev`
 - `script/test` — run the Go tests with the race detector and coverage. Go's
  `-timeout 30s` bounds the tests, not their compile. If they fail, they run
  again with `-v` for the details, and the script fails. The race detector needs
  a C compiler
 - `script/lint` — check `.golangci.yml` against its pinned sha256, then run
-  golangci-lint. It runs inside the golangci-lint image of the lint stage of
-  the root `Dockerfile`; from a checkout, run `make lint` at the repo root,
-  which builds that stage
+  golangci-lint. It runs inside the golangci-lint image of the lint stage of the
+  root `Dockerfile`; from a checkout, run `make lint` at the repo root, which
+  builds that stage
 - `script/fmt` — format the Go sources (writes)
 - `script/fmt-check` — check Go formatting (read-only)
 - `script/run` — build and run the server locally
@@ -61,8 +60,9 @@ flushes them to compressed files on disk for later analysis.

 ## Design

-The server is structured as an `fx`-wired Go application under `cmd/netwatch-server/`.
-Internal packages in `internal/` follow standard Go project layout:
+The server is structured as an `fx`-wired Go application under
+`cmd/netwatch-server/`. Internal packages in `internal/` follow standard Go
+project layout:

 - **`config`**: Loads configuration from environment variables and config files
  via Viper.
@@ -88,12 +88,15 @@ Internal packages in `internal/` follow standard Go project layout:
 | `TRUSTED_PROXIES`      | loopback + RFC1918   | Comma-separated CIDRs whose `X-Forwarded-For` / `X-Real-IP` headers are trusted for client IP resolution |
 | `REPORTS_PER_MINUTE`   | `60`                 | Reports each client address may send a minute; see [Report limits](#report-limits)                       |
 | `CORS_ALLOWED_ORIGINS` | empty                | Comma-separated origins whose pages may call the API; see [CORS](#cors)                                  |
+| `METRICS_USERNAME`     | empty                | Basic auth user name for `/metrics`; see [Metrics](#metrics)                                             |
+| `METRICS_PASSWORD`     | empty                | Basic auth password for `/metrics`; see [Metrics](#metrics)                                              |

-`TRUSTED_PROXIES` defaults to `127.0.0.1/32,::1/128,10.0.0.0/8,172.16.0.0/12,192.168.0.0/16`.
-The loopback entries cover a reverse proxy on the same host. A request whose
-direct peer is outside this set has its forwarded headers ignored, and the
-direct peer is logged and rate-limited instead. The container image does not use
-this default; see [Container image](#container-image).
+`TRUSTED_PROXIES` defaults to
+`127.0.0.1/32,::1/128,10.0.0.0/8,172.16.0.0/12,192.168.0.0/16`. The loopback
+entries cover a reverse proxy on the same host. A request whose direct peer is
+outside this set has its forwarded headers ignored, and the direct peer is
+logged and rate-limited instead. The container image does not use this default;
+see [Container image](#container-image).

 A variable set to a value the server cannot use, such as `PORT=abc`,
 `DEBUG=maybe` or a `BIND_ADDRESS` that is not an IP address, stops it from
@@ -102,16 +105,16 @@ starting, with an error naming the variable. An empty variable counts as unset.
 ### Container image

 The root `Dockerfile` builds one image in which nginx listens on the public port
-8080, serves the frontend, and proxies `/api/` and `/.well-known/healthcheck` to
-this server. The image's entrypoint, `bin/entrypoint.sh`, starts the server as
-user `netwatch` (uid 1000) with `BIND_ADDRESS=127.0.0.1` and `PORT=8081`, so
-only nginx reaches it, and with `TRUSTED_PROXIES=127.0.0.1/32`, so it takes the
-client address nginx passes on and no other. `DATA_DIR` is `/data/reports`, on
-the `/data` volume; before starting the server, the entrypoint creates it and
-gives it and `/data` to `netwatch` with `netwatch-server prepare-data-dir`,
-which acts on nothing outside `/data`. nginx replaces the security headers
-this server sets with those in the root `security-headers.conf`, so those are
-what clients of the image see.
+8080, serves the frontend, and proxies `/api/`, `/.well-known/healthcheck` and
+`/metrics` to this server. The image's entrypoint, `bin/entrypoint.sh`, starts
+the server as user `netwatch` (uid 1000) with `BIND_ADDRESS=127.0.0.1` and
+`PORT=8081`, so only nginx reaches it, and with `TRUSTED_PROXIES=127.0.0.1/32`,
+so it takes the client address nginx passes on and no other. `DATA_DIR` is
+`/data/reports`, on the `/data` volume; before starting the server, the
+entrypoint creates it and gives it and `/data` to `netwatch` with
+`netwatch-server prepare-data-dir`, which acts on nothing outside `/data`. nginx
+replaces the security headers this server sets with those in the root
+`security-headers.conf`, so those are what clients of the image see.

