Support ELB failover via Route53 Alias

[codefromthecrypt]

At Netflix, we'd like to target edge traffic to region-specific Route53 A, AAAA Aliases as opposed to dualstack CNAMEs.

An example CLI command would be the following:

Ex.

$ denominator -n route53 record -z myzone.com. add -t A -n foo.myzone.com. --elb-dnsname abadmin-795710131.us-east-1.elb.amazonaws.com
;; in zone myzone.com. adding to rrset foo.myzone.com. A values: [{HostedZoneId=Z3DZXE0Q79N41H, DNSName=abadmin-795710131.us-east-1.elb.amazonaws.com}]
[Route53#listHostedZones] ---> GET https://route53.amazonaws.com/2012-12-12/hostedzone HTTP/1.1
[Route53#listHostedZones] <--- HTTP/1.1 200 OK (623ms)
[Route53#listResourceRecordSets] ---> GET https://route53.amazonaws.com/2012-12-12/hostedzone/Z3I0BTR7N27QRM/rrset?name=foo.myzone.com.&type=A HTTP/1.1
[Route53#listResourceRecordSets] <--- HTTP/1.1 200 OK (161ms)
[Route53#listResourceRecordSets] ---> GET https://route53.amazonaws.com/2012-12-12/hostedzone/Z3I0BTR7N27QRM/rrset?name=foo.myzone.com.&type=A HTTP/1.1
[Route53#listResourceRecordSets] <--- HTTP/1.1 200 OK (146ms)
[Route53#changeResourceRecordSets] ---> POST https://route53.amazonaws.com/2012-12-12/hostedzone/Z3I0BTR7N27QRM/rrset HTTP/1.1
[Route53#changeResourceRecordSets] <--- HTTP/1.1 200 OK (152ms)
;; ok

denominator could maintain a lookup table for the default elb hosted zone ids, similar to how it is done in fog.

[codefromthecrypt]

Here's the current ELB region mappings:

ELB Region	HostedZoneId
us-east-1	Z3DZXE0Q79N41H
us-west-2	Z33MTJ483KN6FU
eu-west-1	Z3NF1Z3NOM5OY2
ap-northeast-1	Z2YN17T5R711GT
ap-southeast-1	Z1WI8VXHPB1R38
sa-east-1	Z2ES78Y61JGQKS

[codefromthecrypt]

cc @colmmacc @allenxwang @coryb

[codefromthecrypt]

In the denominator model, there's 2 ways to approach this.

• make a new Route53-specific RData type of Alias which contains 2 fields: HostedZoneId and DNSName
• subclass ResourceRecordSet in route53, adding an alias() optional field.

The special rdata type seems least intrusive, but could result in confusion as record sets with type A or AAAA typically always have rdata with one field: address. If we change this, some tools could possibly break as they'd get null asking for: address. OTOH, if we choose to add a field for the alias target, there'd be no rdata elements, which would break folks in the same way.

I prefer just making a route53-specific Alias rdata type.

[codefromthecrypt]

whoops.. I meant @q

[codefromthecrypt]

In the base route53 denominator tests, we can alias another route53 record to ensure base functionality works. The ELB region mapping table can be scoped to the CLI and mock tested there.

[codefromthecrypt]

issue #245 closes this, and will be merged shortly.