feat(traefik): Routers widget shows current routers only, one header row, certs on the routers they serve (#5254)

#5254 "Traefik — Routers: current routers only, header row, certs on the router they serve".

- Router hosts come from Traefik's API (/api/http|tcp/routers), read
  best-effort on each scrape. An optional api_url overrides it; the default
  is /api on the metrics host. A certificate's expiry then shows in a TLS
  column on the router whose host it covers. An expiring one makes that
  router a problem, graded by Settings → Thresholds.
- Only current: routers and certificates must have appeared in the last
  three scrapes. Certificates are upserted by serial and never deleted, so
  renewed or retired ones lingered on the widget.
- Widget order: verdict, problem routers with the reason, then the busiest
  healthy routers under one header (Router / Req/s / Bandwidth / p95 / TLS).
  A missing value shows "—".
- If the API is unreachable, expiring certificates are listed after the
  routers, not above them.
- The page splits certificates into served (with the routers using each,
  plus SANs) and "No longer served".
- Latest row per router: an index walk (recursive CTE + LATERAL) replaces
  DISTINCT plus a query per router.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tests/plugins/traefik/test_traefik_page.py

@@ -48,10 +48,10 @@ async def test_the_page_leads_with_problems_and_folds_the_healthy(app):
     problems, healthy = split_routers([
         _router("api", _latest(e5=3.0)), _router("web", _latest()), _router("docs", _latest())])
     now = datetime.now(timezone.utc)
-    certs = [{"serial": "1", "cn": "soon.example", "sans": [], "not_after": now + timedelta(days=2),
-              "days_remaining": 2.0},
-             {"serial": "2", "cn": "fine.example", "sans": [], "not_after": now + timedelta(days=60),
-              "days_remaining": 60.0}]
+    certs = [{"serial": "1", "cn": "soon.example", "sans": [], "routers": None,
+              "not_after": now + timedelta(days=2), "days_remaining": 2.0},
+             {"serial": "2", "cn": "fine.example", "sans": [], "routers": None,
+              "not_after": now + timedelta(days=60), "days_remaining": 60.0}]
     async with app.test_request_context("/plugins/traefik/rows"):
         page = await render_plugin_template(app, "traefik", "traefik/rows.html", problems=problems,
                                             healthy=healthy, global_stat=None, certs=certs, range_key="24h",
@@ -110,3 +110,123 @@ async def test_the_traffic_empty_state_knows_whether_the_log_is_on(app, enabled,
                                             range_key="24h", access_log_enabled=enabled,
                                             access_log_path="/var/log/traefik/access.log")
     assert says in page and not_says not in page
+
+
+# ── Routers widget: current routers, certs on the router they serve (#5254) ──
+
+@pytest.mark.parametrize("rule, hosts", [
+    ("Host(`app.example.com`)", ["app.example.com"]),
+    ("Host(`a.example.com`, `B.example.com`) && PathPrefix(`/api`)", ["a.example.com", "b.example.com"]),
+    ("Host(`a.example.com`) || Host(`b.example.com`)", ["a.example.com", "b.example.com"]),
+    ("HostSNI(`db.example.com`)", ["db.example.com"]),
+    ("HostSNI(`*`)", []),
+    ("PathPrefix(`/`)", []),
+    ("", []),
+])
+def test_a_router_rule_names_its_hosts(rule, hosts):
+    from plugins.traefik.scraper import rule_hosts
+    assert rule_hosts(rule) == hosts
+
+
+def test_a_certificate_covers_its_names_and_one_wildcard_label():
+    from plugins.traefik.scraper import cert_names, covers
+    names = cert_names("Example.com", "*.example.com, www.other.org")
+    assert names == {"example.com", "*.example.com", "www.other.org"}
+    assert covers(names, "example.com") and covers(names, "app.example.com")
+    assert covers(names, "www.other.org")
+    assert not covers(names, "a.b.example.com") and not covers(names, "other.org")
+
+
+@pytest.mark.parametrize("metrics_url, api_url, base", [
+    ("http://traefik:8080/metrics", "", "http://traefik:8080/api"),
+    ("http://traefik:8080/metrics?x=1", "", "http://traefik:8080/api"),
+    ("http://traefik:8080/metrics", "http://other:9000/api/", "http://other:9000/api"),
+])
+def test_the_api_sits_beside_the_metrics_unless_configured(metrics_url, api_url, base):
+    from plugins.traefik.scraper import api_base
+    assert api_base(metrics_url, api_url) == base
+
+
+def test_a_metrics_router_finds_its_api_name_with_or_without_the_entrypoint():
+    from plugins.traefik.routes import router_hosts
+    domains = {"app@docker": ["app.example.com"]}
+    assert router_hosts("app@docker", domains) == ["app.example.com"]
