Stop logging /healthz and the internal SSR->API hop, truncate logged IPs

/healthz accounted for ~47% of prod's daily access log and the internal
frontend_ssr->backend content-API hop for another ~32%, each costing a
threadpool dispatch + lock + file write on the request path for traffic
that isn't meaningful to retain. classify_inbound gains "health" and
"internal" categories for these, both excluded from audit.log_access
(alongside the existing static/metrics/event exclusions) so they're never
dispatched to the logging threadpool at all.

The access log's client IP is now truncated to /24 (IPv4) or /48 (IPv6)
before being persisted -- coarse geo/abuse signal without keeping a full,
joinable address in Loki for the 30-day retention window, matching the
privacy page's claim that IPs aren't logged beyond normal request
handling. The rate limiter keyed off the same IP (_rate_ok) is untouched
and still sees full precision.

uvicorn's own --no-access-log now suppresses its duplicate per-request
line, since the app's own middleware already writes one.

backend/core/metrics.py

@@ -96,6 +96,12 @@ def classify_inbound(path: str, base: str = "") -> str:
     the app's mount prefix (e.g. ``/thermograph`` or ``""``).
     """
     p = path or "/"
+    # The liveness probe (Dockerfile HEALTHCHECK, Caddy health_uri) is by far the
+    # highest-volume single path in prod (measured ~47% of the access log) and is
+    # never real traffic — same posture as the metrics check below. Never under
+    # BASE (see /healthz's own docstring in web/app.py), so check before stripping.
+    if p.rstrip("/") == "/healthz":
+        return "health"
     # The dashboard polls the metrics endpoint; never count it as traffic, whatever base
     # prefix it arrives under — e.g. a `/thermograph/api/v2/metrics` probe against a
     # root-served prod app would otherwise land in "other" and show as an inbound error.
@@ -118,6 +124,13 @@ def classify_inbound(path: str, base: str = "") -> str:
         # category keeps record_inbound from double-counting every interaction.
         if seg == "event":
             return "event"
+        # The SSR content API (backend/api/content_routes.py) is called only by
+        # the frontend_ssr service's own api_client.py, never by a browser — a
+        # server-to-server hop, not a page view. Its own category is what lets
+        # that (measured ~32% of the access log on prod) be excluded from the
+        # access log below without also hiding real external traffic.
+        if seg == "content":
+            return "internal"
         return f"api:{seg}" if seg else "api:other"
     if p.endswith((".js", ".css", ".html", ".webmanifest", ".png", ".svg", ".ico",
                    ".json", ".woff", ".woff2", ".map", ".txt", ".xml")):

backend/deploy/entrypoint.sh

@@ -85,4 +85,7 @@ if [ "${RUN_MIGRATIONS:-1}" != "0" ]; then
 fi
 
 echo "==> Starting uvicorn on 0.0.0.0:${PORT:-8137} with ${WORKERS:-4} worker(s)"
-exec uvicorn app:app --host 0.0.0.0 --port "${PORT:-8137}" --workers "${WORKERS:-4}"
+# --no-access-log: the app's own request-logging middleware (audit.log_access,
+# web/app.py) already writes a structured line per request; uvicorn's own access
+# log just duplicated every one of them for no benefit.
+exec uvicorn app:app --host 0.0.0.0 --port "${PORT:-8137}" --workers "${WORKERS:-4}" --no-access-log

backend/tests/core/test_metrics.py

@@ -40,6 +40,16 @@ def test_classify_inbound_categories():
     # dashboard probing /thermograph/... against a root-served (base="") prod app.
     assert c("/thermograph/api/v2/metrics", "") == "metrics"
     assert c("/api/v2/metrics", "") == "metrics"
+    # The SSR content API (backend/api/content_routes.py) is a server-to-server
+    # hop from frontend_ssr's own api_client.py, never a browser -- its own
+    # category is what lets it be excluded from the access log without also
+    # hiding real external traffic under the generic "api:*" bucket.
+    assert c("/thermograph/api/v2/content/hub", "/thermograph") == "internal"
+    assert c("/api/v2/content/city/tokyo", "") == "internal"
+    # The liveness probe: never under BASE, whatever base the app happens to be
+    # mounted at (it's registered at a fixed path -- see web/app.py's healthz).
+    assert c("/healthz") == "health"
+    assert c("/healthz", "/thermograph") == "health"
     # pages, static, seo
     assert c("/thermograph/", "/thermograph") == "page"
     assert c("/thermograph/calendar", "/thermograph") == "page"

