Adding a new aws opsworks instances forces all the other instances to be re-created

[iroller]

Hi there,

I'm trying to have aws_opsworks_instance, aws_subnet and aws_route_table_association to be created depending on a number set in variables, but once I add one more I'm always getting all the instances re-created all over again:

    subnet_id:                    "subnet-ed8bacd0" => "${element(aws_subnet.private.*.id, count.index)}" (forces new resource)

Here's my config:

# Create private associations
resource "aws_route_table_association" "private" {
  count = "${var.instance_count}"
  subnet_id = "${element(aws_subnet.private.*.id, count.index)}"
  route_table_id = "${aws_route_table.nat-private.id}"
  lifecycle {
    create_before_destroy = true
  }
}

# Create private subnets for app instances
resource "aws_subnet" "private" {
  count = "${var.instance_count}"
  vpc_id = "${aws_vpc.my-vpc.id}"
  availability_zone = "${lookup(var.instances, count.index)}"
  cidr_block = "${concat(var.vpc_cidr_block_base, ".", count.index + 1 ,".0/24")}"
  map_public_ip_on_launch = false
  tags {
    Name = "private.${lookup(var.instances, count.index)}"
    Environment = "${var.environment}"
  }
  lifecycle {
    create_before_destroy = true
  }
}


# Instances
resource "aws_opsworks_instance" "app" {
  stack_id = "${aws_opsworks_stack.my-stack.id}"
  layer_ids = [
    "${aws_opsworks_rails_app_layer.app.id}",
  ]
  availability_zone = "${lookup(var.instances, count.index)}"
  subnet_id = "${element(aws_subnet.private.*.id, count.index)}"
  instance_type    = "t2.small"
  os               = "Ubuntu 14.04 LTS"
  state            = "running"
  root_device_type = "ebs"
  count = "${var.instance_count}"
}

And variables:

variable "instances" {
  description = "OpsWorks App instances"
  default     = {
    "0" = "us-east-1e"
    "1" = "us-east-1a"
    "2" = "us-east-1c"
    "3" = "us-east-1c" # re-creates all the instances once I'm adding that
  }
}
# Still need to provide that until we can figure out how to count instanced in the map above
variable "instance_count" {
  description = "Count"
  default     = "4"
}

When I'm running terraform plan with v. 0.6.16 it's showing that each opsworks instance is going to be re-created and the new one will be added.

How to prevent it from re-creating all the existing instances?

[iroller]

Latest master is failing with the following:

  * concat: arguments to concat() must be a string or list in:
${concat(var.vpc_cidr_block_base, ".", count.index + 1, ".0/24")}

EDIT: can be worked around by using format() instead of concat() but the initial issue with re-creating instances is still there.

[iroller]

Also this is not happening on every terraform plan, only when adding a new instance into var.instances and bumping var.instance_count.

[iroller]

I figured this problem was mentioned in many issues before. The workaround suggested by @apparentlymart works fine. In this case it looks like this:

terraform apply -target="aws_opsworks_instance.app[3]" -target="aws_subnet.private[3]" -target="aws_route_table_association.private[3]"

[catsby]

Hey @iroller thanks for the detailed report here. It looks like the core issue is here:

• Using element with splat reference should scope dependency to selected resource #3449

This may be fixed in the master branch and released with v0.7.0, though I believe you need to use the newly introduced (in v0.7.0) list type (added here #6322)

For now though the workaround is your best bet. Since this is tracked elsewhere, I'm going to go ahead and close this. Thanks again!

[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 have found a problem that seems similar to this, please open a new issue and complete the issue template so we can capture all the details necessary to investigate further.