Python 3.6 AWS Lambda function to create a hosts file from running EC2 instances and put it in a bucket

gistfile1.txt

import boto3
import json
import jmespath

s3 = boto3.resource('s3')
ec2 = boto3.resource('ec2')

# creates a hosts file for all running ec2 instances
# you can add alias hostnames by adding a tag "hostname" to the EC2 instance

ec2_instances = []
region = 'eu-west-1'
hosts_file = ""
bucket_name = 'yourbucketname'

def lambda_handler(event, context):
    # create filter for instances in running state (unused)
    """
    filters = [
        {
            'Name': 'instance-state-name',
            'Values': ['running']
        }
    ]
    """
    filters = []
    hosts = \
"""
# this is an autogenerated hosts file that includes running EC2 instances
127.0.0.1 localhost

# The following lines are desirable for IPv6 capable hosts
::1 ip6-localhost ip6-loopback
fe00::0 ip6-localnet
ff00::0 ip6-mcastprefix
ff02::1 ip6-allnodes
ff02::2 ip6-allrouters
ff02::3 ip6-allhosts

# running EC2 instances:
"""

    # filter the instances based on filters() above (unused)
    instances = ec2.instances.filter(Filters=filters)

    for instance in instances:
        if instance.state.get("Name", None) != "running":
            continue
        tags = instance.tags or []
        line = instance.private_ip_address
        line = line.ljust(25, ' ')
        line += instance.private_dns_name
        for item in tags:
            if item.get("Key", None) == "hostname":
                hostname = item.get("Value", "")
                line += f" {hostname}"
        line += "\n"
        hosts += line

        # unused
        state_map = {
            0: 'pending',
            16: 'running',
            32: 'shutting-down',
            48: 'terminated',
            64: 'stopping',
            80: 'stopped',
        }

        ec2_instances.append(
            {
                'id': instance.id or "",
                'private_dns_name': instance.private_dns_name or "",
                'private_ip_address': instance.private_ip_address or "",
                'public_dns_name': instance.public_dns_name or "",
                'public_ip_address': instance.public_ip_address or "",
                'state': instance.state or "",
                'subnet_id': instance.subnet_id or "",
                'tags': tags or "",
                'vpc_id': instance.vpc_id or "",
            }
        )

    s3.Bucket(bucket_name).put_object(
        Key=f'{region}_ec2_instances.json',
        Body=bytes(json.dumps(ec2_instances, indent=4), encoding="UTF-8"),
        ContentType='application/json',
    )

    s3.Bucket(bucket_name).put_object(
        Key=f'{region}_hosts',
        Body=bytes(hosts, encoding="UTF-8"),
        ContentType='text/plain',
    )