 The container's own `TRUSTED_PROXIES` goes to nginx instead: IP addresses or
 CIDRs, separated by commas, of the reverse proxies in front of the container.
@@ -162,8 +165,7 @@ credentials, so it is bounded instead. Both refusals below answer with the same
  to be written fill the cap on their own, and then no file is deleted. At
  start, report files past the cap, as after lowering it, are deleted the same
  way. So the cap is how much of the newest reports is kept: the default of 1
-  GiB is small enough for any host; set it to the space you can give
-  `DATA_DIR`.
+  GiB is small enough for any host; set it to the space you can give `DATA_DIR`.

 ### CORS

@@ -176,6 +178,26 @@ origin, `scheme://host` with an optional `:port`, as browsers send it: no path,
 not even a trailing `/`, and no `*`. Any other entry stops the server from
 starting, with an error naming `CORS_ALLOWED_ORIGINS`.

+### Metrics
+
+With both `METRICS_USERNAME` and `METRICS_PASSWORD` set, the server serves
+Prometheus metrics at `GET /metrics` to requests with those as their basic auth
+credentials, and answers any other with 401. For each request that reaches the
+health check or `POST /api/v1/reports`, those the rate limit refuses included,
+the metrics record its duration and response size, labelled with its path,
+method and status; they also count those requests in progress, and include Go's
+runtime and process metrics. No other request is recorded: not those to
+`/metrics` itself, and not those answered before they reach either route, such
+as a CORS preflight, or a request refused with 404 for a path no route has, 405
+for a method its route does not take, or 413 for declaring a body length over
+the 1 MiB limit. A report whose body goes over the limit without declaring its
+length reaches the route, is answered 413 there, and is recorded with that
+status. Clients can make up any number of paths and methods, and each would add
+labels to the metrics for as long as the server runs. With neither set, nothing
+is recorded and `/metrics` answers 404. One without the other stops the server
+from starting, with an error naming both; so does a `METRICS_USERNAME`
+containing `:`, which basic auth cannot carry, with an error naming it.
+
 ## TODO

 - Add integration test that POSTs a report and verifies the compressed output
@@ -3,20 +3,29 @@ module sneak.berlin/go/netwatch
 go 1.25.5

 require (
+	github.com/99designs/basicauth-go v0.0.0-20230316000542-bf6f9cbbf0f8
 	github.com/go-chi/chi/v5 v5.2.5
 	github.com/go-chi/cors v1.2.2
 	github.com/go-chi/httprate v0.16.0
 	github.com/joho/godotenv v1.5.1
-	github.com/klauspost/compress v1.18.4
+	github.com/klauspost/compress v1.19.1
+	github.com/prometheus/client_golang v1.24.1
+	github.com/slok/go-http-metrics v0.13.0
 	github.com/spf13/viper v1.21.0
 	go.uber.org/fx v1.24.0
 )

