The timetable that runs your cron jobs

A schedule is a small saved object: an expression that says when, an optional time zone, a target that says what to call, and an execution role that gives Scheduler permission to call it. There are no servers or clocks for you to run. AWS launched it on 10 November 2022 and recommends it over the older EventBridge scheduled rules for anything time-based.

1. Expression

   at(), rate() or cron(), evaluated in UTC unless you name an IANA time zone.

2. Time window

   Required setting. OFF fires on the minute; FLEXIBLE fires within a window you set, which spreads load.

3. Execution role

   An IAM role that trusts scheduler.amazonaws.com and allows the one call the target needs.

4. Target

   One AWS API call, with up to 256 KB of input. Delivery is at-least-once.

• ? means “any”. One of the two day fields must be ?; you cannot put * in both.
• # picks the nth weekday of the month, and only one such term is allowed in the field.

Type an at(), rate() or cron() expression, pick a time zone, and this prints the next departures the way the documentation says Scheduler handles them, including daylight-saving skips and repeats. It runs in your browser and is a learning aid, not a validator: AWS has the final word.

Use a sandbox account and the AWS CLI v2. Every name below is a placeholder. This creates an SQS queue, an IAM role and a one-time schedule that drops a message in the queue and then deletes itself. It should fit well inside the free tiers.

1. A queue to receive the message.

   QUEUE_URL=$(aws sqs create-queue --queue-name sched-demo-queue \
     --query QueueUrl --output text)
   QUEUE_ARN=$(aws sqs get-queue-attributes --queue-url "$QUEUE_URL" \
     --attribute-names QueueArn --query Attributes.QueueArn --output text)

2. A role Scheduler can assume, allowed to send to that one queue.

   cat > trust.json <<'EOF'
   {"Version":"2012-10-17","Statement":[{"Effect":"Allow",
    "Principal":{"Service":"scheduler.amazonaws.com"},"Action":"sts:AssumeRole"}]}
   EOF
   ROLE_ARN=$(aws iam create-role --role-name sched-demo-role \
     --assume-role-policy-document file://trust.json --query Role.Arn --output text)
   
   cat > send.json <<EOF
   {"Version":"2012-10-17","Statement":[{"Effect":"Allow",
    "Action":"sqs:SendMessage","Resource":"$QUEUE_ARN"}]}
   EOF
   aws iam put-role-policy --role-name sched-demo-role \
     --policy-name sched-demo-send --policy-document file://send.json

3. A one-time schedule a few minutes from now. Change the at() time to just ahead of your local clock. If the call says the role cannot be assumed, wait a few seconds for IAM to catch up and run it again.

   aws scheduler create-schedule --name sched-demo-once \
     --schedule-expression "at(2026-11-12T15:00:00)" \
     --schedule-expression-timezone "America/Chicago" \
     --flexible-time-window '{"Mode":"OFF"}' \
     --action-after-completion DELETE \
     --target "{\"Arn\":\"$QUEUE_ARN\",\"RoleArn\":\"$ROLE_ARN\",\"Input\":\"hello from the timetable\"}"

4. After that minute passes, read the message.

   aws sqs receive-message --queue-url "$QUEUE_URL"
   aws scheduler list-schedules   # the one-time schedule should be gone

5. Clean up.

   # only needed if the schedule has not fired yet
   aws scheduler delete-schedule --name sched-demo-once
   aws iam delete-role-policy --role-name sched-demo-role --policy-name sched-demo-send
   aws iam delete-role --role-name sched-demo-role
   aws sqs delete-queue --queue-url "$QUEUE_URL"
   rm trust.json send.json