swarm-otel: scrape grafana through its published name

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

nix/host-modules/glue-otel-scrape-targets.nix

@@ -1,21 +1,20 @@
-# Glue: declare the loopback scrape targets of grafana and nats on the swarm's
+# Glue: declare the loopback scrape target of nats on the swarm's OTEL
-# OTEL collector, wherever one of them shares a host with it. Authelia is a
+# collector, wherever it shares a host with it. Authelia and grafana are
-# `publishedScrapeTargets` job (./swarm-otel-service.nix); a loopback job of
+# `publishedScrapeTargets` jobs (./swarm-otel-service.nix); a loopback job of
 # the same name fails ./swarm-otel.nix's job-name assertion.
 #
-# ONE FILE, TWO PAIRINGS — each service ← the collector, with the same shape.
+# ONE PAIRING — nats ← the collector. Deleting this leaves the collector not
-# Deleting this leaves the collector scraping none of them: no error, no
+# scraping nats: no error, no metrics.
-# metrics.
 #
-# Each target is gated on the service AND the collector being enabled here. The
+# The target is gated on the service AND the collector being enabled here. The
 # loopback address is only honest when both run on this host; a target nobody
-# can read asserts a collection that is not happening. Both services default
+# can read asserts a collection that is not happening. Both default from
-# from `deploy.allSwarmServices`, but `mkDefault` is an invitation to override,
+# `deploy.allSwarmServices`, but `mkDefault` is an invitation to override, so
-# so co-location is a property of the auto-deployed topology, not the modules.
+# co-location is a property of the auto-deployed topology, not the modules.
 #
 # ⚠️ Silent when split: separate hosts are separate evaluations with no shared
-# context, so a host running a service and no collector declares nothing and
+# context, so a host running nats and no collector declares nothing and
-# the collector's host never learns of the service. No error, no warning — a
+# the collector's host never learns of it. No error, no warning — a
 # healthy exporter and an empty dashboard. Not guardable from here.
 #
 # ⚠️ `swarm.otel`, not `hyperhive.otel` — two collectors one word apart, and only
@@ -33,7 +32,6 @@ let
 in
 {
   config.services.hyperhive.swarm.otel.scrapeTargets = {
-    grafana = withCollector "grafana" "127.0.0.1:${toString swarmCfg.grafana.metricsPort}";
     nats = withCollector "nats" "127.0.0.1:${toString swarmCfg.nats.metricsPort}";
   };
 }

nix/host-modules/swarm-grafana-service.nix

@@ -1,7 +1,7 @@
-# The swarm's metrics UI as every hive sees it: the name it is served under,
+# 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
+# and the OIDC client it is registered as, identical on every host. What the
-# registered as, identical on every host. What the host running it decides,
+# host running it decides, and the container itself, are in
-# and the container itself, are in ./swarm-grafana.nix.
+# ./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,
+  # 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
+  # and the OIDC client it is registered as. What the host running it
-  # registered as. What the host running it decides — which build it runs,
+  # decides — which build it runs, where its datasources point, which plugins
-  # where its datasources point, which plugins are in its store path, and
+  # are in its store path, and the socket directory it shares with nginx — is
-  # the socket directory it shares with nginx — is `deploy.grafana`, in
+  # `deploy.grafana`, in ./swarm-grafana.nix.
-  # ./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 {
+        The swarm collector scrapes Grafana's own metrics at
-      type = lib.types.port;
+        `https://<this name>/metrics`, from whichever host it runs on.
-      default = 9095;
+        Grafana serves that endpoint to anyone, so the gateway puts it
-      description = ''
+        behind authelia, whose rules admit only the collector's OAuth2
-        Loopback port on which the gateway's nginx re-serves Grafana's
+        client there: see `publishedScrapeTargets` in
-        `/metrics`, and nothing else, so the swarm's collector can scrape it.
+        ./swarm-otel-service.nix.
-
-        ⚠️ **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.
       '';
     };
 

nix/host-modules/swarm-grafana.nix

@@ -20,6 +20,7 @@ let
   networkCfg = config.services.hyperhive.network;
   hyperhiveCfg = config.services.hyperhive;
   gatewayCfg = hyperhiveCfg.gateway;
+  autheliaDomain = hyperhiveCfg.swarm.authelia.domain;
   baoCfg = hyperhiveCfg.swarm.bao;
   baoDeploy = deployCfg.bao;
 