 require (
+	github.com/beorn7/perks v1.0.1 // indirect
+	github.com/cespare/xxhash/v2 v2.3.0 // indirect
 	github.com/fsnotify/fsnotify v1.9.0 // indirect
 	github.com/go-viper/mapstructure/v2 v2.4.0 // indirect
 	github.com/klauspost/cpuid/v2 v2.2.10 // indirect
+	github.com/munnerz/goautoneg v0.0.0-20191010083416-a7dc8b61c822 // indirect
 	github.com/pelletier/go-toml/v2 v2.2.4 // indirect
+	github.com/prometheus/client_model v0.6.2 // indirect
+	github.com/prometheus/common v0.70.1 // indirect
+	github.com/prometheus/procfs v0.21.1 // indirect
 	github.com/sagikazarmark/locafero v0.11.0 // indirect
 	github.com/sourcegraph/conc v0.3.1-0.20240121214520-5f936abd7ae8 // indirect
 	github.com/spf13/afero v1.15.0 // indirect
@@ -28,6 +37,7 @@ require (
 	go.uber.org/multierr v1.10.0 // indirect
 	go.uber.org/zap v1.26.0 // indirect
 	go.yaml.in/yaml/v3 v3.0.4 // indirect
-	golang.org/x/sys v0.30.0 // indirect
-	golang.org/x/text v0.28.0 // indirect
+	golang.org/x/sys v0.47.0 // indirect
+	golang.org/x/text v0.40.0 // indirect
+	google.golang.org/protobuf v1.36.11 // indirect
 )
@@ -1,3 +1,9 @@
+github.com/99designs/basicauth-go v0.0.0-20230316000542-bf6f9cbbf0f8 h1:nMpu1t4amK3vJWBibQ5X/Nv0aXL+b69TQf2uK5PH7Go=
+github.com/99designs/basicauth-go v0.0.0-20230316000542-bf6f9cbbf0f8/go.mod h1:3cARGAK9CfW3HoxCy1a0G4TKrdiKke8ftOMEOHyySYs=
+github.com/beorn7/perks v1.0.1 h1:VlbKKnNfV8bJzeqoa4cOKqO6bYr3WgKZxO8Z16+hsOM=
+github.com/beorn7/perks v1.0.1/go.mod h1:G2ZrVWU2WbWT9wwq4/hrbKbnv/1ERSJQ0ibhJ6rlkpw=
+github.com/cespare/xxhash/v2 v2.3.0 h1:UL815xU9SqsFlibzuggzjXhog7bL6oX9BbNZnL2UFvs=
+github.com/cespare/xxhash/v2 v2.3.0/go.mod h1:VGX0DQ3Q6kWi7AoAeZDth3/j3BFtOZR5XLFGgcrjCOs=
 github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c=
 github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
 github.com/frankban/quicktest v1.14.6 h1:7Xjx+VpznH+oBnejlPUj8oUpdxnVs4f8XU8WnHkI4W8=
@@ -12,26 +18,40 @@ github.com/go-chi/httprate v0.16.0 h1:8V5DH9j6pSK6UQoBsTpvMyFxycqaKEIToyPKzHJjUa
 github.com/go-chi/httprate v0.16.0/go.mod h1:A8lo+qRhk+s9LiuP5saS7XCGDXRXMcrueq0NfIuCa/I=
 github.com/go-viper/mapstructure/v2 v2.4.0 h1:EBsztssimR/CONLSZZ04E8qAkxNYq4Qp9LvH92wZUgs=
 github.com/go-viper/mapstructure/v2 v2.4.0/go.mod h1:oJDH3BJKyqBA2TXFhDsKDGDTlndYOZ6rGS0BRZIxGhM=
-github.com/google/go-cmp v0.6.0 h1:ofyhxvXcZhMsU5ulbFiLKl/XBFqE1GSq7atu8tAmTRI=
-github.com/google/go-cmp v0.6.0/go.mod h1:17dUlkBOakJ0+DkrSSNjCkIjxS6bF9zb3elmeNGIjoY=
+github.com/google/go-cmp v0.7.0 h1:wk8382ETsv4JYUZwIsn6YpYiWiBsYLSJiTsyBybVuN8=
+github.com/google/go-cmp v0.7.0/go.mod h1:pXiqmnSA92OHEEa9HXL2W4E7lf9JzCmGVUdgjX3N/iU=
 github.com/joho/godotenv v1.5.1 h1:7eLL/+HRGLY0ldzfGMeQkb7vMd0as4CfYvUVzLqw0N0=
 github.com/joho/godotenv v1.5.1/go.mod h1:f4LDr5Voq0i2e/R5DDNOoa2zzDfwtkZa6DnEwAbqwq4=
-github.com/klauspost/compress v1.18.4 h1:RPhnKRAQ4Fh8zU2FY/6ZFDwTVTxgJ/EMydqSTzE9a2c=
-github.com/klauspost/compress v1.18.4/go.mod h1:R0h/fSBs8DE4ENlcrlib3PsXS61voFxhIs2DeRhCvJ4=
+github.com/klauspost/compress v1.19.1 h1:VsB4HPswih7mmZ8WleSFQ75c/Ui1M4trX5oAsJnhSlk=
+github.com/klauspost/compress v1.19.1/go.mod h1:cwPg85FWrGar70rWktvGQj8/hthj3wpl0PGDogxkrSQ=
