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swarm-otel: scrape grafana through its published name

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Grafana's own metrics were scraped over loopback through the
`grafana-metrics` nginx vhost, declared only where grafana and the
collector share a host, so a collector on any other host had no job for
it. Its target is now declared on every host as
`https://<swarm.grafana.domain>/metrics`, next to the other published
targets, and grafana's vhost serves `= /metrics` behind the collector's
auth subrequest (`/__grafana_metrics_authz`, the forge's shape). The
rules derived from `publishedScrapeTargets` admit the collector's client
there and deny every other subject.

The loopback scrape is gone with the vhost that served it and its
`swarm.grafana.metricsPort` option, so a single host still scrapes
grafana once, now by name. A config that sets that option now fails
evaluation with "option does not exist".

On the published vhost `/metrics` was answered with 403 for everyone.
It now answers the collector's token, and a plain session gets authelia's
`deny`. The design note that ruled the published vhost out for scraping
predates the collector's credential; it is replaced by the location's
own comment and a line on `swarm.grafana.domain`.

Part of #5205
This commit is contained in:
atlas 2026-10-14 19:13:53 +02:00 • committed by mara
commit 54f6061d41
7 changed files with 145 additions and 99 deletions
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53
nix/host-modules/swarm-grafana-service.nix
View file

@ -1,7 +1,7 @@
# The swarm's metrics UI as every hive sees it: the name it is served under,
# the port its `/metrics` is re-served on, and the OIDC client it is
# registered as, identical on every host. What the host running it decides,
# and the container itself, are in ./swarm-grafana.nix.
# The swarm's metrics UI as every hive sees it: the name it is served under
# and the OIDC client it is registered as, identical on every host. What the
# host running it decides, and the container itself, are in
# ./swarm-grafana.nix.
{
lib,
config,
@ -20,12 +20,11 @@ in
# `enable` is `services.hyperhive.deploy.grafana.enable` — see
# ./deploy.nix. Whether this host runs the swarm's Grafana is a
# deployment decision, and `swarm.*` has to be identical on every host.
# Here is what the service IS to every hive: the name it is served under,
# the port its `/metrics` is re-served on, and the OIDC client it is
# registered as. What the host running it decides — which build it runs,
# where its datasources point, which plugins are in its store path, and
# the socket directory it shares with nginx — is `deploy.grafana`, in
# ./swarm-grafana.nix.
# Here is what the service IS to every hive: the name it is served under
# and the OIDC client it is registered as. What the host running it
# decides — which build it runs, where its datasources point, which plugins
# are in its store path, and the socket directory it shares with nginx — is
# `deploy.grafana`, in ./swarm-grafana.nix.
options.services.hyperhive.swarm.grafana = {
machine = lib.mkOption {
type = lib.types.str;
@ -51,35 +50,13 @@ in
⚠️ Changing this changes the OAuth redirect URI, which authelia
matches exactly. Both sides move together because both derive from
this option; an operator who pins one by hand breaks the login.
'';
};
metricsPort = lib.mkOption {
type = lib.types.port;
default = 9095;
description = ''
Loopback port on which the gateway's nginx re-serves Grafana's
`/metrics`, and nothing else, so the swarm's collector can scrape it.
⚠️ **This is nginx's port, not Grafana's.** Grafana still claims none —
see {option}`services.hyperhive.deploy.grafana.socketDir` for why that
matters. A prometheus scrape target is a `host:port`, and it cannot
address a unix socket; rather than undo the socket decision, the one
endpoint a scraper needs gets a listener of its own.
Bound to loopback and unauthenticated, which is the same posture every
other entry in
{option}`services.hyperhive.swarm.otel.scrapeTargets` has: those
targets are trusted by *proximity* rather than by credential.
Deliberately **not** the published `grafana.<domain>` vhost, which
would put an authorization decision in front of a scrape: that vhost
answers `/metrics` with 403, because Grafana serves it without
authentication.
The number itself is arbitrary and free today;
`state/eval-port-collisions.sh` is what keeps it that way, since a
second claim on a port in this shared namespace produces no bind error
and nothing in any log.
The swarm collector scrapes Grafana's own metrics at
`https://<this name>/metrics`, from whichever host it runs on.
Grafana serves that endpoint to anyone, so the gateway puts it
behind authelia, whose rules admit only the collector's OAuth2
client there: see `publishedScrapeTargets` in
./swarm-otel-service.nix.
'';
};