@@ -459,12 +460,43 @@ in
       listen = gatewayCfg.lib.listen;
       extraConfig = gatewayCfg.lib.securityHeaders;
       # Grafana serves its Prometheus exposition to anyone, signed in or not
-      # (`metrics.enabled` below, no `basic_auth_*`), so the published name
+      # (`metrics.enabled` below, no `basic_auth_*`), so this location's auth
-      # refuses it; the scrape goes through the loopback `grafana-metrics`
+      # is the only gate on it. `=` is enough: nginx matches the decoded,
-      # vhost instead. `=` is enough: nginx matches the decoded, normalised
+      # normalised path, so `//metrics`, `/./metrics`, `/%6detrics` and
-      # path, so `//metrics`, `/./metrics`, `/%6detrics` and `/metrics?x` all
+      # `/metrics?x` all land here, and Grafana itself answers `/metrics/` with
-      # land here, and Grafana itself answers `/metrics/` with a login redirect.
+      # a login redirect.
-      locations."= /metrics".return = "403";
+      #
+      # The collector requests exactly this URL, declared as
+      # `publishedScrapeTargets.grafana` in ./swarm-otel-service.nix; the two
+      # must agree, since that string is also the token's audience. Authelia's
+      # rules for it admit the collector's client and deny every other subject
+      # (`metricsRules` in ./swarm-authelia.nix).
+      locations."= /metrics" = {
+        proxyPass = "http://unix:${socketPath}:/metrics";
+        extraConfig = ''
+          auth_request /__grafana_metrics_authz;
+        '';
+      };
+      # The subrequest, same shape as the forge's `= /__forge_metrics_authz`
+      # (./hive-forge/default.nix): no `error_page 401 =302`, so a scraper
+      # gets the 401 rather than a login page parsed as metrics.
+      locations."= /__grafana_metrics_authz" = {
+        proxyPass = "https://${autheliaDomain}/api/authz/auth-request";
+        # nixpkgs appends its OWN `Host $host` after extraConfig, which would
+        # override verifiedProxyTo's — see hive-gateway/vhost-lib.nix.
+        recommendedProxySettings = false;
+        extraConfig = ''
+          internal;
+          ${gatewayCfg.lib.verifiedProxyTo autheliaDomain}
+          proxy_pass_request_body off;
+          proxy_set_header Content-Length "";
+          proxy_set_header X-Original-Method $request_method;
+          proxy_set_header X-Original-URL $scheme://$http_host$request_uri;
+          proxy_set_header X-Forwarded-Proto $scheme;
+          proxy_set_header X-Forwarded-Host $http_host;
+          proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
+        '';
+      };
       locations."/" = {
         proxyPass = "http://unix:${socketPath}:/";
         proxyWebsockets = true;
@@ -480,29 +512,6 @@ in
       };
     };
 
-    # The scrape listener: Grafana's `/metrics` and nothing else, on loopback.
-    #
-    # No `serverName` and no TLS on purpose — this listener exists for exactly
-    # one client on the same host, so there is no name to match and nothing to
-    # verify. It is the only vhost here that is not reachable from outside the
-    # machine, and that is what lets it skip the authorization the published
-    # one carries.
-    #
-    # ⚠️ `= /metrics` is an EXACT match, not a prefix: it is the difference
-    # between exposing one endpoint and re-serving the whole of Grafana on an
-    # unauthenticated port. Widening it would be a silent authorization bypass,
-    # since nothing else about this block would have to change. The published
-    # vhost above refuses `/metrics`, so this listener is the only way to it.
-    services.nginx.virtualHosts."grafana-metrics" = {
-      listen = [
-        {
-          addr = "127.0.0.1";
-          port = cfg.metricsPort;
-        }
-      ];
-      locations."= /metrics".proxyPass = "http://unix:${socketPath}:/metrics";
-    };
-
     # Order the container after the host CA service so the bind source below
     # exists before nspawn sets the mount up.
     systemd.services."container@${cfg.machine}" = caTrust.containerOrdering;

nix/host-modules/swarm-otel-service.nix

@@ -362,5 +362,7 @@ in
     victoriametrics = "https://${vmCfg.domain}/metrics";
     # The vhost location is in ./swarm-victorialogs.nix.
     victorialogs = "https://${hyperhiveCfg.swarm.victorialogs.domain}/metrics";
+    # The vhost location is in ./swarm-grafana.nix.
+    grafana = "https://${hyperhiveCfg.swarm.grafana.domain}/metrics";
   };
 }