 github.com/klauspost/cpuid/v2 v2.2.10 h1:tBs3QSyvjDyFTq3uoc/9xFpCuOsJQFNPiAhYdw2skhE=
 github.com/klauspost/cpuid/v2 v2.2.10/go.mod h1:hqwkgyIinND0mEev00jJYCxPNVRVXFQeu1XKlok6oO0=
 github.com/kr/pretty v0.3.1 h1:flRD4NNwYAUpkphVc1HcthR4KEIFJ65n8Mw5qdRn3LE=
 github.com/kr/pretty v0.3.1/go.mod h1:hoEshYVHaxMs3cyo3Yncou5ZscifuDolrwPKZanG3xk=
 github.com/kr/text v0.2.0 h1:5Nx0Ya0ZqY2ygV366QzturHI13Jq95ApcVaJBhpS+AY=
 github.com/kr/text v0.2.0/go.mod h1:eLer722TekiGuMkidMxC/pM04lWEeraHUUmBw8l2grE=
+github.com/kylelemons/godebug v1.1.0 h1:RPNrshWIDI6G2gRW9EHilWtl7Z6Sb1BR0xunSBf0SNc=
+github.com/kylelemons/godebug v1.1.0/go.mod h1:9/0rRGxNHcop5bhtWyNeEfOS8JIWk580+fNqagV/RAw=
+github.com/munnerz/goautoneg v0.0.0-20191010083416-a7dc8b61c822 h1:C3w9PqII01/Oq1c1nUAm88MOHcQC9l5mIlSMApZMrHA=
+github.com/munnerz/goautoneg v0.0.0-20191010083416-a7dc8b61c822/go.mod h1:+n7T8mK8HuQTcFwEeznm/DIxMOiR9yIdICNftLE1DvQ=
 github.com/pelletier/go-toml/v2 v2.2.4 h1:mye9XuhQ6gvn5h28+VilKrrPoQVanw5PMw/TB0t5Ec4=
 github.com/pelletier/go-toml/v2 v2.2.4/go.mod h1:2gIqNv+qfxSVS7cM2xJQKtLSTLUE9V8t9Stt+h56mCY=
 github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZbAQM=
 github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
+github.com/prometheus/client_golang v1.24.1 h1:JnJkREXzWxUdCuPFpIWZiPispT9xVV59uiuyR2bPlnU=
+github.com/prometheus/client_golang v1.24.1/go.mod h1:F+oSRECHg4sse5ucfYpYDeIv/hu68Zo0uoHKetWnzcE=
+github.com/prometheus/client_model v0.6.2 h1:oBsgwpGs7iVziMvrGhE53c/GrLUsZdHnqNwqPLxwZyk=
+github.com/prometheus/client_model v0.6.2/go.mod h1:y3m2F6Gdpfy6Ut/GBsUqTWZqCUvMVzSfMLjcu6wAwpE=
+github.com/prometheus/common v0.70.1 h1:1HvjP4D5oL3t8RsPlwxA9onvvStjtIHYE5XuuwOi/PY=
+github.com/prometheus/common v0.70.1/go.mod h1:VdFUQDMZK3VLkurFUVhia6uys/0suUp86TJz5qbJRhc=
+github.com/prometheus/procfs v0.21.1 h1:GljZCt+zSTS+NZq88cyQ1LjZ+RCHp3uVuabBWA5+OJI=
+github.com/prometheus/procfs v0.21.1/go.mod h1:aB55Cww9pdSJVHk0hUf0inxWyyjPogFIjmHKYgMKmtY=
 github.com/rogpeppe/go-internal v1.9.0 h1:73kH8U+JUqXU8lRuOHeVHaa/SZPifC7BkcraZVejAe8=
 github.com/rogpeppe/go-internal v1.9.0/go.mod h1:WtVeX8xhTBvf0smdhujwtBcq4Qrzq/fJaraNFVN+nFs=
 github.com/sagikazarmark/locafero v0.11.0 h1:1iurJgmM9G3PA/I+wWYIOw/5SyBtxapeHDcg+AAIFXc=
 github.com/sagikazarmark/locafero v0.11.0/go.mod h1:nVIGvgyzw595SUSUE6tvCp3YYTeHs15MvlmU87WwIik=
+github.com/slok/go-http-metrics v0.13.0 h1:lQDyJJx9wKhmbliyUsZ2l6peGnXRHjsjoqPt5VYzcP8=
+github.com/slok/go-http-metrics v0.13.0/go.mod h1:HIr7t/HbN2sJaunvnt9wKP9xoBBVZFo1/KiHU3b0w+4=
 github.com/sourcegraph/conc v0.3.1-0.20240121214520-5f936abd7ae8 h1:+jumHNA0Wrelhe64i8F6HNlS8pkoyMv5sreGx2Ry5Rw=
 github.com/sourcegraph/conc v0.3.1-0.20240121214520-5f936abd7ae8/go.mod h1:3n1Cwaq1E1/1lhQhtRK2ts/ZwZEhjcQeJQ1RuC6Q/8U=
 github.com/spf13/afero v1.15.0 h1:b/YBCLWAJdFWJTN9cLhiXXcD7mzKn9Dm86dNnfyQw1I=
@@ -42,6 +62,8 @@ github.com/spf13/pflag v1.0.10 h1:4EBh2KAYBwaONj6b2Ye1GiHfwjqyROoF4RwYO+vPwFk=
 github.com/spf13/pflag v1.0.10/go.mod h1:McXfInJRrz4CZXVZOBLb0bTZqETkiAhM9Iw0y3An2Bg=
 github.com/spf13/viper v1.21.0 h1:x5S+0EU27Lbphp4UKm1C+1oQO+rKx36vfCoaVebLFSU=
 github.com/spf13/viper v1.21.0/go.mod h1:P0lhsswPGWD/1lZJ9ny3fYnVqxiegrlNrEmgLjbTCAY=
+github.com/stretchr/objx v0.5.2 h1:xuMeJ0Sdp5ZMRXx/aWO6RZxdr3beISkG5/G/aIRr3pY=
