Boto3 - Automate Scheduling of EC2 Instances: Using Lambda and Cron

Managing the aws cost and availability of your ec2 instances can be challenging if they run all the time without any need. For example, many teams / companies often have development instances that are not used after working hours and weekends. So, by shutting these down when not in use, you could save a significant amount on your AWS bill.

In our case, we tag all development instances (or any other resources that don’t need to run outside working hours) with env: dev. This makes it easy to filter and manage these instances separately from production or other critical workloads.

In this post, we’ll walk you through how to automate the process of stopping and starting these tagged instances using two approaches:

1. Using AWS Lambda.
2. Using an on-premises machine with Cron.

Both methods will utilize Boto3, the AWS SDK for Python.

---

Prerequisites

Before starting, ensure you:

• Have Python installed (for on-prem).

• Install Boto3 using:

    pip install boto3 
  

• Set up AWS credentials using aws configure or environment variables.
• Grant your IAM role or user sufficient permissions:
  • ec2:DescribeInstances
  • ec2:StopInstances
  • ec2:StartInstances

---

Approach 1: Using AWS Lambda to Schedule EC2 Instances

AWS Lambda, combined with Amazon EventBridge (CloudWatch Events), can automate the start and stop of EC2 instances.

1.1: Lambda Script to Stop EC2 Instances

This Lambda script stops EC2 instances with the tag env=dev in the regions ex. us-east-1, us-east-2 , us-west-1 and us-west-2 if they are running.

import boto3
import json

def lambda_handler(event, context):
    ### HERE, set your regions in this list
    regions = ['us-east-1', 'us-east-2','us-west-1', 'us-west-2']
    for region_name in regions:
        print(f"Checking region: {region_name}")
        ec2_resource = boto3.resource('ec2', region_name=region_name)
				
     ### Filter only running instances with Tag env=dev
        filters = [
            {'Name': 'instance-state-name', 'Values': ['running']},  
            {'Name': 'tag:env', 'Values': ['dev']}                  
        ]

        instances = list(ec2_resource.instances.filter(Filters=filters))

        if instances:
            print(f"Instances in region {region_name}:")
            for instance in instances:
                print(f"Stopping Instance ID: {instance.id} State: {instance.state['Name']}")
                instance.stop()  
        else:
            print(f"No running 'dev' EC2 instances in region {region_name}")

    return {
        'statusCode': 200,
        'body': json.dumps('EC2 instances stopped successfully!')
    }

1.2: Lambda Script to Start EC2 Instances

This Lambda script will starts EC2 instances with the tag env=dev if they are stopped.

import boto3
import json

def lambda_handler(event, context):
    regions = ['us-east-1', 'us-east-2','us-west-1', 'us-west-2']
    for region_name in regions:
        print(f"Checking region: {region_name}")
        ec2_resource = boto3.resource('ec2', region_name=region_name)
        filters = [
            {'Name': 'instance-state-name', 'Values': ['stopped']},  
            {'Name': 'tag:env', 'Values': ['dev']}                  
        ]

        instances = list(ec2_resource.instances.filter(Filters=filters))
        if instances:
            print(f"Instances in region {region_name}:")
            for instance in instances:
                print(f"Starting Instance ID: {instance.id}")
                instance.start()  
        else:
            print(f"No stopped 'dev' EC2 instances in region {region_name}")

    return {
        'statusCode': 200,
        'body': json.dumps('EC2 instances started successfully!')
    }

Timeouts Troubleshooting Note:

When you run AWS Lambda you might face timeout error.

So, it’s important to configure the timeout to ensure the function has enough time (ex. 30 seconds) to complete its task. The default timeout is 3 seconds, which might not be sufficient for scripts that need to iterate over multiple regions/instances.

1.3: Scheduling with EventBridge

1. Go to the EventBridge Console in AWS.
2. Create a new rule:
   • Name your rule - ex: stop-ec2-dev-instances
   • And schedule expression:
     • Stop at 6 PM: cron(0 18 ? * MON-FRI *)
     • Start at 6 AM: cron(0 6 ? * MON-FRI *)
3. Set the target as your Lambda function.

---

Approach 2: Using Cron on an On-Premises Machine

If you prefer to manage this locally, use the following scripts and schedule them with cron.

2.1: Stopping EC2 Instances Script

import boto3

def list_used_ec2_instances():
    regions = ['us-east-1', 'us-east-2','us-west-1', 'us-west-2']
    for region_name in regions:
        print(f"Checking region: {region_name}")
        ec2_resource = boto3.resource('ec2', region_name=region_name)
        filters = [
            {'Name': 'instance-state-name', 'Values': ['running']},
            {'Name': 'tag:env', 'Values': ['dev']}
        ]

        instances = list(ec2_resource.instances.filter(Filters=filters))

        if instances:
            print(f"Instances in region {region_name}:")
            for instance in instances:
                print(f"Stopping Instance ID: {instance.id}")
                instance.stop()
        else:
            print(f"No running 'dev' EC2 instances in region {region_name}")

list_used_ec2_instances()

2.2: Starting EC2 Instances Script

import boto3

def list_used_ec2_instances():
    regions = ['us-east-1', 'us-east-2','us-west-1', 'us-west-2']
    for region_name in regions:
        print(f"Checking region: {region_name}")
        ec2_resource = boto3.resource('ec2', region_name=region_name)

        filters = [
            {'Name': 'instance-state-name', 'Values': ['stopped']},
            {'Name': 'tag:env', 'Values': ['dev']}
        ]

        instances = list(ec2_resource.instances.filter(Filters=filters))

        if instances:
            print(f"Instances in region {region_name}:")
            for instance in instances:
                print(f"Starting Instance ID: {instance.id}")
                instance.start()
        else:
            print(f"No stopped 'dev' EC2 instances in region {region_name}")

list_used_ec2_instances()

2.3: Schedule with Cron

1. Open the crontab editor:

    crontab -e
   

2. Add the following entries:

    0 18 * * 1-5 /usr/bin/python3 /scripts/stop_ec2.py
    0 6 * * 1-5 /usr/bin/python3 /scripts/start_ec2.py
   

   • 0 18: Runs the stop script at 6 PM, Monday to Friday.
   • 0 6: Runs the start script at 6 AM, Monday to Friday.