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 schedule using cron expression.

1
AWSTemplateFormatVersion: '2010-09-09'
2
Description: EC2 scheduler
3

4
Parameters:
5
  Prefix:
6
    Type: String
7
    Default: ec2-scheduler
8
  InstanceIds:
9
    Type: String
10
    Description: '"i-1234567890abcdefg", "..."'
11
  ScheduleStartExpression:
12
    Type: String
13
    Default: 'cron(0 7 * * ? *)'
14
  ScheduleStopExpression:
15
    Type: String
16
    Default: 'cron(0 22 * * ? *)'
17
  ScheduleTimezone:
18
    Type: String
19
    Description: IANA timezone identifier. For the full list, refer to https://en.wikipedia.org/wiki/List_of_tz_database_time_zones
20
    Default: UTC
21
    AllowedValues:
22
      - UTC
23
      - Japan
24

25
Resources:
26
  ScheduleStart:
27
    Type: AWS::Scheduler::Schedule
28
    Properties:
29
      Name: !Sub ${Prefix}-schedule-start
30
      ScheduleExpression: !Ref ScheduleStartExpression
31
      ScheduleExpressionTimezone: !Ref ScheduleTimezone
32
      FlexibleTimeWindow:
33
        Mode: 'OFF'
34
      State: ENABLED
35
      Target:
36
        Arn: arn:aws:scheduler:::aws-sdk:ec2:startInstances
37
        Input: !Sub |-
38
          {
39
            "InstanceIds": [${InstanceIds}]
40
          }
41
        RoleArn: !GetAtt Role.Arn
42

43
  ScheduleStop:
44
    Type: AWS::Scheduler::Schedule
45
    Properties:
46
      Name: !Sub ${Prefix}-schedule-stop
47
      ScheduleExpression: !Ref ScheduleStopExpression
48
      ScheduleExpressionTimezone: !Ref ScheduleTimezone
49
      FlexibleTimeWindow:
50
        Mode: 'OFF'
51
      State: ENABLED
52
      Target:
53
        Arn: arn:aws:scheduler:::aws-sdk:ec2:stopInstances
54
        Input: !Sub |-
55
          {
56
            "InstanceIds": [${InstanceIds}]
57
          }
58
        RoleArn: !GetAtt Role.Arn
59

60
  Role:
61
    Type: AWS::IAM::Role
62
    Properties:
63
      RoleName: !Sub ${Prefix}-role
64
      AssumeRolePolicyDocument:
65
        Version: 2012-10-17
66
        Statement:
67
          - Effect: Allow
68
            Principal:
69
              Service:
70
                - scheduler.amazonaws.com
71
            Action:
72
              - sts:AssumeRole
73
      Policies:
74
        - PolicyName: ec2
75
          PolicyDocument:
76
            Version: 2012-10-17
77
            Statement:
78
              - Effect: Allow
79
                Action:
80
                  - ec2:StartInstances
81
                  - ec2:StopInstances
82
                Resource: !Sub arn:aws:ec2:${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

The provisioned EventBridge Scheduler will automatically start the EC2 instance at 7:00 AM and stop it at 10:00 PM.

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

Setting up two EventBridge Schedules with cron expressions got an EC2 instance starting at 7 AM and stopping at 10 PM automatically. 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.

Back to posts