+github.com/stretchr/objx v0.5.2/go.mod h1:FRsXN1f5AsAjCGJKqEizvkpNtU+EGNCLh3NxZ/8L+MA=
 github.com/stretchr/testify v1.11.1 h1:7s2iGBzp5EwR7/aIZr8ao5+dra3wiQyKjjFuvgVKu7U=
 github.com/stretchr/testify v1.11.1/go.mod h1:wZwfW3scLgRK+23gO65QZefKpKQRnfz6sD981Nm4B6U=
 github.com/subosito/gotenv v1.6.0 h1:9NlTDc1FTs4qu0DDq7AEtTPNw6SVm7uBMsUCUjABIf8=
@@ -54,18 +76,22 @@ go.uber.org/dig v1.19.0 h1:BACLhebsYdpQ7IROQ1AGPjrXcP5dF80U3gKoFzbaq/4=
 go.uber.org/dig v1.19.0/go.mod h1:Us0rSJiThwCv2GteUN0Q7OKvU7n5J4dxZ9JKUXozFdE=
 go.uber.org/fx v1.24.0 h1:wE8mruvpg2kiiL1Vqd0CC+tr0/24XIB10Iwp2lLWzkg=
 go.uber.org/fx v1.24.0/go.mod h1:AmDeGyS+ZARGKM4tlH4FY2Jr63VjbEDJHtqXTGP5hbo=
-go.uber.org/goleak v1.2.0 h1:xqgm/S+aQvhWFTtR0XK3Jvg7z8kGV8P4X14IzwN3Eqk=
-go.uber.org/goleak v1.2.0/go.mod h1:XJYK+MuIchqpmGmUSAzotztawfKvYLUIgg7guXrwVUo=
+go.uber.org/goleak v1.3.0 h1:2K3zAYmnTNqV73imy9J1T3WC+gmCePx2hEGkimedGto=
+go.uber.org/goleak v1.3.0/go.mod h1:CoHD4mav9JJNrW/WLlf7HGZPjdw8EucARQHekz1X6bE=
 go.uber.org/multierr v1.10.0 h1:S0h4aNzvfcFsC3dRF1jLoaov7oRaKqRGC/pUEJ2yvPQ=
 go.uber.org/multierr v1.10.0/go.mod h1:20+QtiLqy0Nd6FdQB9TLXag12DsQkrbs3htMFfDN80Y=
 go.uber.org/zap v1.26.0 h1:sI7k6L95XOKS281NhVKOFCUNIvv9e0w4BF8N3u+tCRo=
 go.uber.org/zap v1.26.0/go.mod h1:dtElttAiwGvoJ/vj4IwHBS/gXsEu/pZ50mUIRWuG0so=
+go.yaml.in/yaml/v2 v2.4.4 h1:tuyd0P+2Ont/d6e2rl3be67goVK4R6deVxCUX5vyPaQ=
+go.yaml.in/yaml/v2 v2.4.4/go.mod h1:gMZqIpDtDqOfM0uNfy0SkpRhvUryYH0Z6wdMYcacYXQ=
 go.yaml.in/yaml/v3 v3.0.4 h1:tfq32ie2Jv2UxXFdLJdh3jXuOzWiL1fo0bu/FbuKpbc=
 go.yaml.in/yaml/v3 v3.0.4/go.mod h1:DhzuOOF2ATzADvBadXxruRBLzYTpT36CKvDb3+aBEFg=
-golang.org/x/sys v0.30.0 h1:QjkSwP/36a20jFYWkSue1YwXzLmsV5Gfq7Eiy72C1uc=
-golang.org/x/sys v0.30.0/go.mod h1:/VUhepiaJMQUp4+oa/7Zr1D23ma6VTLIYjOOTFZPUcA=
-golang.org/x/text v0.28.0 h1:rhazDwis8INMIwQ4tpjLDzUhx6RlXqZNPEM0huQojng=
-golang.org/x/text v0.28.0/go.mod h1:U8nCwOR8jO/marOQ0QbDiOngZVEBB7MAiitBuMjXiNU=
+golang.org/x/sys v0.47.0 h1:o7XGOvZQCADBQQ4Y7VNq2dRWQR7JmOUW8Kxx4ZsNgWs=
+golang.org/x/sys v0.47.0/go.mod h1:4GL1E5IUh+htKOUEOaiffhrAeqysfVGipDYzABqnCmw=
+golang.org/x/text v0.40.0 h1:Ub2Z6/xjgF1WrYQz2nuITOEegKFtiIy+rieRJ5lHZKs=
+golang.org/x/text v0.40.0/go.mod h1:hpnzDAfGV753zIKo+wk3u1bVKCGPbrnF7+7LBF/UHVY=
+google.golang.org/protobuf v1.36.11 h1:fV6ZwhNocDyBLK0dj+fg8ektcVegBBuEolpbTQyBNVE=
+google.golang.org/protobuf v1.36.11/go.mod h1:HTf+CrKn2C3g5S8VImy6tdcUvCska2kB7j23XfzDpco=
 gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
 gopkg.in/check.v1 v1.0.0-20190902080502-41f04d3bba15 h1:YR8cESwS4TdDjEe65xsg0ogRM/Nc3DYOhEAlW+xobZo=
 gopkg.in/check.v1 v1.0.0-20190902080502-41f04d3bba15/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
@@ -44,6 +44,15 @@ var (
 	errNotPort = errors.New("must be a port number, 1 to 65535")
 	errNotBool = errors.New("must be true or false")
 	errNotIP   = errors.New("must be an IP address, or empty")
+
+	errMetricsCredentials = errors.New(
+		"METRICS_USERNAME and METRICS_PASSWORD must be set together, " +
+			"or neither",
+	)
+	errMetricsUsernameColon = errors.New(
+		"METRICS_USERNAME must not contain \":\", " +
+			"which basic auth cannot carry in a user name",
+	)
 )

