Python script to update /etc/hosts and iTerm dynamic profiles with the list of aws instances

update-aws-hosts.py

#!/usr/local/bin/python
# coding: UTF-8

import boto3
import json

# Main function that runs the whole thing
def updateAll():
    instances,groups = getEC2Instances()
    updateHosts(instances,groups)
    updateTerm(instances,groups)

# Outputs to stdout the list of instances and returns EC2 instances as an array of dictionaries containing the following fields:
# name          => Instance name formed by the instance class/group and the domain prefix (aws.)
# group         => Group associated with the instance (webapp, vpn, etc.)
# index         => Index of this instance in the group
def getEC2Instances():

    client = boto3.client('ec2')

    response = client.describe_instances(
            Filters = [{
                    'Name':'instance-state-name',
                    'Values': [
                            'running'
                    ]
                    }
            ]
    )

    groups = {}
    instances = {}

    for reservation in response['Reservations']:
            for instance in reservation['Instances']:
                    for tag in instance['Tags']:
                            if tag['Key'] == 'Name':
                                    name = tag['Value']
                                    break
                    ip = instance['NetworkInterfaces'][0]['PrivateIpAddress']
        
                    if name in groups:
                        groups[name] = groups[name] + 1
                    else:
                        groups[name] = 1

                    instances[ip] = {'name':'aws.' + name,'index':groups[name],'group':name}
                    print ip + "\t" + 'aws.' + name + str(groups[name])
   
    for ip in instances:
        instance = instances[ip]
        instance['name'] = instance['name'] + str(instance['index']) if groups[instance['group']] > 1 else instance['name']

    return instances, groups

# Updates the /etc/hosts file with the EC2 private addresses
# /etc/hosts must include the list of EC2 instances between two lines: the first contains '# AWS EC2' 
# and the last a single # character.
def updateHosts(instances,groups):
    handle = open('/etc/hosts')
    lines = handle.read().splitlines()    
    handle.close()
    state = False

    hout = open('/etc/hosts','wt')

    startDelimiter = "# AWS EC2"
    endDelimiter = "#"

    for line in lines:
        if line == startDelimiter:
            state = True
            continue
        if state == True and line == endDelimiter:
            state = False
            continue
        if not state:
            hout.write(line + "\n")

    hout.write(startDelimiter + "\n")
    for ip in instances:
        instance = instances[ip]
        name = instance['name']
        hout.write(ip + "\t" + name + "\n")
	
    hout.write(endDelimiter + "\n")
    hout.close()

def updateTerm(instances,groups):
    handle = open('/Users/gmartin/Library/Application Support/iTerm2/DynamicProfiles/aws','wt')
    state = False

    profiles = []

    for instance in instances:
        shortName = instances[instance]['name'][4:]
        group = instances[instance]['group']
        tags =["AWS",group] if groups[group] > 1 else ['AWS']
        name = instances[instance]['name']

        profile = {"Name":name,
                    "Guid":name,
                    "Badge Text":shortName,
                    "Tags":tags,
                    "Dynamic Profile Parent Name": "Bastión AWS",
                    "Custom Command" : "Yes",
                    "Command" : "ssh -oStrictHostKeyChecking=no -oUpdateHostKeys=yes "+name}

        profiles.append(profile)

    profiles = {"Profiles":sorted(profiles)} 
    handle.write(json.dumps(profiles,sort_keys=True,indent=4, separators=(',', ': ')))
    handle.close()

updateAll()