What it is: The purpose-built serverless scheduler — cron, rate, or one-time invocation of 200+ AWS API targets. For “run X on a schedule,” this has replaced CloudWatch Events scheduled rules as the recommended answer.
Exam-testable facts:
- Occurrence types: one-time (
at(...)timestamp) or recurring (cron or rate expression). - Flexible time windows: OFF, or FLEXIBLE with a 1–1440 minute window — the invocation lands somewhere inside the window, which smooths out thundering-herd load and cost.
- Schedule groups: tag and organize schedules as a set.
- Timeframes: timezone-aware evaluation plus optional start/end dates (start date is ignored for one-time schedules).
- Reliability: per-target retry policy and an SQS dead-letter queue for failed invocations.
- Permissions: the scheduler assumes an execution role to invoke the target — the role, not the schedule creator, needs target permissions.
Common traps:
- “Run this Lambda every hour, but spread invocations over 15 minutes” → flexible time window, not a cron hack.
- Flexible window controls when within the window it fires; it is not a delay or a timeout.
- CloudWatch Events scheduled rules still exist, but new designs should use Scheduler.
Sources: https://docs.aws.amazon.com/eventbridge/latest/userguide/using-eventbridge-scheduler.html
Added during the 2026-10-03 review. All prose is original; facts verified against the AWS documentation links in Sources above.