 // Params defines the dependencies for Config.
@@ -178,6 +187,18 @@ func (s *Config) check() error {
 		}
 	}

+	// The server records and serves metrics only with both set, so
+	// one alone is a mistake that would otherwise go unnoticed.
+	if (s.MetricsUsername == "") != (s.MetricsPassword == "") {
+		return errMetricsCredentials
+	}
+
+	// Basic auth splits the credentials at the first ":", so with one
+	// in the user name every request to /metrics would get 401.
+	if strings.Contains(s.MetricsUsername, ":") {
+		return errMetricsUsernameColon
+	}
+
 	return checkOrigins(s.CORSAllowedOrigins)
 }

@@ -103,6 +103,32 @@ func TestDataDirMaxBytesMustBeANumber(t *testing.T) {
 	requireConfigError(t, "DATA_DIR_MAX_BYTES")
 }

+// TestMetricsCredentialsGoTogether: with only one of the two set, the
+// server would quietly serve no metrics, so the start fails, naming
+// both.
+func TestMetricsCredentialsGoTogether(t *testing.T) {
+	for _, set := range []string{"METRICS_USERNAME", "METRICS_PASSWORD"} {
+		t.Run(set, func(t *testing.T) {
+			t.Setenv("METRICS_USERNAME", "")
+			t.Setenv("METRICS_PASSWORD", "")
+			t.Setenv(set, "prometheus")
+
+			requireConfigError(t, "METRICS_USERNAME")
+			requireConfigError(t, "METRICS_PASSWORD")
+		})
+	}
+}
+
+// TestMetricsUsernameMustNotContainColon: basic auth splits the
+// credentials at the first ":", so such a user name would get 401 on
+// every request to /metrics.
+func TestMetricsUsernameMustNotContainColon(t *testing.T) {
+	t.Setenv("METRICS_USERNAME", "prom:etheus")
+	t.Setenv("METRICS_PASSWORD", "secret")
+
+	requireConfigError(t, "METRICS_USERNAME")
+}
+
 // TestCORSAllowedOriginsMustBeOrigins: "*" would let every origin in,
 // and an entry that is not a plain origin would match no page.
 func TestCORSAllowedOriginsMustBeOrigins(t *testing.T) {
@@ -18,9 +18,14 @@ import (
 	"sneak.berlin/go/netwatch/internal/globals"
 	"sneak.berlin/go/netwatch/internal/logger"

+	basicauth "github.com/99designs/basicauth-go"
 	"github.com/go-chi/chi/v5/middleware"
 	"github.com/go-chi/cors"
 	"github.com/go-chi/httprate"
+	"github.com/prometheus/client_golang/prometheus"
+	metrics "github.com/slok/go-http-metrics/metrics/prometheus"
+	ghmm "github.com/slok/go-http-metrics/middleware"
+	"github.com/slok/go-http-metrics/middleware/std"
 	"go.uber.org/fx"
 )

@@ -364,3 +369,25 @@ func (s *Middleware) RateLimit(
 		),
 	)
 }
+
+// Metrics returns middleware that records each request's duration and
+// response size, and the requests in progress, in registry. They are
+// labelled by the request path.
+func (s *Middleware) Metrics(
+	registry prometheus.Registerer,
+) func(http.Handler) http.Handler {
+	mdlw := ghmm.New(ghmm.Config{
+		Recorder: metrics.NewRecorder(metrics.Config{Registry: registry}),
+	})
+
+	return std.HandlerProvider("", mdlw)
+}
+
+// MetricsAuth returns middleware that lets a request through only with
+// METRICS_USERNAME and METRICS_PASSWORD as its basic auth credentials,
+// and answers any other with 401.
+func (s *Middleware) MetricsAuth() func(http.Handler) http.Handler {
+	return basicauth.New("metrics", map[string][]string{
+		s.params.Config.MetricsUsername: {s.params.Config.MetricsPassword},
+	})
+}
@@ -5,6 +5,9 @@ import (