backend/tests/web/test_request_logging.py

@@ -0,0 +1,87 @@
+"""The request-logging middleware (web/app.py's revalidate_static): what gets
+counted, what gets written to the access log, and what gets truncated before
+it's persisted. Companion to core/test_metrics.py's classify_inbound tests --
+these exercise the actual ASGI request path, not just the classifier function.
+"""
+import pytest
+from fastapi.testclient import TestClient
+
+from web import app as appmod
+
+metrics = appmod.metrics   # the exact module object app.py's own calls use --
+audit = appmod.audit       # see the note on module-reload isolation below.
+
+
+@pytest.fixture
+def client():
+    return TestClient(appmod.app)
+
+
+def _patch_log_access(monkeypatch):
+    calls = []
+    monkeypatch.setattr(audit, "log_access", lambda record: calls.append(record))
+    return calls
+
+
+def test_healthz_is_never_audited(monkeypatch, client):
+    """/healthz is ~47% of prod's daily access log; it must never even reach
+    audit.log_access (not just be cheap once there -- see classify_inbound's
+    "health" category and the exclusion in revalidate_static)."""
+    calls = _patch_log_access(monkeypatch)
+    r = client.get("/healthz")
+    assert r.status_code == 200
+    assert calls == []
+
+
+def test_internal_category_is_never_audited(monkeypatch, client):
+    """The SSR content API's own category ("internal") is excluded from the
+    access log the same way -- it's a server-to-server hop (frontend_ssr's
+    api_client.py calling backend), not a page view."""
+    calls = _patch_log_access(monkeypatch)
+    monkeypatch.setattr(metrics, "classify_inbound", lambda path, base: "internal")
+    r = client.get("/thermograph/api/version")
+    assert r.status_code == 200
+    assert calls == []
+
+
+def test_access_log_ip_is_truncated_not_raw(monkeypatch, client):
+    calls = _patch_log_access(monkeypatch)
+    r = client.get("/thermograph/api/version",
+                    headers={"X-Forwarded-For": "203.0.113.77, 10.0.0.1"})
+    assert r.status_code == 200
+    assert len(calls) == 1
+    assert calls[0]["ip"] == "203.0.113.0"      # /24, not the exact address
+    assert calls[0]["ip"] != "203.0.113.77"
+
+
+def test_loggable_ip_truncation():
+    assert appmod._loggable_ip("203.0.113.77") == "203.0.113.0"
+    assert appmod._loggable_ip("2001:db8:1234:5678::1") == "2001:db8:1234::"
+    assert appmod._loggable_ip(None) is None
+    assert appmod._loggable_ip("") == ""
+    assert appmod._loggable_ip("not-an-ip") == "not-an-ip"   # best-effort, never raises
+
+
+def test_rate_limiter_still_sees_the_full_precision_ip(monkeypatch, client):
+    """_client_ip (which feeds both the access log and the event rate limiter)
+    is never itself truncated -- only what audit.log_access persists is. A
+    /24-truncated rate-limit key would let one abuser exhaust a whole NAT'd
+    office's quota, which is exactly what must NOT happen here."""
+    seen = {}
+    monkeypatch.setattr(metrics, "record_event", lambda name, **kw: seen.update(kw))
+    r = client.post("/thermograph/api/v2/event", json={"event": "home.locate"},
+                    headers={"X-Forwarded-For": "203.0.113.77"})
+    assert r.status_code == 204
+    assert seen["ip"] == "203.0.113.77"
+
+
+def test_event_route_records_end_to_end(client):
+    """Full HTTP round trip through the real ASGI route -- confirms the write
+    path backend/api/event -> metrics.record_event -> the counters store works
+    end to end (the existing suite only ever called record_event directly)."""
+    before = metrics.snapshot()["events_total"]
+    r = client.post("/thermograph/api/v2/event", json={"event": "home.locate"})
+    assert r.status_code == 204
+    after = metrics.snapshot()
+    assert after["events_total"] == before + 1
+    assert after["events"]["home.locate"]["direct"]   # no Referer sent -> "direct"

