Measured · Updated
Kubernetes CronJobs at 1 a.m. run twice when US clocks go back on Sunday 1 November
On Sunday 1 November 2026 most of the US and eastern Canada set their clocks back at 02:00, so 01:00 to 01:59 local time happens twice. We ran Kubernetes' own CronJob scheduling code from v1.37.2, the current release, through that hour. A CronJob with timeZone: America/New_York and schedule: "30 1 * * *" created a Job at 01:30 EDT and a second Job at 01:30 EST, an hour later. The two Jobs get different names, so nothing stops the second one. Nightly backups, reports, exports and billing runs set between 01:00 and 01:59 would run twice.
CronJobs set before 01:00 or from 02:00 on ran once. Hourly CronJobs ran once for every hour that passed, which is what they should do.
Running clusters have already done this. When Europe's clocks went back on 25 October, a team running a 02:00 CronJob in Europe/Amsterdam wrote that it "started a run at 00:00 UTC and another at 01:00 UTC, and concurrencyPolicy: Replace ended the first after an hour of work". A Google Kubernetes Engine user reported the same double run in 2023 (kubernetes#121594); a bot closed that report without a fix.
The first of the two runs is at 05:30 UTC for a 01:30 job in New York and Toronto, 06:30 UTC in Chicago, 07:30 UTC in Denver and 08:30 UTC in Los Angeles. Make the change before then. Alberta, Manitoba and the Northwest Territories stop changing their clocks that day, but the time zone data in kube-controller-manager v1.37.2 still moves them back an hour (our Canada guide).
Check this today
List every CronJob with its time zone and schedule:
kubectl get cronjobs -A -o custom-columns='NAMESPACE:.metadata.namespace,NAME:.metadata.name,TIMEZONE:.spec.timeZone,LAST:.status.lastScheduleTime,SCHEDULE:.spec.schedule'Find the ones that run twice. A CronJob is affected when both are true:
- TIMEZONE is a zone that sets its clocks back on 1 November, such as
America/New_York,America/Toronto,America/Chicago,America/Denver,America/Los_AngelesorAmerica/Anchorage, or an older name for one of them such asUS/Eastern.America/Phoenixdoesn't change its clocks, andEtc/UTCdoesn't either; those ran once. - The hour in SCHEDULE includes 1. The hour is the second of the five fields:
30 1 * * *is 01:30. Look for an hour field that is1or includes it, such as0-3,1-5or1,13. Because 1 November is a Sunday and the 1st of the month, Sunday-only (0orSUNin the last field) and 1st-of-month (1in the third field) CronJobs are included.@daily,@weeklyand@monthlymean 00:00 and ran once.
TIMEZONE
<none>means the CronJob follows the time zone of kube-controller-manager, per the Kubernetes documentation. In our run, a30 1 * * *CronJob withouttimeZonecreated two Jobs when the controller ran in New York time and one when it ran in UTC. LAST is always shown in UTC, so a CronJob with a fixed hour tells you which: if LAST matches SCHEDULE, for example30 6 * * *and…T06:30:00Z, the controller runs in UTC and these CronJobs are not affected. If LAST is 4 to 9 hours later than SCHEDULE, the controller runs in a US time zone: check these CronJobs as if TIMEZONE were that zone.- TIMEZONE is a zone that sets its clocks back on 1 November, such as
Change each one you find, before Sunday. On a CronJob that already exists, moving the time later makes the controller start one catch-up Job for the new time it has just "missed". That Job can come as late as the old 01:30 run on Sunday, so a change made on Saturday can still give two Jobs on 1 November. The
startingDeadlineSecondsin the commands below stops the catch-up: with it, each change created one Job on 1 November in our run, whether we made it on Friday or on Saturday.Move it to 00:xx or to 03:00 or later, for example 03:30. Don't move it to 02:xx: on 14 March 2027, when the clocks go forward, 02:00 to 02:59 doesn't exist, and daily 02:00, 02:30 and 02:59 CronJobs created no Job that day in our run (below). 03:30 ran once on both days. A move to 00:xx needs no deadline, because the new time is earlier and there is nothing to catch up.