 	"github.com/go-chi/chi/v5"
 	"github.com/go-chi/chi/v5/middleware"
+	"github.com/prometheus/client_golang/prometheus"
+	"github.com/prometheus/client_golang/prometheus/collectors"
+	"github.com/prometheus/client_golang/prometheus/promhttp"
 )

 const (
@@ -29,13 +32,37 @@ func (s *Server) SetupRoutes() {
 	s.router.Use(s.mw.MaxBodyBytes(maxRequestBodyBytes))
 	s.router.Use(middleware.Timeout(requestTimeout))

-	s.router.Get(
-		"/.well-known/healthcheck",
-		s.h.HandleHealthCheck(),
+	// The metrics go in a registry of this server's own, not in
+	// Prometheus' default one, which takes them only once per process.
+	registry := prometheus.NewRegistry()
+	registry.MustRegister(
+		collectors.NewGoCollector(),
+		collectors.NewProcessCollector(collectors.ProcessCollectorOpts{}),
 	)

-	s.router.Route("/api/v1", func(r chi.Router) {
+	// Requests are measured only once chi has matched them to one of
+	// these routes, by path and method. The metrics are labelled with
+	// both, which any client can make up, so measuring every request
+	// would let clients add labels without bound. A Route here would
+	// be matched by its path prefix alone, so each path is given in
+	// full.
+	s.router.Group(func(r chi.Router) {
+		// config.New refuses one of the two credentials without the
+		// other.
+		if s.params.Config.MetricsUsername != "" {
+			r.Use(s.mw.Metrics(registry))
+		}
+
+		r.Get("/.well-known/healthcheck", s.h.HandleHealthCheck())
+
 		r.With(s.mw.RateLimit(s.params.Config.ReportsPerMinute)).
-			Post("/reports", s.h.HandleReport())
+			Post("/api/v1/reports", s.h.HandleReport())
 	})
+
+	if s.params.Config.MetricsUsername != "" {
+		s.router.With(s.mw.MetricsAuth()).
+			Get("/metrics", promhttp.HandlerFor(
+				registry, promhttp.HandlerOpts{},
+			).ServeHTTP)
+	}
 }
@@ -107,6 +107,95 @@ func TestCORSAllowedOriginsReachTheRouter(t *testing.T) {
 	}
 }

+// TestNoMetricsWithoutCredentials: with neither metrics setting set,
+// there is no /metrics.
+func TestNoMetricsWithoutCredentials(t *testing.T) {
+	t.Setenv("METRICS_USERNAME", "")
+	t.Setenv("METRICS_PASSWORD", "")
+
+	srv := newServer(t)
+	srv.SetupRoutes()
+
+	rec := httptest.NewRecorder()
+	req := httptest.NewRequestWithContext(t.Context(),
+		http.MethodGet, "/metrics", http.NoBody)
+	srv.ServeHTTP(rec, req)
+
+	if rec.Code != http.StatusNotFound {
+		t.Fatalf("status = %d, want %d", rec.Code, http.StatusNotFound)
+	}
+}
+
+// TestMetricsBehindBasicAuth: with both metrics settings set, /metrics
+// answers only with them as basic auth credentials, and shows a
+// request to a route but not one to a path no route has.
+func TestMetricsBehindBasicAuth(t *testing.T) {
+	t.Setenv("METRICS_USERNAME", "prometheus")
+	t.Setenv("METRICS_PASSWORD", "right")
+
+	srv := newServer(t)
+	srv.SetupRoutes()
+
+	get := func(path, username, password string) *httptest.ResponseRecorder {
+		rec := httptest.NewRecorder()
+		req := httptest.NewRequestWithContext(t.Context(),
+			http.MethodGet, path, http.NoBody)
+
+		if username != "" {
+			req.SetBasicAuth(username, password)
+		}
+
+		srv.ServeHTTP(rec, req)
+
+		return rec
+	}
+
+	get("/.well-known/healthcheck", "", "")
+	get("/api/v1/no-such-route", "", "")
+
+	for _, creds := range [][2]string{
+		{"", ""},
+		{"prometheus", "wrong"},
+		{"someone", "right"},
+	} {
+		rec := get("/metrics", creds[0], creds[1])
+		if rec.Code != http.StatusUnauthorized {
+			t.Errorf("credentials %q: status = %d, want %d",
+				creds, rec.Code, http.StatusUnauthorized)
+		}
+	}
+
+	rec := get("/metrics", "prometheus", "right")
+	if rec.Code != http.StatusOK {
+		t.Fatalf("right credentials: status = %d, want %d",
+			rec.Code, http.StatusOK)
+	}
+
+	body := rec.Body.String()
+	if !strings.Contains(body, `handler="/.well-known/healthcheck"`) {
+		t.Errorf("metrics show no health check request:\n%s", body)
+	}
+
+	if strings.Contains(body, "no-such-route") {
+		t.Errorf("metrics show a request to a path no route has:\n%s", body)
+	}
+
+	if !strings.Contains(body, "go_goroutines") {
+		t.Errorf("metrics show no Go runtime metrics:\n%s", body)
+	}
+}
+
+// TestMetricsInTwoServers: two servers in one process can both have
+// metrics on.
+func TestMetricsInTwoServers(t *testing.T) {
+	t.Setenv("METRICS_USERNAME", "prometheus")
+	t.Setenv("METRICS_PASSWORD", "right")
+
+	for range 2 {
+		newServer(t).SetupRoutes()
+	}
+}
+
 // TestHealthCheckRejectsOversizeBody sends the health check, which
 // never reads its body, a body one byte over the limit. Only the
 // router-wide body limit can reject it.
@@ -68,4 +68,10 @@ server {
    location = /.well-known/healthcheck {
        proxy_pass http://127.0.0.1:8081;
    }
+
+    # The backend's Prometheus metrics, behind its own basic auth. Unless
+    # METRICS_USERNAME and METRICS_PASSWORD are set, it answers 404.
+    location = /metrics {
+        proxy_pass http://127.0.0.1:8081;
+    }
 }
@@ -17,11 +17,13 @@
 #
 # golangci-lint is not installed: make lint runs it in Docker, which
 # this script does not install either.
+#
+# Unlike the org model: Go and gcc for backend/, a newer node for eslint.
 set -eu

