Fix Issue #604: Celery Beat Crashing at the End of Daylight Savings by polarmt · Pull Request #605 · celery/django-celery-beat

polarmt · 2022-11-11T19:00:12Z

Dependencies

celery/celery#7901

Note: The two PRs are codependent and need to be merged together.

Overview

This is my suggested fix for #604. The following issue assumes America/Los_Angeles.

Testing

All testing was done on the following versions:
django: 3.2.15
celery: 5.2.7
django-celery-beat: 2.4.0

USE_TZ is not set.

Reproducing the Issue

In the Django shell (python manage.py shell):

from datetime import datetime, timedelta
from celery.utils import time
from django_celery_beat.utils import make_aware
from pytz import timezone

dt  = datetime(2022, 11, 6, 1, 34, 0)
now = make_aware(dt)

Without the changes in this PR, this should throw an AmbiguousTimeError.

Behavior of `remaining` During Transition (Without celery/celery#7901)

We can run the following script to test how the Celery beat will calculate the time remaining during the transition:

from datetime import datetime, timedelta
from celery.utils import time
from django_celery_beat.utils import make_aware
from pytz import timezone

dt  = datetime(2022, 11, 6, 1, 34, 0)
now = make_aware(dt)

tz = timezone('America/Los_Angeles')
start = datetime(2022, 11, 6, 1, 15, 0)
start = tz.localize(start, is_dst=True)
ends_in = timedelta(minutes=80)

print(time.remaining(time.maybe_make_aware(start), ends_in, time.maybe_make_aware(now)))

now here would be 1:34 AM PST or 1:34:00-8:00 while start would be 1:15 AM PDT or 1:15:00-7:00. The correct return value of time.remaining(...) here would be 1 minute since 1 hour 20 minutes from start would be 1:35:00-8:00. The problem is that time.remaining(...) returns 1 hour 1 minute because time.remaining will convert 1:15:00-7:00 to 1:15-8:00.

Behavior of `remaining` During Transition (With celery/celery#7901)

We can use the same script as the above subsection after making the changes in celery/celery#7901. This will cause time.remaining(...) to return 1 minute instead of 1 hour 1 minute, which is the correct value.

auvipy

beside it will be very useful to have proper unit tests for this change

auvipy · 2022-11-12T04:32:46Z

django_celery_beat/utils.py

-            value = timezone.make_aware(value, timezone.get_default_timezone())
+            tm_isdst = time.localtime().tm_isdst
+
+            # tm_isdst may return -1 if it cannot be determined


I am not sure about this part, can any other way we can check it?

I referenced these posts 1 (top answer only) and 2. There are other suggested solutions online. I can summarize the problems with these solutions.

Use of localize

Source 1
Source 2
Source 3

The root cause was inside localize. Using the localize to fix the problem with localize sounds counterintuitive. For instance, link 1 mentions the following in the final solution:

Once you've **localized** a datetime in fact you can simply check it's .dst() method to see if it's zero.

time.daylight

Source

This solution might work, but the underlying code is just to do a similar check to what I do here. This code is cleaner, and I can change it if you would like.

Calculations

Source

One way is to calculate the timezone based on the current time and a previous time, but I think that this solution is long and too ad-hoc when we can achieve this with a few lines of code.

Conclusion

I think that time.daylight or time.localtime+tm_isdst is the best way to go for this. If you believe in the other solutions, please let me know.

I have to check to give you proper answer

Sounds good. Let me know when you've checked.

polarmt · 2022-11-14T19:54:55Z

beside it will be very useful to have proper unit tests for this change

I added the unit tests.

…g in None all the time

for more information, see https://pre-commit.ci

cclauss · 2023-12-19T21:30:48Z

Now that tests are passing on Django v5 this all becomes more difficult because:

Support for pytz timezones is removed.
The is_dst argument is removed from:
- QuerySet.datetimes()
- django.utils.timezone.make_aware()
- [ ... ]

https://docs.djangoproject.com/en/5.0/releases/5.0/#features-removed-in-5-0

cclauss · 2024-01-16T10:12:16Z

@polarmt Please rebase to resolve the git conflicts.

cclauss · 2024-03-04T14:23:23Z

@polarmt Tests are ~50/50 pass/fail and in Django v5 the default value of the USE_TZ setting is changed from False to True.