nix/module-eval/forge-placement.nix

@@ -138,16 +138,15 @@ let
         && !(refusedOver bare "deploy.forgejo.sso.clientSecretFile");
     }
     {
-      # Authelia is a published target; ./swarm-otel-identity.nix covers it.
+      # Authelia and grafana are published targets; ./swarm-otel-identity.nix
-      name = "a host running the collector, authelia, grafana and nats scrapes grafana and nats on loopback, authelia not";
+      # covers them.
+      name = "a host running the collector, authelia, grafana and nats scrapes nats on loopback, authelia and grafana not";
       ok =
         let
           t = servicesHere.services.hyperhive.swarm.otel.scrapeTargets;
           port = n: toString servicesHere.services.hyperhive.swarm.${n}.metricsPort;
         in
-        t.grafana == "127.0.0.1:${port "grafana"}"
+        t.nats == "127.0.0.1:${port "nats"}" && !(t ? authelia) && !(t ? grafana);
-        && t.nats == "127.0.0.1:${port "nats"}"
-        && !(t ? authelia);
     }
     {
       name = "hosting the swarm's shared services runs the forge";

nix/module-eval/grafana.nix

@@ -109,12 +109,6 @@ let
       && lib.hasInfix option a.message
     ) m.assertions;
   cases = [
-    {
-      name = "grafana declares no scrape target on a host with no collector";
-      ok =
-        !(grafanaOldPath.services.hyperhive.deploy.swarm-otel.enable)
-        && !(grafanaOldPath.services.hyperhive.swarm.otel.scrapeTargets ? grafana);
-    }
     {
       # The socket's directory is its access control, so it must stay dedicated
       # to this one socket. `readOnly` is what makes that inexpressible: a
@@ -124,22 +118,30 @@ let
       ok =
         !(builtins.tryEval grafanaSocketDirSet.services.hyperhive.deploy.grafana.socketDir).success
         &&
-          grafanaOldPath.services.nginx.virtualHosts."grafana-metrics".locations."= /metrics".proxyPass
+          grafanaOldPath.services.nginx.virtualHosts.${grafanaOldPath.services.hyperhive.swarm.grafana.domain}.locations."= /metrics".proxyPass
           == "http://unix:/run/swarm-grafana/grafana.sock:/metrics";
     }
     {
-      # Grafana serves `/metrics` unauthenticated, so the published name must
+      # Grafana serves `/metrics` unauthenticated, so the published name gates
-      # answer it itself; the scrape reads the loopback vhost above instead.
+      # it on the collector's auth subrequest: no `error_page 401 =302` (a
+      # scraper would parse a login page as metrics) and no `/__hive_authelia`.
       # `=` is what catches the normalised variants and still leaves the rest
       # of Grafana proxied.
-      name = "grafana's published vhost refuses /metrics and still proxies everything else";
+      name = "grafana's published vhost serves /metrics only behind the collector's auth subrequest";
       ok =
         let
           g = grafanaOldPath.services.hyperhive.swarm.grafana;
           locs = grafanaOldPath.services.nginx.virtualHosts.${g.domain}.locations;
+          checksOf = l: lib.filter (lib.hasPrefix "auth_request") (lib.splitString "\n" l.extraConfig);
+          authz = locs."= /__grafana_metrics_authz";
         in
-        locs."= /metrics".return == "403"
+        locs ? "= /metrics"
-        && locs."= /metrics".proxyPass == null
+        && locs."= /metrics".return == null
+        && checksOf locs."= /metrics" == [ "auth_request /__grafana_metrics_authz;" ]
+        && !(lib.hasInfix "error_page" locs."= /metrics".extraConfig)
+        && authz.proxyPass == "https://auth.t.local/api/authz/auth-request"
+        && lib.hasInfix "internal;" authz.extraConfig
+        && !(grafanaOldPath.services.nginx.virtualHosts ? "grafana-metrics")
         && lib.hasPrefix "http://unix:" locs."/".proxyPass;
     }
     {

nix/module-eval/swarm-otel-identity.nix

@@ -108,6 +108,7 @@ let
 
   forgeMetricsUrl = "https://forge.t.local/metrics";
   autheliaMetricsUrl = "https://auth.t.local/metrics";
+  grafanaMetricsUrl = "https://grafana.t.local/metrics";
   logsMetricsUrl = "https://logs.t.local/metrics";
   vmMetricsUrl = "https://metrics.t.local/metrics";
 