kubectl patch cronjob <name> -n <namespace> --type merge -p '{"spec":{"schedule":"30 3 * * *","startingDeadlineSeconds":300}}'Or set it in UTC:
timeZone: Etc/UTCand the UTC time.30 6 * * *in UTC is 01:30 in New York from Sunday, and 02:30 before Sunday and again after the clocks go forward on 14 March 2027, so the local time moves an hour at each change.kubectl patch cronjob <name> -n <namespace> --type merge -p '{"spec":{"timeZone":"Etc/UTC","schedule":"30 6 * * *","startingDeadlineSeconds":300}}'
With
startingDeadlineSeconds: 300, a run that the controller misses by more than 5 minutes, for example while the control plane is down, is skipped rather than started late.If the CronJob comes from a manifest, a Helm chart or a GitOps tool such as Argo CD or Flux, make the same change there, or the next sync puts the old schedule back. A release installed with Helm 4 may instead fail its next
helm upgradewith a conflict withkubectl-patchon.spec.schedule; it goes through when the chart has the same values as the patch. Run the list from step 1 again to check the new values.Settings that don't stop the double run on their own:
startingDeadlineSecondswithout a new time (we tested 200 seconds; both Jobs were created);concurrencyPolicy: Forbid, which in the controller code skips the second run only if the first Job is still running an hour later; andconcurrencyPolicy: Replace, which deletes the first Job if it is still running, as in the Amsterdam report. If you can't move a CronJob, make the job itself check whether it has already done that day's work, using the local date; we did not test this.
What we measured
We took the CronJob controller's scheduling file (pkg/) from Kubernetes v1.37.2 unchanged and called it the way the controller's sync loop does, once a minute on a clock stepped from 12:00 UTC the day before to 12:00 UTC the day after. A Job counted as created when the code returned a scheduled time that had not been used and whose Job name did not exist yet. This is the controller's decision code on a stepped clock, not a running cluster; we did not change the clock of a live cluster. Jobs created for 1 November 2026, by local date:
| CronJob | America/New_York | Chicago, Denver, Los Angeles, Anchorage, Toronto | America/Phoenix, Etc/UTC |
|---|---|---|---|
30 1 * * * | 2: 05:30 UTC (01:30 EDT) and 06:30 UTC (01:30 EST) | 2, an hour apart | 1 |
30 1 * * *, startingDeadlineSeconds: 200 | 2, the same two times | — | — |
0 1 * * *, 59 1 * * * | 2 each | 2 each | 1 each |
30 1 * * 0 (Sundays), 30 1 1 * * (1st of the month) | 2 each | 2 each | 1 each |
*/30 1 * * * | 4 instead of 2 | 4 | 2 |
0 0-3 * * * | 5 instead of 4 | 5 | 4 |
30 0 * * *, 0 2 * * *, 30 2 * * *, 30 3 * * * | 1 each | 1 each | 1 each |
@daily, @weekly, @monthly | 1 each | 1 each | 1 each |
0 * * * * (hourly) | 25, one per hour that passed | 25 | 24 |
30 1 * * 1-5 (weekdays) | 0: 1 November is a Sunday | 0 | 0 |
The same file is in v1.35.10, v1.36.6 and the main branch on 30 October, and v1.34.13 has the same scheduling functions. All of them use robfig/cron v3.0.1 for the schedule.
When the clocks go forward on 14 March 2027
In March 02:00 to 02:59 is skipped. Running the same code through 14 March 2027 in New York, daily 0 2 * * *, 30 2 * * * and 59 2 * * * CronJobs created no Job that day. Daily 00:30, 01:30, 03:00 and 03:30 created one, and so did 30 6 * * * in Etc/UTC. That is why the change above moves CronJobs to 00:xx or 03:00 and later, not to 02:xx.
Already ran twice?
