Dynroute53

Abstract

This small program updates an Amazon AWS Route53 A Record for the specified -domain attached to a specified -hostedZoneID with the external IP address exposed to the internet.

Use case

I built this to run on a Raspberry 🍓 PI and I scheduled it with a cron job to run every minute: the program creates a local cache on the filesystem and if the external IP is equal to the one stored in the dynroute.cache file it won't update Route53, otherwise it will call the Amazon service to update the A record.

This helps me to reach my Raspberry PI by using a domain name even if the connection gets reset as within at most one minute the domain will be reattached to the correct (new) IP address.

How to

To run this, you need:

• your AWS credentials stored in the (usual) ~/.aws/credentials file [more info]
• the user linked to those credentials needs to have access rights to the route53:ChangeResourceRecordSets action (see AWS policy example below)

AWS policy example

{
    "Version": "2012-10-17",
    "Statement": [
        {
            "Effect": "Allow",
            "Action": [
                "route53:ChangeResourceRecordSets"
            ],
            "Resource": [
                "arn:aws:route53:::hostedzone/%YOUR_HOSTED_ZONE%"
            ]
        }
    ]
}

The program requires two parameters:

• -domain: the entire subdomain/domain (excluding the protocol), for example myblog.mydomain.com
• -hostedZoneID: the AWS hosted zone ID as arn (in the policy example, replace %YOUR_HOSTED_ZONE% with it as well to allow the script to operate only on this specific zone/domain
• verbose: if false prints only errors and Route53 updates because of cache miss, not cache hits. Useful if you pipe the output to a log file (like I do). Defaulted to true.

This is what a call looks like:

./dynroute53 -domain=myblog.mydomain.com -hostedZoneID=Z123ABCDE45F67

This is what the crontab entry looks like if you want to run the check every minute:

* * * * * /home/user/dynroute53 -domain=myblog.mydomain.com -hostedZoneID=Z123ABCDE45F67 -verbose=false >> /home/user/logs/cron.log 2>&1

Build

If you want to build it for a Raspberry PI bear in mind I had an issue with the AWS Go SDK and I had to cross compile the program on my Mac with these env vars:

env GOOS=linux GOARCH=arm GOARM=7 go build main.go