EventBridge Scheduler

Standalone scheduler service — at, rate, cron expressions, SQS targets, DLQ routing, one-shot self-delete.

fakecloud implements the full EventBridge Scheduler surface (scheduler.amazonaws.com). This is a different service from EventBridge Rules — it ships in its own SDK (@aws-sdk/client-scheduler) and has its own data model (Schedule, ScheduleGroup, FlexibleTimeWindow, DeadLetterConfig, ActionAfterCompletion).

Supported features

  • Schedules — at(yyyy-mm-ddThh:mm:ss) one-shot, rate(N unit) recurring, cron(...) recurring
  • Schedule groups — create/get/delete/list; a default group is seeded per account and cannot be deleted
  • Targets — SQS (with Target.Input JSON), SNS, Lambda, Step Functions, EventBridge; Target.RoleArn is accepted (STS assume-role is a no-op in fakecloud)
  • Flexible time window — OFF and FLEXIBLE modes; MaximumWindowInMinutes is required when FLEXIBLE
  • ActionAfterCompletion: DELETE — one-shot at(...) schedules self-delete after firing
  • Dead-letter routing — when target delivery fails (e.g. queue missing), the Target.Input is forwarded to DeadLetterConfig.Arn with X-Amz-Scheduler-* metadata attributes (Attempt, Schedule-Arn, Target-Arn, Error-Code, Error-Message, Group)
  • Tagging — TagResource / UntagResource / ListTagsForResource on schedule groups
  • IAM enforcement — scheduler:* actions, scheduler:ScheduleGroup condition key, aws:ResourceTag/* + aws:RequestTag/* ABAC

Protocol

REST-JSON protocol over scheduler.<region>.amazonaws.com endpoint. SigV4 credential scope: scheduler/aws4_request.

Introspection

  • GET /_fakecloud/scheduler/schedules — list every schedule across all accounts
  • POST /_fakecloud/scheduler/fire/{group}/{name} — fire a specific schedule immediately (bypasses the wall-clock tick)

Cross-service delivery

Scheduler shares fakecloud's cross-service delivery bus, so targets resolve to live SNS / SQS / Lambda / StepFunctions / EventBridge implementations — the same plumbing that powers EventBridge Rules.

Firing semantics

  • Tick rate: 1 second. Every enabled schedule is evaluated against the current wall clock each tick.
  • Cron grammar: simplified six-field (min hour dom month dow year). Wildcards (* / ?) and single numeric values only — ranges (1-3), lists (1,3,5), and step values (*/5) are rejected rather than silently broadened, so unsupported schedules never fire instead of firing every minute.
  • Dedup: cron schedules dedupe by (year, ordinal, hour, minute), so daily/weekly crons fire every matching day.
  • FIFO SQS targets: a dedup ID is synthesized per fire (UUID, 36 chars — well under SQS's 128-char limit) so messages aren't dropped for FIFO queues that lack content-based dedup.

Non-goals

  • KMS encryption on schedule state
  • Cross-account target delivery (use the single-account surface)
  • End-to-end IAM policy evaluation beyond the existing test/test root bypass

Source