Why does my AWS Lambda script return 'Instances' instead of the instance ID?

Question

Below is my Lambda script which is a work in progress to back up some of my EC2 instances. I printed out the value of instanceId immediately after assignment and, to my surprise, it returned the string 'Instances' rather than an instance ID. I checked the expected format of the response here: http://boto3.readthedocs.io/en/latest/reference/services/ec2.html#EC2.Client.describe_instances and I believe I'm doing the call correctly. I first get just the Instances item from the list (schedule_instances = schedulers['Instances']) and then try to get the instance ID from that new list. Is this correct? I also have similar doubts about getting the VolumeId.

from __future__ import print_function
import json
import boto3
import datetime
import time

ec2 = boto3.client('ec2')

def lambda_handler(event, context):
    try:
        print("Creating snapshots on " + str(datetime.datetime.today()) + ".")
        schedulers = ec2.describe_instances(MaxResults=50, Filters=[{'Name':'tag:GL-sub-purpose', 'Values':['Schedule']}])
        print("Performing backup on " + str(len(schedulers)) + " schedules.")
        successful = []
        failed     = []
        schedule_instances = schedulers['Instances']
        for s in schedulers:
            try:
                instanceId=s['InstanceId']
                print (instanceId)
                snapshotDescription = instanceId + "-" + str(datetime.date.today().strftime('%Y-%m-%d')) + "-46130e7ac954-automated"
                ec2.create_snapshot(
                VolumeId=s['VolumeId'], 
                Description=snapshotDescription
                )
                successful.append(instanceId)
            except Exception as e:
                print(e)
                failed.append(instanceId + " :\t" + str(e))
        print("Performed backup on " + str(len(successful)) + " schedulers. Failed backup on " + str(len(failed)) + " schedulers. ")
        sendEmail(successful, failed)
        return "Success"
    except Exception as e:
        print(e)
        return "Failed"

Do you want to get the instance id of all instances that match the filter? There is a much simpler way to get this info. — helloV
– helloV, Commented Sep 12, 2016 at 16:55
My goal is to iterate through every instance in the list with the tag I've specified and create a snapshot for it. So I'll need the instance ID at that particular item each time the loop runs. — Rome_Leader
– Rome_Leader, Commented Sep 12, 2016 at 17:06

Ali · Accepted Answer · 2016-09-14 07:04:51Z

1

Looks like your for loop section isn't going through the Json Key values.

Use the following code for retrieving Instance-Ids using Boto3

import boto3

ec2 = boto3.client('ec2')

schedulers = ec2.describe_instances(InstanceIds=['i-xxxxxxxx'])

for i in schedulers['Reservations']:
   print i['Instances'][0]['InstanceId']

You can implement the for loop same in your code (If multiple instances are required use looping)

Hope this helps out.

answered Sep 14, 2016 at 7:04

Ali

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1 Comment

Rome_Leader Over a year ago

Ahh, this put me in the right direction. Had to parse the Reservation dictionary and then the resulting list of reservations first. Thanks for the help!

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