Find First IP Address in VPC That Can Be Allocated

In this guide, we will review a JavaScript code snippet that uses AWS SDK to find the first available IP address in a VPC that can be allocated.

Code

Below is the code for finding the first available IP address in the scope of a specified Amazon VPC:

const AWS = require('aws-sdk');
const ec2 = new AWS.EC2({apiVersion: '2016-11-15'});

var params = {
  Filters: [
    {
      Name: "availability-zone",
      Values: [
        "us-west-2a"
      ]
    },
  ]
};
    
ec2.describeAddresses(params, function(err, data) {
  if (err) console.log(err, err.stack); // an error occurred
  
  else {
    for(let i = 0; i<=4; i++) {
      if(data.Addresses[i]) {
        console.log(`First available IP: ${data.Addresses[i].PublicIp}`);
        break;
      }
    }
  }                   
});

Detailed Code Explanation

The code starts by importing the AWS SDK and creating an EC2 service object using the current API version.

The params object is set to filter on the availability zone 'us-west-2a'. This could be updated to reflect the appropriate environment for the user.

This code then describes (finds) the Amazon Elastic IP addresses available for that specific region and then initiates a FOR loop to go through the first five IP addresses and find the first available IP address. If an error is encountered, it logs the error.

Expected Output

This code will log the first available IP address in the specified availability zone, returning it in the console. The output is a string and might look something like this:

First available IP: 52.32.25.18

Considerations & Caveats

1. Remember to replace "us-west-2a" with the appropriate availability zone based on your environment.
2. The AWS SDK used in this code snippet is not set ever to use an external configuration file or environment variables for loading AWS credentials. Please ensure that your SDK is appropriately configured.
3. The code doesn't handle all the edge cases for situations where there might be no available IP addresses.

Required IAM Permissions and Example Policy

A minimum IAM policy required for this script is:

{
    "Version": "2012-10-17",
    "Statement": [
        {
            "Sid": "EC2Permissions",
            "Effect": "Allow",
            "Action": "ec2:DescribeAddresses",
            "Resource": "*"
        }
    ]
}

This policy allows the describeAddresses action, which is required to retrieve information about the IP addresses.

FAQ

1. What happens if there are no available IP addresses?

If there is no available Elastic IP address, the script will log the error message received from AWS.

2. Does this script work with different AWS SDK versions?

The code uses EC2 API version '2016-11-15'. You should merely replace it with your required AWS SDK version.

3. How can I change the region for finding available IP addresses?

You can modify the availability zone in the params variable in the code.

4. Does this script handle AWS Credential Provider exceptions?

No, the script assumes that AWS credentials are correctly configured in your environment. If not, you might get a credentials-related error.