How do you set up dynamic cname records?

Question

The project I'm working on requires that we mask AWS EC2 host names with our own subdomains.

---

For example:

ec2-176-34-163-40.eu-west-1.compute.amazonaws.com would map to gf53ef.domain.com

and

ec2-123-31-124-60.eu-west-1.compute.amazonaws.com would map to sdfrh5.domain.com

---

There will always be list available that stores the relationship between the domains.

This list changes ALL THE TIME. Meaning in one minute we could have 100+ new ec2 instances started, and the next all could terminate.

I'm wondering how to set up our Ubuntu server to handle this case.

Thanks

Answer 1

I am dong something similar on an openstack cloud for instance DNS name updates (probably not as dynamically as your requirement ;-), basically we have a bind named instance that accept dynamic updates.

I used webmin to configure the remote control using RNDC, and the basic bind configuration.

and then generate a key for remote access, and distribute it to your control node;

dnssec-keygen -a hmac-md5 -b 128 -n HOST remote-key  

the zone-file ends up like this;

zone "mydomain.com" {
  type master;
  file "master/mydomain.com";
  allow-update { key "remote-key"; };
};

allow-update provides the permission to update the master zone, allow-notify is the slave zone equivalent.

and then you can do something like this (nsupdate from bind-utils) to update the records from a client, I've not tested a CNAME update, but it should look something like this;

cat <<EOF | nsupdate -d -k "$KEY"
server ns1.mynameserver.com
zone domain.com
update delete gf53ef.domain.com.
update add gf53ef.domain.com.   IN  CNAME   ec2-176-34-163-40.eu-west-1.compute.amazonaws.com.
send
EOF

(you might have to double check the format for the CNAME example...)

This seems to be the configuration reference docs for named;
http://www.zytrax.com/books/dns/ch7/xfer.html

Examples can be obtained from these tutorials;

http://www.centos.org/docs/5/html/Deployment_Guide-en-US/s1-bind-rndc.html
http://dag.wieers.com/howto/bits/bind-ddns.php
http://linux.yyz.us/nsupdate/
http://www.semicomplete.com/articles/dynamic-dns-with-dhcp/

Answer 2

Thanks @CS3

Our solution is Route53 for now.

Here's how we set it up (PHP). We used this library: http://www.orderingdisorder.com/aws/route-53/

private function getDomain() {
    $sub = "e-".substr(md5($this->instance->dnsName), 2, 4);
    $domain = $sub.".domain.com";

    $dnsRecords = $this->route53->listResourceRecordSets('/hostedzone/123');

    $exists = false;
    foreach($dnsRecords["ResourceRecordSets"] as $dnsRecord) {
        if($dnsRecord["Name"] == $domain."." 
            AND $dnsRecord["Type"] == "CNAME") {
                $exists = true;
                break;
            }
    }

    if(!$exists) {
        $change = $this->route53->prepareChange('CREATE', $domain.".", 'CNAME', 300, $this->instance->dnsName);
        $this->route53->changeResourceRecordSets('/hostedzone/123', $change);
    }

    return $domain;
}

private function removeDomain() {
    $change = $this->route53->prepareChange('DELETE', $this->domain.".", 'CNAME', 300, $this->instance->dnsName);
    $this->route53->changeResourceRecordSets('/hostedzone/123', $change);
    $this->domain = null;
}