Add Aurora Postgresql Serverless Example

[daveyu]

This config worked for me:

module "aurora_postgres_serverless" {
  source                   = "git::https://github.com/cloudposse/terraform-aws-rds-cluster.git?ref=tags/0.15.0"
  namespace                = "${var.namespace}"
  stage                    = "${var.stage}"
  name                     = "${var.postgres_name}"
  engine                   = "aurora-postgresql"
  engine_mode              = "serverless"
  engine_version           = "10.7"
  cluster_family           = "aurora-postgresql10"
  cluster_size             = "0"
  admin_user               = "${local.postgres_admin_user}"
  admin_password           = "${local.postgres_admin_password}"
  db_name                  = "${local.postgres_db_name}"
  db_port                  = "5432"
  vpc_id                   = "${data.terraform_remote_state.backing_services.vpc_id}"
  subnets                  = ["${data.terraform_remote_state.backing_services.public_subnet_ids}"]
  zone_id                  = "${local.zone_id}"
  publicly_accessible      = "true"
  allowed_cidr_blocks      = ["0.0.0.0/0"]
  enabled                  = "${var.postgres_cluster_enabled}"

  scaling_configuration = [
    {
      auto_pause               = true
      max_capacity             = "384"
      min_capacity             = "8"
      seconds_until_auto_pause = 300
    }
  ]
}

Valid capacity units for Postgres are 8, 16, 32, 64, 192, and 384, per https://docs.aws.amazon.com/AmazonRDS/latest/AuroraUserGuide/aurora-serverless.create.html

[osterman]

Thanks @daveyu ! This is great.

[daveyu]

Oh, there was an error with applying the module though:

* module.aurora_postgres.module.dns_replicas.aws_route53_record.default: 1 error(s) occurred:

* aws_route53_record.default: [ERR]: Error building changeset: InvalidChangeBatch: [Invalid Resource Record: FATAL problem: DomainNameEmpty (Domain name is empty) encountered with '', Unparseable CNAME encountered]
	status code: 400, request id: 67f88f1e-d3b5-4c8b-bc79-4c72a48a7e27

EDIT: I see this is fixed in 0.16.0.

[bionicles]

@osterman @aknysh @goruha hey all -- can we add this Serverless PostgreSQL to the readme and include the enable_http_endpoint parameter so we can use the Data API? I was gonna use this for a startup and make a little script to do schema / ddl migrations with Data API. Postgres is in style these days

Then you could close #54 and #51