Working with JSON output from AWSCLI

Posted under others On By xpk

The program looks short but the way Python handles JSON is not very elegant. JSON is supposed to be a serialized object, so it should be processed as an object. But here, it’s processed as an array.

import json
import sys

print "Usage: cat JSON | | column -t"
jsonInput = sys.stdin
awsObject = json.load(jsonInput)

instances = awsObject[‘Reservations’]

for instance in instances:
print instance[‘Instances’][0][‘Tags’][0][‘Value’], instance[‘Instances’][0][‘InstanceId’], instance[‘Instances’][0][‘PublicDnsName’]

Not only that, there is no type definition with any of the variables. I have no idea what was returned by json.load.

Also, exception handling is quite poor. I tried to do a try-except block but the program got stuck with no stdin was piped. If I try to read from stdin and calculate the length, the read line is consumed and I couldn’t go back.

Anyway, this program will take output from awscli (json format) and extract 3 fields that I want.

On a relevant note, it is also possible to use the –query option to narrow down the search fields. For example

$ aws ec2 describe-volumes --output=text --query 'Volumes[*].{ID:VolumeId,Size:Size}'
vol-d74xxx93	30
vol-784xxx3c	30
vol-854xxxc1	60


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