aws: Add support for Alias records into AWS Route 53

[radeksimko]

This closes #747
Documentation attached.

Alias records (as documented) can be currently used in conjunction with

• ELBs - one extra commit here is allowing it to happen by exposing zone_id
• existing R53 records (works out of the box)
• CloudFront distributions - see providers/aws: CloudFront distribution #1780 (comment)
• S3 buckets - see aws/s3_bucket: Expose region + hosted zone ID #1769

Test plan

$ make testacc TEST=./builtin/providers/aws TESTARGS='-run=Route53Record' 2>/dev/null

go generate ./...
TF_ACC=1 go test ./builtin/providers/aws -v -run=Route53Record -timeout 45m
=== RUN TestAccRoute53Record
--- PASS: TestAccRoute53Record (260.16s)
=== RUN TestAccRoute53Record_txtSupport
--- PASS: TestAccRoute53Record_txtSupport (279.02s)
=== RUN TestAccRoute53Record_generatesSuffix
--- PASS: TestAccRoute53Record_generatesSuffix (269.83s)
=== RUN TestAccRoute53Record_wildcard
--- PASS: TestAccRoute53Record_wildcard (402.11s)
=== RUN TestAccRoute53Record_weighted
--- PASS: TestAccRoute53Record_weighted (266.97s)
=== RUN TestAccRoute53Record_alias
--- PASS: TestAccRoute53Record_alias (529.72s)
=== RUN TestAccRoute53Record_weighted_alias
--- PASS: TestAccRoute53Record_weighted_alias (521.43s)
PASS
ok      github.com/hashicorp/terraform/builtin/providers/aws    2529.257s

Example

resource "aws_route53_zone" "main" {
  name = "notexample.com"
}

resource "aws_route53_record" "alias" {
  zone_id = "${aws_route53_zone.main.zone_id}"
  name = "www"
  type = "A"

  alias {
    zone_id = "${aws_elb.main.zone_id}"
    name = "${aws_elb.main.dns_name}"
    evaluate_target_health = true
  }
}

resource "aws_elb" "main" {
  name = "foobar-terraform-elb"
  availability_zones = ["us-west-2a"]

  listener {
    instance_port = 80
    instance_protocol = "http"
    lb_port = 80
    lb_protocol = "http"
  }
}

Related PR: #1366. I hope I covered all the edge cases and conflicts (e.g. TTL).

[mitchellh]

Looks perfect!

[radeksimko]

@c4milo I see your point, sorry for the troubles caused. I was actually thinking about this problem, but it's not just related to this resource, it's a global issue affecting many other resources as well.

There is simply nothing like RequiredWhen yet where we could say "this is only required if property X == Y" or "one of these fields is required". I agree that the Schema desperately needs such functionality. I may have a look into it this weekend.

also, this change is currently misaligned with what the documentation says.

could you be a bit more specific, please?

[c4milo]

@radeksimko I didn't mean it in a negative way, I should've used a different word instead of "waste". It just took me longer than normal to realize what was going on. So, there is nothing to be sorry about :)

Regarding the documentation, I think it only needs to make more explicit that ttl and records attributes are required only if there is not an ALIAS block present.

[radeksimko]

@c4milo Regarding docs -> see #2092

I was already adding ConflictsWith for similar purpose, so I'd expect it should tell you that these parameters conflict with each other. If it doesn't, then there must be a bug in that implementation.

[c4milo]

@radeksimko, yes, I tested that case and it complains about conflicting configuration options correctly.

[ghost]

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