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fix(crons): Compute next_checkin_latest in UTC during DST fold #128740

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fix(crons): Compute next_checkin_latest in UTC during DST fold #128740

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8e596bc
fix(crons): Compute next_checkin_latest in UTC during DST fold
spawnia Oct 25, 2026
8a19828
test(crons): Compare the fold=1 next check-in in UTC
spawnia Oct 25, 2026
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5 changes: 3 additions & 2 deletions src/sentry/monitors/models.py
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Original file line number Diff line number Diff line change
Expand Up @@ -4,7 +4,7 @@
import uuid
import zoneinfo
from collections.abc import Sequence
from datetime import datetime
from datetime import UTC, datetime
from functools import cache
from typing import TYPE_CHECKING, ClassVar, Self, override
from uuid import uuid4
Expand Down Expand Up @@ -353,7 +353,8 @@ def get_next_expected_checkin_latest(self, last_checkin: datetime) -> datetime:
"""
from sentry.monitors.utils import get_checkin_margin

next_checkin = self.get_next_expected_checkin(last_checkin)
# Add the margin in UTC: local wall-clock arithmetic drops the DST fold
next_checkin = self.get_next_expected_checkin(last_checkin).astimezone(UTC)
return next_checkin + get_checkin_margin(self.config.get("checkin_margin"))

def update_config(self, config_payload, validated_config):
Expand Down
22 changes: 22 additions & 0 deletions tests/sentry/monitors/test_models.py
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Expand Up @@ -71,6 +71,28 @@ def test_next_run_latest_crontab_with_margin(self) -> None:
2019, 1, 1, 1, 16, tzinfo=timezone.utc
)

def test_next_run_latest_crontab_during_dst_fold(self) -> None:
# Europe/Berlin repeats 02:00-02:59 local time on 2024-10-27 from 01:00 UTC
ts = datetime(2024, 10, 27, 1, 0, 3, tzinfo=timezone.utc)
monitor = Monitor(
config={
"schedule_type": ScheduleType.CRONTAB,
"schedule": "* * * * *",
"timezone": "Europe/Berlin",
"checkin_margin": 5,
"max_runtime": None,
}
)
monitor_environment = MonitorEnvironment(monitor=monitor, last_checkin=ts)

# PEP 495: inter-zone == is always False for a time with fold=1
assert monitor_environment.monitor.get_next_expected_checkin(ts).astimezone(
timezone.utc
) == datetime(2024, 10, 27, 1, 1, tzinfo=timezone.utc)
assert monitor_environment.monitor.get_next_expected_checkin_latest(ts) == datetime(
2024, 10, 27, 1, 6, tzinfo=timezone.utc
)

def test_next_run_crontab_with_timezone(self) -> None:
ts = datetime(2019, 1, 1, 1, 10, 20, tzinfo=timezone.utc)
monitor = Monitor(
Expand Down
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