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Serve Prometheus metrics at /metrics behind basic auth (closes #94)
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With METRICS_USERNAME and METRICS_PASSWORD both set, the backend
records request metrics through go-http-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.

Only requests chi has matched to a route 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
This commit is contained in:
sneak
2026-10-04 01:47:49 +00:00
parent 3b1262718d
commit a388121784
12 changed files with 252 additions and 34 deletions
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backend/README.md
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@@ -88,6 +88,8 @@ 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
@@ -102,16 +104,16 @@ 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.
@@ -176,6 +178,19 @@ 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 matches a
route, the metrics record its duration and response size, labelled with its
path, method and status; they also count the requests in progress, and include
Go's runtime and process metrics. A request to a path no route has, or with a
method its route does not take, is not recorded: clients can make up any number
of those, 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.
## TODO
- Add integration test that POSTs a report and verifies the compressed output