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To convert a standard five-field crontab schedule, map its minute, hour, day-of-month, month, and day-of-week fields into AWS’s six-field order, add a year field (usually *), use ? in the day field that should not constrain the schedule, and wrap the result in cron(...). Before deploying, check weekday numbering, timezone, and the exact cron dialect your existing job uses.
Convert the schedule field by field
- Separate the schedule from the command. In a crontab line, only the schedule fields belong in the AWS expression; the command that follows them does not. Confirm that the source is a five-field cron format rather than an implementation with extensions. The Linux crontab(5) manual documents Linux syntax, not every platform’s dialect.
- Keep the five common fields in order. Both formats begin with minute, hour, day-of-month, month, and day-of-week. EventBridge adds year as the sixth field, so its format is
cron(minutes hours day-of-month month day-of-week year). A year wildcard is usually*. See the AWS Scheduler cron-based schedules guide. - Resolve the two day fields. EventBridge does not allow day-of-month and day-of-week to both be specified as constraints in the same expression. Put
?in the field you do not intend to constrain. If the original schedule restricts both, it cannot be copied as one simple AWS expression; it may need multiple schedules or a redesigned schedule. - Use weekday names when numeric meanings are uncertain. EventBridge Scheduler accepts
1-7orSUN-SAT, with Sunday represented by 1. Other cron dialects may number weekdays differently, so translate numeric values only after confirming the source implementation’s convention. - Choose the timezone explicitly. Legacy EventBridge scheduled rules run in UTC+0. EventBridge Scheduler can use UTC or a configured timezone. If the old job follows local wall-clock time, choose the intended Scheduler timezone or deliberately convert its times to UTC.
- Validate before enabling it. Check the full expression and its upcoming run times in AWS before deployment. Legacy scheduled rules have one-minute precision; a rule can run within one minute of its specified start time, and delivery to its target can take several additional seconds.
Common crontab conversions
| Crontab schedule and intent | EventBridge expression | Notes |
|---|---|---|
0 12 * * *Daily at noon |
cron(0 12 * * ? *) |
Day-of-month remains unrestricted; day-of-week is not a constraint. AWS documents this daily pattern. |
0 18 * * 1-5Weekdays at 18:00 in a common numeric crontab dialect |
cron(0 18 ? * MON-FRI *) |
Weekday names avoid assuming that the source and AWS number weekdays alike. AWS documents this weekday expression. |
*/15 * * * *Every 15 minutes |
cron(0/15 * * * ? *) |
AWS uses 0/15 to express a 15-minute increment. |
| AWS-specific last-Friday example | cron(15 10 ? * 6L *) |
AWS documents 6L for the last Friday. This is an AWS-form example, not portable crontab syntax. |
These examples assume the stated intent and, where applicable, the stated source convention. They are not proof that a particular job will run at the same local time after migration; timezone and source-dialect differences still matter.
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Why a crontab expression can fail in EventBridge
It has five fields instead of six
A standard crontab schedule cannot be pasted unchanged: AWS requires the year field and the cron(...) wrapper. A common conversion starts by carrying over the first five fields in their existing order and appending the year value.
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EventBridge’s day-of-month/day-of-week rule is a frequent source of invalid expressions. Use ? where that day field should not specify a value. If the source requires conditions on both fields, decide whether separate schedules or a different schedule design can preserve the intended behavior.
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Weekday numbers mean something different
Do not assume numeric weekdays are portable. EventBridge Scheduler documents values 1–7 with Sunday first, while the source platform may use another convention. Replacing numbers with names such as MON-FRI makes the intended days clearer.
The source uses unsupported or special syntax
A Linux crontab manual is only a baseline for Linux. Check the actual source before converting macros, seconds, environment-variable assignments, extensions, or an expression that constrains both day fields. AWS supports lists, ranges, wildcards, increments, and applicable day-field operators including ?, L, W, and #. The # weekday form allows only one expression in that field. Consult AWS’s documented cron syntax for the supported forms.
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Choose cron or a rate expression
Use cron when the job follows calendar timing, such as a particular weekday and hour. For a simple repeated elapsed interval, AWS suggests considering a rate expression such as rate(5 minutes). A rate describes a regular interval; cron describes a customized calendar schedule.
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Choose the AWS scheduling feature for your timing needs
| Consideration | Legacy scheduled rules | EventBridge Scheduler |
|---|---|---|
| Timezone | UTC+0 | UTC or a timezone configured on the schedule |
| Precision and delivery | One-minute precision; target delivery may incur several seconds of delay | The cited AWS documentation supports timezone configuration; it does not establish a second-level execution guarantee |
| When to consider it | Existing scheduled-rule setups | AWS recommends Scheduler for scheduled invocation and describes it as more customizable, with broader target API operations and AWS service support |
AWS documents the differences in its scheduled rule guide and EventBridge Scheduler overview. The Scheduler guide describes cron as a way to create a fine-grained recurring schedule at a chosen time.
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Final checks before deployment
- Verify the original implementation and its weekday convention.
- Confirm that the AWS expression has six fields and the
cron(...)wrapper. - Use
?in the day field that should not constrain the schedule; do not specify both day fields as constraints. - Set or convert the timezone to preserve the intended wall-clock time.
- Review upcoming occurrences and allow for AWS’s documented precision and delivery timing rather than expecting second-level execution.
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