Accessing Nested JSON [AWS Metadata] with Python

Question

I'm using Lambda to run through my AWS account, returning a list of all instances. I need to be able to print out all of the 'VolumeId' values, but I can't work out how to access them as they are nested. I am able to print out the first VolumeId for each instance, however, some of the instances have several volumes, and some only have one. I think I know why I get these results, but I can't work out what to do to get all of them back.

Here's a snippet of what the JSON for one instance looks like:

{  
'Groups':[],
'Instances':[  
  {  
     'AmiLaunchIndex':0,
     'ImageId':'ami-0',
     'InstanceId':'i-0123',
     'InstanceType':'big',
     'KeyName':'nonprod',
     'LaunchTime':'date',
     'Monitoring':{  
        'State':'disabled'
     },
     'Placement':{  
        'AvailabilityZone':'world',
        'GroupName':'',
        'Tenancy':'default'
     },
     'PrivateDnsName':'secret',
     'PrivateIpAddress':'1.2.3.4',
     'ProductCodes':[  

     ],
     'PublicDnsName':'',
     'State':{  
        'Code':80,
        'Name':'stopped'
     },
     'StateTransitionReason':'User initiated',
     'SubnetId':'subnet-1',
     'VpcId':'vpc-1',
     'Architecture':'yes',            
     'BlockDeviceMappings':[  
        {  
           'DeviceName':'/sda',
           'Ebs':{  
              'AttachTime':'date',
              'DeleteOnTermination':True,
              'Status':'attached',
              'VolumeId':'vol-1'
           }
        },
        {  
           'DeviceName':'/sdb',
           'Ebs':{    
              'AttachTime':'date'),
              'DeleteOnTermination':False,
              'Status':'attached',
              'VolumeId':'vol-2'
           }
        }
     ],

This is what I'm doing to get the first VolumeId:

ec2client = boto3.client('ec2')
ec2 = ec2client.describe_instances()
for reservation in ec2["Reservations"]:
    for instance in reservation["Instances"]:
        instanceid = instance["InstanceId"]

        volumes = instance["BlockDeviceMappings"][0]["Ebs"]["VolumeId"]
        print("The associated volume IDs for this instance are: ",(volumes))

I think the reason that I'm getting just the first ID is because I'm referencing the first element within "BlockDeviceMappings", but I can't work out how to get the other ones. If I try it without specifying the [0], I get the list indices must be integers or slices, not str error. I tried to use a dictionary instead of a list too, but felt like I was barking up the wrong tree with that one. Any suggestions/help would be appreciated!

kmcodes · Accepted Answer · 2019-06-18 11:11:57Z

1

One possible answer, not particularly pythonic

...

id_list = []
volumes_data = instance["BlockDeviceMappings"]
for element in volumes_data:
    id_list.append(element["Ebs"]["VolumeId"])

Or else use json.loads and then iterate though json using .get syntax like the final answer in this

answered Jun 18, 2019 at 11:11

kmcodes

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1 Comment

Mcar49 Over a year ago

Perfect, that's all I needed. I did try doing it with json.load, json.loads, & json.dumps but struggled to do what I needed. Kept getting that same list indices error. Thanks for the solution!

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