@@ -374,10 +375,11 @@ let
         lib.sort lib.lessThan (lib.attrValues h.swarm.otel.publishedScrapeTargets) == [
           autheliaMetricsUrl
           forgeMetricsUrl
+          grafanaMetricsUrl
           logsMetricsUrl
           vmMetricsUrl
         ]
-        && lib.length targets == 8
+        && lib.length targets == 10
         && lib.all (t: policy collector t == "one_factor") targets
         && lib.all (t: policy "user:someone" t == "deny") targets
         && lib.all (t: policy "group:admins" t == "deny") targets;
@@ -425,7 +427,7 @@ let
           ];
           matched = row: builtins.match re row.path != null;
         in
-        lib.length metricsRules == 6
+        lib.length metricsRules == 8
         && lib.all (r: r.resources == [ re ]) metricsRules
         && re == "^/metrics([?].*)?$"
         && lib.all (row: matched row == (row.nginx == "= /metrics")) table;
@@ -562,6 +564,63 @@ let
         && lib.length jobs == 1
         && (lib.head jobs).static_configs == [ { targets = [ "logs.t.local" ]; } ];
     }
+    {
+      name = "a collector on a host without grafana scrapes it by name";
+      ok =
+        let
+          s = otelSettings otelRemoteAuthelia;
+          job = lib.findFirst (j: j.job_name == "grafana") null s.receivers.prometheus.config.scrape_configs;
+        in
+        !otelRemoteAuthelia.services.hyperhive.deploy.grafana.enable
+        && job != null
+        && job.static_configs == [ { targets = [ "grafana.t.local" ]; } ]
+        && job.metrics_path == "/metrics"
+        && job.oauth2.endpoint_params.audience == grafanaMetricsUrl;
+    }
+    {
+      # The `deny` that confines grafana's `/metrics` is scoped to that path,
+      # and comes after the collector's rule: every other path on the name
+      # still reaches `default_policy`, as it did with no rule at all.
+      name = "authelia confines grafana's /metrics to the collector and leaves its other paths alone";
+      ok =
+        let
+          h = autheliaOnly.services.hyperhive;
+          collector = "oauth2:client:${h.swarm.otel.clientId}";
+          rules =
+            autheliaOnly.containers.swarm-authelia.config.services.authelia.instances.swarm.settings.access_control.rules;
+          grafanaRules = lib.filter (r: r.domain == "grafana.t.local") rules;
+          policy = subject: autheliaPolicy autheliaOnly subject "grafana.t.local";
+        in
+        map (r: r.policy) grafanaRules == [
+          "one_factor"
+          "deny"
+        ]
+        && lib.all (r: r.resources == [ "^/metrics([?].*)?$" ]) grafanaRules
+        && (lib.head grafanaRules).subject == [ collector ]
+        && policy collector "/metrics" == "one_factor"
+        && policy "user:someone" "/metrics" == "deny"
+        && policy "user:someone" "/metrics?x=1" == "deny"
+        && policy "group:admins" "/metrics" == "deny"
+        && policy "user:someone" "/" == "one_factor"
+        && policy "user:someone" "/login/generic_oauth" == "one_factor";
+    }
+    {
+      # Single host: grafana is scraped once, by its published name.
+      name = "a host running grafana and the collector scrapes it once, by name";
+      ok =
+        let
+          o = allLocal.services.hyperhive.swarm.otel;
+          jobs =
+            lib.filter (j: j.job_name == "grafana")
+              (otelSettings allLocal).receivers.prometheus.config.scrape_configs;
+        in
+        allLocal.services.hyperhive.deploy.grafana.enable
+        && allLocal.services.hyperhive.deploy.swarm-otel.enable
+        && !(o.scrapeTargets ? grafana)
+        && (o.publishedScrapeTargets.grafana or null) == grafanaMetricsUrl
+        && lib.length jobs == 1
+        && (lib.head jobs).static_configs == [ { targets = [ "grafana.t.local" ]; } ];
+    }
     {
       # Read against the roster the fixture declares rather than against
       # names spelled here: an arm naming `h1` passes on a single-hive