Comments on: Adding EC2 instances to Route53

By: Ian B

Ian B — Thu, 24 Jan 2013 16:21:00 +0000

That’s a good point. If you want it to return all the records and have the client pick, you’ll definitely need an A record.

The latency-weighted stuff is pretty cool for geographical load balancing, too.

By: lgibelli

lgibelli — Wed, 23 Jan 2013 21:23:00 +0000

Just a word of advice: I was fooled into thinking that the script doesn’t work because when resolving a weighted round robin, Route53 only returns one CNAME (in rotation), not the whole set.
So don’t be surprised if you start N instances and when you try to resolve the round robin you get only 1 IP address at a time.
If you want to have all the IPs in a single record you have to use an A record.

By: Ian B

Ian B — Wed, 23 Jan 2013 20:34:00 +0000

That’s partly why Route53 does Aliases. When doing a round-robin, you need to make it weighted.

By: lgibelli

lgibelli — Wed, 23 Jan 2013 16:59:00 +0000

A Round robin of CNAMEs is illegal according to rfc2181:
“[...] That is, for any label in the DNS (any domain name)
exactly one of the following is true:
+ one CNAME record exists, optionally accompanied by SIG, NXT, and
KEY RRs, [...]”

I just tried to create a round robin of CNAMEs on Route53 and got the expected response:

“RRSet of type CNAME with DNS name testcname.mydomain. does not contain exactly one resource record.”

Either use a RR of IP addresses or do a weighted round robin of CNAMEs, all with the same weight (see http://docs.amazonwebservices.com/Route53/latest/DeveloperGuide/WeightedResourceRecordSets.html for more info on Weighted records).

Your script tried to create a “simple” (i.e. regular) round robin and therefore it fails.
I just replaced “CNAME” with “A” at line 77 and public-hostname with public-ipv4 at line 27 to make it work.

By: Ian B

Ian B — Wed, 23 Jan 2013 16:18:00 +0000

Is that a recent change to the API? Because when I wrote this, it had no problem creating CNAMEs. That’s the Best Practice for anything within Amazon’s cloud, as communication between the boxes resolves to the internal IP address when using the CNAME.

Cloudfront also requires the use of CNAMEs or Aliases (internal to Route53).

By: lgibelli

lgibelli — Wed, 23 Jan 2013 14:55:00 +0000

At line 77 you try to create a RR of CNAMEs. Is that right? You can’t do that. You can only create RR of MX, NS and A records, not CNAMEs.

By: Add EC2 to Route53 « 0ddn1x: tricks with *nix

Add EC2 to Route53 « 0ddn1x: tricks with *nix — Tue, 30 Oct 2012 18:28:10 +0000

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By: Adding EC2 instances to Route53 | Pinehead.tv

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By: Ian B

Ian B — Mon, 24 Sep 2012 12:18:00 +0000

correct – you could do this with an external monitor that checks for ping and service availability once a server is up, and removes the server if it goes down.

By: Zac

Zac — Mon, 24 Sep 2012 07:23:00 +0000

If I understand this correctly, this script will add the server to Route 53 when it starts up, and remove on a shutdown, but how do you handle the case where a server crashes (or otherwise does not shutdown gracefully), you would really still want to remove it from the weighted round robin, otherwise requests will still resolve to the offline server.