Now that we have release v2.6.0 that supports Django v5, how should we proceed with this effort?

auvipy

we need to fix the conflict and make the ci green as the related pr seems to be passing in celery

auvipy · 2025-05-18T03:49:26Z

@alirafiei75 sorry to ping you again here. since you are doing a lot recently, can you please check this PR and related celery issue, that if it is needed any more? if yes, if possible send a new pr with fixing the old codes?

alirafiei75 · 2025-05-18T06:57:37Z

@alirafiei75 sorry to ping you again here. since you are doing a lot recently, can you please check this PR and related celery issue, that if it is needed any more? if yes, if possible send a new pr with fixing the old codes?

Not a problem at all. Happy to help. I will check it in the upcoming week.

eht16 · 2025-10-28T21:09:56Z

@alirafiei75 any chance you might find time to update the PR to get it merged?

I was hit by this issue, or maybe celery/celery#6438 last weekend at the DST change.
The monitoring alerted because a Beat task wasn't executed for one hour at the DST change and caused me to get up in the night to check the alert 😢.

This was referenced Nov 11, 2022

Fix Issue #604 in django-celery-beat: Celery Beat Crashing at the End of Daylight Savings celery/celery#7901

Open

Celery Beat Crashing at the End of Daylight Savings #604

Open

auvipy requested changes Nov 12, 2022

View reviewed changes

polarmt force-pushed the master branch from 96d7e39 to c78baf9 Compare November 14, 2022 19:54

polarmt force-pushed the master branch 2 times, most recently from bc6f65c to b75637f Compare November 14, 2022 23:39

Andrew Yoo and others added 5 commits July 6, 2023 08:58

Add is_dst parameter based on time's tm_isdst field instead of passin…

a9d66a9

…g in None all the time

add unit tests

b0749b2

Add -1 case

e73f397

add line

d142f88

[pre-commit.ci] auto fixes from pre-commit.com hooks

6d51ddc

for more information, see https://pre-commit.ci

polarmt force-pushed the master branch from ef8e442 to 6d51ddc Compare July 6, 2023 15:58

Andrew Yoo added 5 commits July 6, 2023 10:14

format

789d16b

more formatting changes

6df332f

some more format optimizations

0a1fe8b

try this

c54d3c1

shorter line

a4a39c0

Merge branch 'main' into master

f723a74

auvipy requested changes Mar 29, 2025

View reviewed changes

This was referenced Apr 24, 2025

Period Tasks Don't Adjust for Daylight Savings #134

Open

Package not handling Daylight Savings Time #194

Open

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polarmt commented Nov 11, 2022 • edited Loading Uh oh! There was an error while loading. Please reload this page.

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Dependencies

Overview

Testing

Reproducing the Issue

Behavior of remaining During Transition (Without celery/celery#7901)

Behavior of remaining During Transition (With celery/celery#7901)

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auvipy Nov 12, 2022

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polarmt Nov 14, 2022

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Use of localize

time.daylight

Calculations

Conclusion

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auvipy Nov 14, 2022

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polarmt Nov 15, 2022

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polarmt commented Nov 14, 2022

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cclauss commented Jan 16, 2024

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auvipy commented May 18, 2025

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alirafiei75 commented May 18, 2025

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eht16 commented Oct 28, 2025

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polarmt commented Nov 11, 2022 •

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Behavior of `remaining` During Transition (Without celery/celery#7901)

Behavior of `remaining` During Transition (With celery/celery#7901)

Use of `localize`

`time.daylight`

cclauss commented Dec 19, 2023 •

edited

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cclauss commented Mar 4, 2024 •

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