 ROOT="$(cd "$(dirname "$0")/.." && pwd -P)"

-# Pinned versions, 2026-07-07
+# Pinned versions, 2026-07-06
 NODE_VERSION="22.17.0"
 # The oldest node the frontend's dependencies accept: the "engines"
 # field of eslint 10.12.0, the most demanding of them, asks for 22.13.0
@@ -0,0 +1,13 @@
+#!/bin/sh
+# script/build: build the frontend for production into dist/. The Go
+# backend is built by backend/script/build.
+set -eu
+
+ROOT="$(cd "$(dirname "$0")/.." && pwd -P)"
+
+main() {
+    cd "$ROOT"
+    yarn build
+}
+
+main "$@"
@@ -0,0 +1,13 @@
+#!/bin/sh
+# script/dev: run the frontend's Vite dev server. It proxies /api to a
+# netwatch-server running locally (see vite.config.js).
+set -eu
+
+ROOT="$(cd "$(dirname "$0")/.." && pwd -P)"
+
+main() {
+    cd "$ROOT"
+    yarn dev
+}
+
+main "$@"
@@ -1,6 +1,7 @@
 #!/bin/sh
 # script/fmt: format the whole repo (writes): prettier over everything
 # it understands, then gofmt over the Go backend.
+# The org model formats only markdown; this repo also has JS and Go.
 set -eu

 ROOT="$(cd "$(dirname "$0")/.." && pwd -P)"
@@ -1,6 +1,7 @@
 #!/bin/sh
 # script/fmt-check: check formatting across the whole repo (read-only).
 # Same scope as script/fmt, but fails instead of writing.
+# The org model checks only markdown; this repo also has JS and Go.
 set -eu

 ROOT="$(cd "$(dirname "$0")/.." && pwd -P)"
@@ -1,7 +1,7 @@
 #!/bin/sh
 # script/frontend-fmt: format the frontend and every other file prettier
-# understands, repo-wide (writes). backend/ is in .prettierignore; Go
-# sources are formatted by backend/script/fmt.
+# understands, repo-wide (writes), the markdown in backend/ included.
+# Prettier does not read Go; backend/script/fmt formats the Go sources.
 set -eu

 ROOT="$(cd "$(dirname "$0")/.." && pwd -P)"
@@ -8,8 +8,8 @@ ROOT="$(cd "$(dirname "$0")/.." && pwd -P)"
 main() {
    cd "$ROOT"
    hook=".git/hooks/pre-commit"
-    printf '#!/bin/sh\nset -e\nscript/precommit\n' > "$hook"
-    chmod +x "$hook"
+    printf '#!/bin/sh\nset -e\nscript/precommit\n' > .git/hooks/pre-commit
+    chmod +x .git/hooks/pre-commit
    echo "pre-commit hook installed: runs script/precommit"
 }