If you are reading this after 1 November, list the Jobs with the time each was scheduled for:
kubectl get jobs -A -o custom-columns='NAMESPACE:.metadata.namespace,NAME:.metadata.name,SCHEDULED:.metadata.annotations.batch\.kubernetes\.io/cronjob-scheduled-timestamp,CREATED:.metadata.creationTimestamp' --sort-by=.metadata.creationTimestampTwo Jobs from the same CronJob with the same local time and two different offsets are the double run: 2026-11-01T01:30:00-04:00 and 2026-11-01T01:30:00-05:00 in New York, or -05:00 and -06:00 in Chicago. For a CronJob without timeZone, SCHEDULED is in UTC, so the pair is two times an hour apart, such as 2026-11-01T05:30:00Z and 2026-11-01T06:30:00Z with a controller in New York time. The number at the end of a Job's name counts minutes, so the two names differ by 60. Look soon: by default Kubernetes keeps only the last three successful Jobs of each CronJob. If the CronJob sets successful to 0 or 1, its Job template sets ttlSecondsAfterFinished, or it uses concurrencyPolicy: Replace, Kubernetes may already have deleted the first Job, so one Job in this list does not mean it ran once; check the job's own logs or output for a second run. Check what the second run did (emails, invoices, payments, exports, database writes), then make one of the changes above. The next time 01:xx repeats in the US is 7 November 2027, but the March change skips 02:xx CronJobs before then.
Where the fix stands
On 30 October we found no fix in Kubernetes for a CronJob inside the repeated hour. The 2023 report from a Google Kubernetes Engine user, kubernetes#121594, was closed as not planned by the project's triage bot in March 2024 with no reply from a maintainer. An open pull request from October 2026 changes how the controller catches up on missed schedules; it does not change the repeated hour. The CronJob documentation does not mention daylight saving time.
Plain cron on a server behaves differently: Debian's cron does not re-run jobs that fall into a repeated hour when the clock moves back by less than 3 hours.
What we tested
- Kubernetes v1.37.2
pkg/, unchanged, with robfig/cron v3.0.1 and the v0.37.2 Kubernetes libraries, built with Go 1.27.3 and no network. Time zones America/New_York, America/Toronto, America/Chicago, America/Denver, America/Los_Angeles, America/Anchorage, America/Phoenix and Etc/UTC, on 25 October and 1 November 2026 and on 14 March 2027.controller/ cronjob/ utils.go - A CronJob without
timeZone, with the controller's own time zone set to America/New_York and to UTC. With the controller in New York time,30 1 * * *created two Jobs on 1 November, like a CronJob withtimeZone: America/New_York; in UTC it created one. - Every kubectl command on this page, with kubectl v1.37.2, against a v1.37.2 API server and controller manager that we started ourselves on 30 October, with no nodes, so the Jobs' pods never ran: the CronJob list, both changes and the Job list with the scheduled time.
- With two 1 November Jobs created and their pods marked complete through the API. With
successfulthe controller deleted the 01:30 EDT Job once the 01:30 EST Job had finished, and the Job list showed one Job; with the default of 3 it showed both. A CronJob that had already run that day, moved to a time 10 minutes past, got a late Job withoutJobs History Limit: 1 startingDeadlineSecondsand none with it. kubectl v1.29.15 and v1.31.14 printed the same lists as v1.37.2. After a change withkubectl patch, Helm v3.22.1 put the old schedule back on the next upgrade; a release installed with Helm v4.3.1 failed to upgrade with a conflict. - Read from the source, not run: the v1.37.2 controller's sync loop (how it skips a time it has already used,
startingDeadlineSeconds,concurrencyPolicy), the Job name and the scheduled-time annotation, and the controller that deletes Jobs afterttlSecondsAfterFinished; v1.34.13, v1.35.10 and v1.36.6 and the main branch. - Not tested: a running cluster through a real clock change, managed control planes (GKE, EKS, AKS and others), CronJobs with old
TZ=values in the schedule created before Kubernetes rejected them, and zones outside North America.
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