AWS - EventBridge Scheduler Enum

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EventBridge Scheduler

EventBridge Scheduler

Amazon EventBridge Scheduler is a fully managed, serverless scheduler designed to create, run, and manage tasks at scale. It enables you to schedule millions of tasks across over 270 AWS services and 6,000+ API operations, all from a central service. With built-in reliability and no infrastructure to manage, EventBridge Scheduler simplifies scheduling, reduces maintenance costs, and scales automatically to meet demand. You can configure cron or rate expressions for recurring schedules, set one-time invocations, and define flexible delivery windows with retry options, ensuring tasks are reliably delivered based on the availability of downstream targets.

There is an initial limit of 1,000,000 schedules per region per account. Even the official quotas page suggests, "It's recommended to delete one-time schedules once they've completed."

Types of Schedules

Types of Schedules in EventBridge Scheduler:

1. One-time schedules – Execute a task at a specific time, e.g., December 21st at 7 AM UTC.
2. Rate-based schedules – Set recurring tasks based on a frequency, e.g., every 2 hours.
3. Cron-based schedules – Set recurring tasks using a cron expression, e.g., every Friday at 4 PM.

Two Mechanisms for Handling Failed Events:

1. Retry Policy – Defines the number of retry attempts for a failed event and how long to keep it unprocessed before considering it a failure.
2. Dead-Letter Queue (DLQ) – A standard Amazon SQS queue where failed events are delivered after retries are exhausted. DLQs help in troubleshooting issues with your schedule or its downstream target.

Targets

There are 2 types of targets for a scheduler templated (docs), which are commonly used and AWS made them easier to configure, and universal (docs), which can be used to call any AWS API.

Templated targets support the following services:

• CodeBuild – StartBuild
• CodePipeline – StartPipelineExecution
• Amazon ECS – RunTask
  • Parameters: EcsParameters
• EventBridge – PutEvents
  • Parameters: EventBridgeParameters
• Amazon Inspector – StartAssessmentRun
• Kinesis – PutRecord
  • Parameters: KinesisParameters
• Firehose – PutRecord
• Lambda – Invoke
• SageMaker – StartPipelineExecution
  • Parameters: SageMakerPipelineParameters
• Amazon SNS – Publish
• Amazon SQS – SendMessage
  • Parameters: SqsParameters
• Step Functions – StartExecution

Enumeration

# List all EventBridge Scheduler schedules
aws scheduler list-schedules

# List all EventBridge Scheduler schedule groups
aws scheduler list-schedule-groups

# Describe a specific schedule to retrieve more details
aws scheduler get-schedule --name <schedule_name>

# Describe a specific schedule group
aws scheduler get-schedule-group --name <group_name>

# List tags for a specific schedule (helpful in identifying any custom tags or permissions)
aws scheduler list-tags-for-resource --resource-arn <schedule_group_arn>

Privesc

In the following page, you can check how to abuse eventbridge scheduler permissions to escalate privileges:

AWS - EventBridge Scheduler Privesc

References

• https://docs.aws.amazon.com/scheduler/latest/UserGuide/what-is-scheduler.html