AWS EventBridge Scheduler: Starting and Stopping EC2 on a Schedule

Starting and stopping EC2 instances on a cron schedule with EventBridge Scheduler calling the EC2 API directly, no Lambda involved.

Takahiro Iwasa

2024-06-15

3 min read

EventBridge Scheduler can start and stop EC2 instances on a cron schedule without any Lambda function in between.

Building

Start an EC2 instance for the test.

aws ec2 run-instances \
  --image-id ami-0f9fe1d9214628296 \
  --count 1 \
  --instance-type t2.micro \
  --security-group-ids <SECURITY_GROUP_IDS> \
  --subnet-id <SUBNET_ID>

The ScheduleStartExpression and ScheduleStopExpression parameters on lines 11-16 define the schedules as cron expressions.

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AWSTemplateFormatVersion: '2010-09-09'
2
Description: EC2 scheduler
3

4
Parameters:
5
  Prefix:
6
    Type: String
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    Default: ec2-scheduler
8
  InstanceIds:
9
    Type: String
10
    Description: '"i-1234567890abcdefg", "..."'
11
  ScheduleStartExpression:
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    Type: String
13
    Default: 'cron(0 7 * * ? *)'
14
  ScheduleStopExpression:
15
    Type: String
16
    Default: 'cron(0 22 * * ? *)'
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  ScheduleTimezone:
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    Type: String
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    Description: IANA timezone identifier. For the full list, refer to https://en.wikipedia.org/wiki/List_of_tz_database_time_zones
20
    Default: UTC
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    AllowedValues:
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      - UTC
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      - Japan
24

25
Resources:
26
  ScheduleStart:
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    Type: AWS::Scheduler::Schedule
28
    Properties:
29
      Name: !Sub ${Prefix}-schedule-start
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      ScheduleExpression: !Ref ScheduleStartExpression
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      ScheduleExpressionTimezone: !Ref ScheduleTimezone
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      FlexibleTimeWindow:
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        Mode: 'OFF'
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      State: ENABLED
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      Target:
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        Arn: arn:aws:scheduler:::aws-sdk:ec2:startInstances
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        Input: !Sub |-
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          {
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            "InstanceIds": [${InstanceIds}]
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          }
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        RoleArn: !GetAtt Role.Arn
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  ScheduleStop:
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    Type: AWS::Scheduler::Schedule
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    Properties:
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      Name: !Sub ${Prefix}-schedule-stop
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      ScheduleExpression: !Ref ScheduleStopExpression
48
      ScheduleExpressionTimezone: !Ref ScheduleTimezone
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      FlexibleTimeWindow:
50
        Mode: 'OFF'
51
      State: ENABLED
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      Target:
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        Arn: arn:aws:scheduler:::aws-sdk:ec2:stopInstances
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        Input: !Sub |-
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          {
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            "InstanceIds": [${InstanceIds}]
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          }
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        RoleArn: !GetAtt Role.Arn
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  Role:
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    Type: AWS::IAM::Role
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    Properties:
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      RoleName: !Sub ${Prefix}-role
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      AssumeRolePolicyDocument:
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        Version: 2012-10-17
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        Statement:
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          - Effect: Allow
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            Principal:
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              Service:
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                - scheduler.amazonaws.com
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            Action:
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              - sts:AssumeRole
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      Policies:
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        - PolicyName: ec2
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          PolicyDocument:
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            Version: 2012-10-17
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            Statement:
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              - Effect: Allow
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                Action:
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                  - ec2:StartInstances
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                  - ec2:StopInstances
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                Resource: !Sub arn:aws:ec2:${AWS::Region}:${AWS::AccountId}:instance/i-*

Deploy the CloudFormation stack with the following command:

aws cloudformation deploy \
  --template-file ./template.yaml \
  --stack-name ec2-scheduler \
  --parameter-overrides InstanceIds='"<INSTANCE_ID1>", "<INSTANCE_ID2>"' \
  --capabilities CAPABILITY_NAMED_IAM

Testing

With the default UTC timezone in this template, EventBridge Scheduler starts the EC2 instance at 07:00 UTC and stops it at 22:00 UTC.

Cleaning Up

Clean up all the AWS resources provisioned during this example with the following command:

aws ec2 terminate-instances --instance-ids <INSTANCE_IDS>
aws cloudformation delete-stack --stack-name ec2-scheduler

Conclusion

Two EventBridge Scheduler schedules start the EC2 instance at 07:00 and stop it at 22:00 in the timezone selected by ScheduleExpressionTimezone.

Targeting the EC2 API directly through arn:aws:scheduler:::aws-sdk:ec2:startInstances is what keeps this setup free of any Lambda function — EventBridge Scheduler can call the AWS SDK directly, so the schedule and the IAM role granting ec2:StartInstances/ec2:StopInstances are the entire solution.

The one setting worth double-checking before relying on this for cost savings is ScheduleExpressionTimezone: since it defaults to UTC in the template, a schedule meant to align with business hours in another timezone needs that parameter set explicitly, or instances will start and stop several hours off from what’s expected.

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