One of the most useful features of AWS is the ability to do pretty much everything from the provided CLI tools.  Even more usefully they are actually pretty easy to use!

For a number of reasons (including automating deployments, updating records based on dynamic IP addresses and creating internal hostnames for instance deployments) I wanted to be able to push updates to DNS zones hosted on AWS Route53, and I wanted to be able to script the process.  Below is an example of how acheive these updates from the CLI (in this instance updating an existing host record).

Assumptions:  You have installed and configured the AWS cli tools & the credentials you are using have the permissions necessary to make updates.  If you need any pointers with this you can find AWS’s documentation here.

Step 1 – Get the hosted zone ID

When you push a DNS update to Route53 you need to pass in the ID of the hosted zone (a hosted zone normally being the domain name you wish to update).  This command will list all of the zones / domains currently hosted under your account:

aws route53 list-hosted-zones

returning an output along the lines of:

{
    "HostedZones": [
        {
            "ResourceRecordSetCount": 4,
            "CallerReference": "C510CAC3-D5D9-XXXX-B039-1DFA2XXXXXXX",
            "Config": {},
            "Id": "/hostedzone/Z1W9BXXXXXXXLB",
            "Name": "oliverhelm.me."
        }
    ],
    "IsTruncated": false,
    "MaxItems": "100"
}

“Id”: “/hostedzone/Z1W9BXXXXXXXLB” is the bit you’re looking for with everthing after ‘/hostedzone/’ being the ID (in this instance Z1W9BXXXXXXXLB).

Step 2 – Building the change file

The changes are requested by building out a JSON file which is then sent to AWS. The format of this file varies a little based on the type of record you wish to update (details of this can be found here). In this instance i’m updating the A record homerouter.oliverhelm.me with a new IP address.  Create a file (i’ve called it: change-resource-record-sets.json) and insert the below.

{
    "Comment": "Update record to reflect new IP address of home router",
    "Changes": [
        {
            "Action": "UPSERT",
            "ResourceRecordSet": {
                "Name": "homerouter.cunniffehelm.co.uk.",
                "Type": "A",
                "TTL": 300,
                "ResourceRecords": [
                    {
                        "Value": "4.4.4.4"
                    }
                ]
            }
        }
    ]
}

The action ‘UPSERT’ will update the record for homerouter.cunniffehelm.co.uk if it exists and it not will create it.

Hint: Using http://jsonlint.com/ to check the format of your JSON file saves a fair bit of faffing around.

Step 3 – Pushing the update to AWS

The update is then pushed to AWS with the following command, where ‘change-resource-record-sets.json’ is the name of the JSON file you saved above and ‘–hosted-zone-id’ is the ID you found in step one:

aws route53 change-resource-record-sets --hosted-zone-id Z1W9BXXXXXXXLB --change-batch file:///root/change-resource-record-sets.json

A JSON responce will be returned (making it easy to script the interaction) and should look something like the below.  In theory it might take a short while for the update to take effect but in my experience it seems to be pretty much instant.  The status should be ‘PENDING’ upon submission and will change to ‘INSYNC’ after the change has been applied.  Don’t forget though that you may not see the change reflected in DNS queries until the TTL has been reached.

{
    "ChangeInfo": {
       "Status": "PENDING",
       "Comment": "Update home IP Address",
       "SubmittedAt": "2015-08-16T11:54:24.907Z",
       "Id": "/change/C2JAIG0XXXXXXX"
    }
}

You can check the status of any submitted updates with the command:

aws route53 get-change --id C2JAIG0XXXXXXX

where ‘–id’ is the ID returned after the submission.  Further details on this here.