+    assert router_hosts("websecure-app@docker", domains) == ["app.example.com"]
+    assert router_hosts("myapp@docker", domains) == []
+
+
+def _cert(serial, cn, days, seen_ago=30, sans=None):
+    now = datetime.now(timezone.utc)
+    return NS(serial=serial, cn=cn, sans=sans, not_after=now + timedelta(days=days),
+              scraped_at=now - timedelta(seconds=seen_ago))
+
+
+def test_a_certificate_traefik_stopped_reporting_is_old_not_current():
+    from plugins.traefik.routes import current_certs
+    live, renewed = _cert("1", "a.example", 80), _cert("2", "a.example", 5, seen_ago=3600)
+    served, old = current_certs([live, renewed], 60)
+    assert served == [live] and old == [renewed]
+    assert current_certs([], 60) == ([], [])
+
+
+def test_each_router_gets_the_soonest_certificate_for_its_hosts():
+    from plugins.traefik.routes import certs_by_router
+    now = datetime.now(timezone.utc)
+    certs = [_cert("1", "*.example.com", 40), _cert("2", "app.example.com", 10), _cert("3", "x.org", 2)]
+    got = certs_by_router(["app@docker", "docs@docker", "plain@docker"],
+                          {"app@docker": ["app.example.com"], "docs@docker": ["docs.example.com"]},
+                          certs, now)
+    assert got["app@docker"]["cn"] == "app.example.com" and int(got["app@docker"]["days"]) == 9
+    assert got["docs@docker"]["cn"] == "*.example.com"
+    assert "plain@docker" not in got
+
+
+async def test_the_widget_gives_a_verdict_then_routers_under_one_header(app):
+    slow = _router("api@docker", _latest(p95=450.0))
+    expiring = _router("shop@docker", _latest(req=3.0))
+    expiring.update(state="crit", why="certificate expires in 2 days",
+                    cert={"cn": "shop.example", "days": 2.0, "grade": "crit"})
+    fine = _router("web@docker", _latest(req=9.0))
+    fine["cert"] = {"cn": "web.example", "days": 60.0, "grade": "ok"}
+    async with app.test_request_context("/plugins/traefik/widget"):
+        page = await render_plugin_template(
+            app, "traefik", "traefik/widget.html", problems=[expiring, slow], healthy=[fine],
+            healthy_more=4, total=7, loose_certs=[], domains_known=True)
+    page = " ".join(page.split())
+    assert "2 of 7 routers need a look." in page
+    assert page.count("<th>Router</th>") == 1 and "<th>TLS</th>" in page
+    # Problems first, each with why; the cert sits on its router, not above.
+    assert page.index(">shop") < page.index(">api") < page.index(">web")
+    assert "certificate expires in 2 days" in page and "p95 latency is 450 ms" in page
+    assert "60 days" in page and "Certificates expiring" not in page
+    assert '</span>shop<span class="w-sub' in page and ">shop@docker" not in page  # provider off the label
+    assert "+4 more healthy" in page
+
+
+async def test_without_router_domains_expiring_certs_follow_the_routers(app):
+    fine = _router("web@docker", _latest())
+    async with app.test_request_context("/plugins/traefik/widget"):
+        page = await render_plugin_template(
+            app, "traefik", "traefik/widget.html", problems=[], healthy=[fine], healthy_more=0, total=1,
+            loose_certs=[{"cn": "old.example", "days": 5.0}], domains_known=False)
+    page = " ".join(page.split())
+    assert "All 1 router healthy; 1 certificate expiring." in page
+    assert "<th>TLS</th>" not in page
+    assert page.index("<th>Router</th>") < page.index("Certificates expiring") < page.index("old.example")
+
+
+async def test_the_page_sets_certificates_traefik_no_longer_serves_apart(app):
+    now = datetime.now(timezone.utc)
+    certs = [{"serial": "1", "cn": "app.example", "sans": ["www.app.example"], "routers": ["app"],
+              "not_after": now + timedelta(days=40), "days_remaining": 40.0},
+             {"serial": "2", "cn": "spare.example", "sans": [], "routers": [],
+              "not_after": now + timedelta(days=40), "days_remaining": 40.0}]
+    old = [{"serial": "3", "cn": "gone.example", "sans": [], "routers": [],
+            "not_after": now + timedelta(days=5), "days_remaining": 5.0}]
+    async with app.test_request_context("/plugins/traefik/rows"):
+        page = await render_plugin_template(app, "traefik", "traefik/rows.html", problems=[], healthy=[],
+                                            gone=[], global_stat=None, certs=certs, old_certs=old,
+                                            range_key="24h", error_4xx=1.0, error_5xx=0.1)
+    page = " ".join(page.split())
+    assert "also www.app.example" in page and ">app</td>" in page and ">not in use</td>" in page
+    assert page.index("spare.example") < page.index("No longer served (1)") < page.index("gone.example")