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dnscontrol/docs/alias.md
Brice Figureau 7b8d608019 ROUTE53: Support Route53's ALIAS record type (#239) (#301) 
* Stable comparison of metadata (#239)

Iterating over a map in Go never produces twice the same ordering.
Thus when comparing two metadata map with more than one key, the
`differ` is always finding differences.

To properly compare records metadata, we need to iterate the maps
in a deterministic way.

Signed-off-by: Brice Figureau <brice@daysofwonder.com>

* Support for Route53 ALIAS record type (#239)

Route53 ALIAS doesn't behave like a regular ALIAS, and is much more
limited as its target can only be some specific AWS resources or
another record in the same zone.

According to #239, this change adds a new directive R53_ALIAS which
implements this specific alias. This record type can only be used
with the Route53 provider.

This directive usage looks like this:
```js
D("example.com", REGISTRAR, DnsProvider("ROUTE53"),
R53_ALIAS("foo1", "A", "bar") // record in same zone
R53_ALIAS("foo2", "A",
  "blahblah.elasticloadbalancing.us-west-1.amazonaws.com",
   R53_ZONE('Z368ELLRRE2KJ0')) // ELB in us-west-1

```

Unfortunately, Route53 requires indicating the hosted zone id
where the target is defined (those are listed in AWS documentation,
see the R53_ALIAS documentation for links).
2018-01-16 05:53:12 -05:00

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layout title
default ALIAS Records

ALIAS Records

ALIAS records are not widely standardized across DNS providers. Some (Route 53, DNSimple) have a native ALIAS record type. Others (Cloudflare) implement transparent CNAME flattening.

DNSControl adds an ALIAS record type, and leaves it up to the provider implementation to handle it.

A few notes:

  1. A provider must "opt-in" to supporting ALIAS records. When registering a provider, you specify which capabilities you support. Here is an example of how the cloudflare provider declares its support for aliases:
func init() {
	providers.RegisterDomainServiceProviderType("CLOUDFLAREAPI", newCloudflare, providers.CanUseAlias)
}
  1. If you try to use ALIAS records, all dns providers for the domain must support ALIAS records. We do not want to serve inconsistent records across providers.
  2. CNAMEs at @ are disallowed, but ALIAS is allowed.
  3. Cloudflare does not have a native ALIAS type, but CNAMEs behave similarly. The Cloudflare provider "rewrites" ALIAS records to CNAME as it sees them. Other providers may not need this step.
  4. Route 53 requires the use of R53_ALIAS instead of ALIAS.