Extracting data from nested object with AWS ec2.describeInstances in node.js

Question

I am relatively new to JavaScript.

I am trying to extract specific information from AWS about my EC2 instances using describeInstances. Specifically, I want to be able to provide a list of InstanceIds and extract from the resulting object the value of the Tags with Key: "Name". Here is the base code:

// Load the SDK for JavaScript
var AWS = require('aws-sdk');

// Load credentials and set region from JSON file
AWS.config.loadFromPath('./.aws/config.json');

// Create EC2 service object
var ec2 = new AWS.EC2({apiVersion: '2016-11-15'});

var params = {
  DryRun: false,
  InstanceIds: ['i-0be50217a4028a044', 'i-08b83c1c428e9a1d2']
};

ec2.describeInstances(params, function(err, data) {
  if (err) {
    console.log("Error", err.stack);
  } else {
    console.log("Success", JSON.stringify(data));
  }
});

Upon running this code, a large, hairy, and nested object is returned. The JSON.stringify() version of this is shown here:

{
    "Reservations": [{
        "ReservationId": "r-04e32387e546387ba",
        "OwnerId": "543800113692",
        "Groups": [],
        "Instances": [{
            "InstanceId": "i-08b83c1c428e9a1d2",
            "ImageId": "ami-8aa998ea",
            "State": {
                "Code": 16,
                "Name": "running"
            },
            "PrivateDnsName": "ip-10-77-113-210.us-west-2.compute.internal",
            "PublicDnsName": "ec2-35-165-200-222.us-west-2.compute.amazonaws.com",
            "StateTransitionReason": "",
            "KeyName": "Security1",
            "AmiLaunchIndex": 0,
            "ProductCodes": [],
            "InstanceType": "t2.micro",
            "LaunchTime": "2017-02-14T14:59:11.000Z",
            "Placement": {
                "AvailabilityZone": "us-west-2b",
                "GroupName": "",
                "Tenancy": "default"
            },
            "Monitoring": {
                "State": "disabled"
            },
            "SubnetId": "subnet-228da755",
            "VpcId": "vpc-af0f0dca",
            "PrivateIpAddress": "10.77.113.210",
            "PublicIpAddress": "35.165.200.222",
            "Architecture": "x86_64",
            "RootDeviceType": "ebs",
            "RootDeviceName": "/dev/sda1",
            "BlockDeviceMappings": [{
                "DeviceName": "/dev/sda1",
                "Ebs": {
                    "VolumeId": "vol-00e55d6bf114bfcaa0",
                    "Status": "attached",
                    "AttachTime": "2017-02-09T15:37:34.000Z",
                    "DeleteOnTermination": true
                }
            }],
            "VirtualizationType": "hvm",
            "ClientToken": "vOiiS1486654656072",
            "Tags": [{
                "Key": "Name",
                "Value": "Fenris"
            }],
            "SecurityGroups": [{
                "GroupName": "launch-wizard-2",
                "GroupId": "sg-2312072c"
            }],
            "SourceDestCheck": true,
            "Hypervisor": "xen",
            "EbsOptimized": false
        }]
    }, {
        "ReservationId": "r-0bbcb12e5c1162c23",
        "OwnerId": "543800113692",
        "Groups": [],
        "Instances": [{
            "InstanceId": "i-0be50217a40028a044",
            "ImageId": "ami-8ba011ea",
            "State": {
                "Code": 80,
                "Name": "stopped"
            },
            "PrivateDnsName": "ip-10-77-118-17.us-west-2.compute.internal",
            "PublicDnsName": "",
            "StateTransitionReason": "User initiated (2016-12-05 16:49:45 GMT)",
            "KeyName": "Security3",
            "AmiLaunchIndex": 0,
            "ProductCodes": [],
            "InstanceType": "t2.medium",
            "LaunchTime": "2016-12-02T15:50:08.000Z",
            "Placement": {
                "AvailabilityZone": "us-west-2b",
                "GroupName": "",
                "Tenancy": "default"
            },
            "Monitoring": {
                "State": "disabled"
            },
            "SubnetId": "subnet-228da700",
            "VpcId": "vpc-af0f1ccb",
            "PrivateIpAddress": "10.77.118.17",
            "StateReason": {
                "Code": "Client.UserInitiatedShutdown",
                "Message": "Client.UserInitiatedShutdown: User initiated shutdown"
            },
            "Architecture": "x86_64",
            "RootDeviceType": "ebs",
            "RootDeviceName": "/dev/sda1",
            "BlockDeviceMappings": [{
                "DeviceName": "/dev/sda1",
                "Ebs": {
                    "VolumeId": "vol-1c211ac8",
                    "Status": "attached",
                    "AttachTime": "2016-11-22T01:54:52.000Z",
                    "DeleteOnTermination": true
                }
            }],
            "VirtualizationType": "hvm",
            "ClientToken": "RQbhg1479762230132",
            "Tags": [{
                "Key": "Name",
                "Value": "Heimdall"
            }, {
                "Key": "Type",
                "Value": "Product Dev"
            }],
            "SecurityGroups": [{
                "GroupName": "LinuxAPIdev",
                "GroupId": "sg-5ea11777"
            }],
            "SourceDestCheck": true,
            "Hypervisor": "xen",
            "EbsOptimized": false
        }]
    }]
}

