RDS replica creation requires double apply

[bethge]

Terraform Version

Terraform v0.11.1
+ provider.aws v1.6.0

Affected Resource(s)

• aws_db_instance

Terraform Configuration Files

provider "aws" {
  region = "us-east-1"
}

resource "aws_vpc" "main" {
  cidr_block = "10.0.0.0/16"
}

resource "aws_subnet" "main-a" {
  vpc_id            = "${aws_vpc.main.id}"
  availability_zone = "us-east-1a"
  cidr_block        = "10.0.1.0/24"
}

resource "aws_subnet" "main-b" {
  vpc_id            = "${aws_vpc.main.id}"
  availability_zone = "us-east-1b"
  cidr_block        = "10.0.2.0/24"
}

resource "aws_db_subnet_group" "main" {
  subnet_ids = ["${aws_subnet.main-a.id}", "${aws_subnet.main-b.id}"]
}

resource "aws_db_instance" "master" {
  allocated_storage       = 10
  engine                  = "mysql"
  instance_class          = "db.t2.micro"
  username                = "foo"
  password                = "barbar12"
  backup_retention_period = 1
  apply_immediately       = true
  db_subnet_group_name    = "${aws_db_subnet_group.main.name}"
}

resource "aws_db_instance" "replica" {
  replicate_source_db = "${aws_db_instance.master.identifier}"
  allocated_storage   = 15
  instance_class      = "db.t2.micro"
}

Expected Behavior

There are no changes to be applied after an execution of terraform apply.

Actual Behavior

There are changes to be applied:

  ~ aws_db_instance.replica
      allocated_storage: "10" => "15"

Steps to Reproduce

1. terraform apply
2. terraform plan

Important Factoids

• The CreateDBInstanceReadReplica action only allows for a subset of parameters to be applied on creation.

Iiuc the limitations of the CreateDBInstanceReadReplica AWS API call is the issue. Certain parameters can not be configured during DB creation but must be changed after creation. Is there some way for terraform to circumvent the limitations of the AWS API in this situation? E.g. by creating and then updating the db_instance in one apply execution.

I would be more than willing to work on a PR to resolve this issue, assuming it is within the realm of fixability.

[Bryji]

I'm having a similar issue (as linked above in the terraform-aws-rds repo), read replicas in a multi-region MySQL set up have multi-az set to false. It looks like it remains false after re-applying config also (but on one occasion the change did take after a re-apply).

[bflad]

The fix for this has been merged into master and will release with version 1.34.0 of the AWS provider, likely later today.

[bflad]

This has been released in version 1.34.0 of the AWS provider. Please see the Terraform documentation on provider versioning or reach out if you need any assistance upgrading.

[ghost]

I'm going to lock this issue because it has been closed for 30 days ⏳. This helps our maintainers find and focus on the active issues.

If you feel this issue should be reopened, we encourage creating a new issue linking back to this one for added context. Thanks!