DINO-1093: fix counters in LASS to initialize all counters to 0 (must follow initialization rules, and unlike java, this is not automatic)

internal/leetcode-auth-stealer-service/src/prom.py

@@ -1,9 +1,34 @@
 """Prometheus collectors, typed metric updates, and exposition."""
 
-from typing import Literal
+from collections.abc import Iterable, Mapping, Sequence
+from typing import Literal, get_args
 
 from prometheus_client import CONTENT_TYPE_LATEST, Counter, generate_latest
 
+
+def _counter(
+    name: str,
+    documentation: str,
+    labelnames: Sequence[str] = (),
+    initial_labels: Iterable[Mapping[str, str]] = (),
+) -> Counter:
+    """
+    create a counter whose label combinations are exported at 0 before first use.
+
+    https://prometheus.io/docs/practices/the_zen/#avoid-missing-metrics
+    """
+    initial = list(initial_labels)
+    if labelnames and not initial:
+        raise ValueError(f"{name}: labeled counters must declare initial_labels")
+
+    counter = Counter(name, documentation, labelnames)
+
+    for labels in initial:
+        counter.labels(**labels)
+
+    return counter
+
+
 type AuthFailureReason = Literal[
     "invalid_argument",
     "bad_credentials",
@@ -15,10 +40,15 @@
     "incomplete_authentication",
 ]
 
-_AUTH_CALLS = Counter(
+_AUTH_CALLS = _counter(
     "leetcode_auth_calls_total",
     "Completed authentication calls by outcome and failure reason.",
     ("outcome", "reason"),
+    [{"outcome": "success", "reason": ""}]
+    + [
+        {"outcome": "failure", "reason": reason}
+        for reason in get_args(AuthFailureReason.__value__)
+    ],
 )