This is way more info than I need or want. I want to find a way to get only the values of Reservations.Instances.Tags.Value from the Reservations.Instances.Tags.Name key.

I thought that just writing it that way would work. But strangely, I can't seem to access the Reservations.Instances object at all:

// Load the SDK for JavaScript
var AWS = require('aws-sdk');

// Load credentials and set region from JSON file
AWS.config.loadFromPath('./.aws/config.json');

// Create EC2 service object
var ec2 = new AWS.EC2({apiVersion: '2016-11-15'});

var params = {
  DryRun: false,
  InstanceIds: ['i-0be5987a41191a044', 'i-08b83c3fc28e9a1d2']
};

// call EC2 to retrieve policy for selected bucket
ec2.describeInstances(params, function(err, data) {
  if (err) {
    console.log("Error", err.stack);
  } else {
    console.log("Success", JSON.stringify(data.Reservations.Instances));
  }
});

This results in:

Success undefined

What am I doing wrong? How do I access the lower level of data within Instances? It is obviously there... it shows up in JSON.stringify(), but clearly I don't have the right protocol for extracting it.

(P.S. Because of AWS credentials, you won't be able to run my code without minor changes. You'll need to reference your own credentials, and InstanceIds from your own EC2 instances.)

Abdennour TOUMI · Accepted Answer · 2017-02-14 19:43:55Z

3

Reservations, Instances and Tags All are arrays that''s why :

Reservations[0].Instances[0].Tags[0].Value
// value of 1ˢᵗ tag of 1ˢᵗ instance of 1ˢᵗ reservation

and Not

Reservations.Instances.Tags.Value

edited Feb 14, 2017 at 19:43

answered Feb 14, 2017 at 19:34

Abdennour TOUMI

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2 Comments

rucker Over a year ago

Whaddaya know. Works perfectly. Thank you.

Abdennour TOUMI Over a year ago

Your are Welcome 👋 👋

Yogesh Mistry · Accepted Answer · 2017-02-14 20:23:12Z

1

Within your describeInstances() method, you can simply use

// for InstanceId : "i-08b83c1c428e9a1d2"
data.Reservations[0].Instances[0].Tags[0].Value;
// and for InstanceId : "i-0be50217a40028a044"
data.Reservations[1].Instances[0].Tags[0].Value;

You can anyway create a function, if required, to return the tags value if the object structure is known.

answered Feb 14, 2017 at 20:23

Yogesh Mistry

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