backend/web/app.py

@@ -3,6 +3,7 @@ import contextlib
 import datetime
 import hashlib
 import hmac
+import ipaddress
 import json
 import os
 import queue
@@ -263,13 +264,34 @@ def api_version():
 
 def _client_ip(request) -> "str | None":
     """The real client IP: the left-most X-Forwarded-For hop when a proxy fronts us
-    (Caddy on prod sets it), otherwise the direct peer address (LAN dev)."""
+    (Caddy on prod sets it), otherwise the direct peer address (LAN dev). Full
+    precision — the rate limiter (metrics._rate_ok) needs the exact address, since
+    a truncated key would let one abuser exhaust a whole NAT'd office's quota.
+    Truncate at the point of persistence instead (see _loggable_ip)."""
     xff = request.headers.get("x-forwarded-for")
     if xff:
         return xff.split(",")[0].strip()
     return request.client.host if request.client else None
 
 
+def _loggable_ip(ip: "str | None") -> "str | None":
+    """Coarsen a client IP before it's written to the access log: /24 for IPv4,
+    /48 for IPv6. Keeps rough geo/abuse signal without keeping a full, joinable
+    address sitting in structured logs for the log's 30-day retention -- the
+    public privacy page promises IPs aren't logged beyond normal request handling,
+    and a raw address shipped to Loki was a live gap against that. Never the
+    input to the rate limiter (_client_ip's callers pass the untruncated value
+    there) -- this is only what gets persisted."""
+    if not ip:
+        return ip
+    try:
+        addr = ipaddress.ip_address(ip)
+    except ValueError:
+        return ip  # not a parseable address (e.g. a test/placeholder value) -- pass through
+    prefix = 24 if addr.version == 4 else 48
+    return str(ipaddress.ip_network(f"{addr}/{prefix}", strict=False).network_address)
+
+
 @app.middleware("http")
 async def revalidate_static(request, call_next):
     """Serve the frontend with no-cache (NOT no-store): browsers may keep a copy
@@ -288,11 +310,15 @@ async def revalidate_static(request, call_next):
         # loop so one request's instrumentation can't stall every other request
         # this worker is serving concurrently.
         await run_in_threadpool(metrics.record_inbound, cat, response.status_code)
-        # Retain per-request client IPs for later analysis; skip static assets and the
-        # dashboard's own metrics polling to keep the log to real, meaningful traffic.
-        if cat not in ("static", "metrics", "event"):
+        # Retain per-request client IPs for later analysis; skip static assets, the
+        # dashboard's own metrics polling, the liveness probe (health -- by far the
+        # highest-volume single path, and never real traffic), and the internal
+        # SSR->API hop (internal -- frontend_ssr's own server-to-server calls, not
+        # a page view) to keep the log to real, meaningful traffic. The IP itself is
+        # truncated (see _loggable_ip) -- coarse geo/abuse signal, not a full address.
+        if cat not in ("static", "metrics", "event", "health", "internal"):
             await run_in_threadpool(audit.log_access, {
-                "ip": _client_ip(request), "method": request.method,
+                "ip": _loggable_ip(_client_ip(request)), "method": request.method,
                 "path": path, "status": response.status_code, "cat": cat})
         # Threshold-gated slow-request line: RunAudit only times the 7 graded
         # endpoints, so this is the only latency signal for auth/account/content