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
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

Ali Ali · Accepted Answer · 2016-09-14T07:04:51

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.

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

1 Answers