Lambda function written in Python which when triggered starts or stops the EC2 instances.

start_ec2_instances.py

import boto3

ec2 = boto3.resource('ec2', 'us-east-1')

def lambda_handler(event, context):
 instances = ec2.instances.filter(Filters=[{'Name': 'instance-state-name', 'Values': ['stopped']},{'Name': 'tag:AutoStop','Values':['true']}])
 for instance in instances:
     id=instance.id
     ec2.instances.filter(InstanceIds=[id]).start()
     print("Instance ID is started:- "+instance.id)
 return "success"

stop_ec2_instances.py

import boto3

ec2 = boto3.resource('ec2', 'us-east-1')

def lambda_handler(event, context):
 instances = ec2.instances.filter(Filters=[{'Name': 'instance-state-name', 'Values': ['running']},{'Name': 'tag:AutoStop','Values':['true']}])
 for instance in instances:
     id=instance.id
     ec2.instances.filter(InstanceIds=[id]).stop()
     print("Instance ID is stopped:- "+instance.id)
 return "success"

NOTE: All the EC2 instances which you need to start or stop must contain the tag AutoStop = true

To view the complete terraform code, click here.