Getting an AMI ImageId with Node.js

In order to launch an Amazon EC2 instance, we need both the ImageId from the AMI we want to use and the SubnetId to launch the instance into.

In this article we illustrate how to get the ImageId from a Linux Amazon Machine Image (AMI) with Node.js. I have also included an additional example, which shows how we can sort the results to easily get the most recent AMI.

Let’s code!

// load AWS SDK
const AWS = require('aws-sdk');

// set the region to Oregon
AWS.config.update({region:'us-west-2'});

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

// get the current Amazon Linux 2 AMIs
const params = {
  Filters: [
    {
      Name: 'name',
      Values: [
        'amzn2-ami-hvm-2.0.????????-x86_64-gp2'
      ]
    },
    {
      Name: 'state',
      Values: [
        'available'
      ]
    },
  ],
  Owners: [
    'amazon',
  ]  
 };

ec2.describeImages(params, function(err, data) {
  if (err) {                      // an error occurred
    console.log(err, err.stack);  
  } else {                        // successful response
    console.log(data);
  }  
});

Example output:

data = {
  "Images": [
    {
      "Architecture": "x86_64",
      "CreationDate": "2019-01-14T19:17:25.000Z",
      "ImageId": "ami-032509850cf9ee54e",
      "ImageLocation": "amazon/amzn2-ami-hvm-2.0.20190115-x86_64-gp2",
      "ImageType": "machine",
      "Public": true,
      "OwnerId": "137112412989",
      "ProductCodes": [],
      "State": "available",
      "BlockDeviceMappings": [
       {
        "DeviceName": "/dev/xvda",
        "Ebs": {
         "DeleteOnTermination": true,
         "SnapshotId": "snap-04359c6bb66cf4243",
         "VolumeSize": 8,
         "VolumeType": "gp2",
         "Encrypted": false
        }
       }
      ],
      "Description": "Amazon Linux 2 AMI 2.0.20190115 x86_64 HVM gp2",
      "EnaSupport": true,
      "Hypervisor": "xen",
      "ImageOwnerAlias": "amazon",
      "Name": "amzn2-ami-hvm-2.0.20190115-x86_64-gp2",
      "RootDeviceName": "/dev/xvda",
      "RootDeviceType": "ebs",
      "SriovNetSupport": "simple",
      "Tags": [],
      "VirtualizationType": "hvm"
     }
  ]
}

From this output we want the ImageId, which we can easily obtain with a slight update to our callback function:

ec2.describeImages(params, function(err, data) {
  if (err) {                      // an error occurred
    console.log(err, err.stack);  
  } else {                        // successful response
    const imageId = data.Images[0].ImageId;
    console.log(imageId);         // ami-07669fc90e6e6cc47
  }  
});

Now that we have an AMI ImageId, let’s grab a SubnetId, and then launch an EC2 instance!

Bonus - Sorting AMIs by creation date

When we describe all the images available to us, the results are ordered arbitrarily. If we want to obtain the most recent AMI we can sort by CreationDate. In the following example, I have added a function sortByCreationDate that does just that.

// load AWS SDK
const AWS = require('aws-sdk');

// set the region to Oregon
AWS.config.update({region:'us-west-2'});

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

// get the current Amazon Linux 2 AMIs
const params = {
  Filters: [
    {
      Name: 'name',
      Values: [
        'amzn2-ami-hvm-2.0.????????-x86_64-gp2'
      ]
    },
    {
      Name: 'state',
      Values: [
        'available'
      ]
    },
  ],
  Owners: [
    'amazon',
  ]  
 };

// sorts the array of images by creation date
// the most recent AMIs will appear first
function sortByCreationDate(data) {
  const images = data.Images;
  images.sort(function(a,b) {
    const dateA = a['CreationDate'];
    const dateB = b['CreationDate'];
    if (dateA < dateB) {
      return -1;
    }
    if (dateA > dateB) {
      return 1;
    }
    // dates are equal
    return 0;
  });

  // arrange the images by date in descending order
  images.reverse();
}

ec2.describeImages(params, function(err, data) {
  if (err) {                      // an error occurred
    console.log(err, err.stack);  
  } else {                        // successful response
    sortByCreationDate(data);
    const imageId = data.Images[0].ImageId;
    console.log(imageId);         // ami-0cb72367e98845d43
  }  
});

As you can see in the above snippet, we obtain the ImageId in the exact same way as before, however the first element of the Images array will always be the most recent AMI! This is useful if we want to launch instances with the latest and greatest architecture.

Example output:

Bonus - Sorting AMIs by creation date

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