Add option to allow no results when querying aws_instances Data Source

[coop182]

Changes proposed in this pull request:

• Add allow_no_results option to aws_instances Data Source

Output from acceptance testing:

$ make testacc TESTARGS='-run=TestAccAWSInstancesDataSource_noResults'
==> Checking that code complies with gofmt requirements...
TF_ACC=1 go test ./... -v -run=TestAccAWSInstancesDataSource_noResults -timeout 120m
?   	github.com/terraform-providers/terraform-provider-aws	[no test files]
=== RUN   TestAccAWSInstancesDataSource_noResults
--- PASS: TestAccAWSInstancesDataSource_noResults (32.55s)
PASS
ok  	github.com/terraform-providers/terraform-provider-aws/aws	32.596s

[catsby]

Hey there @coop182 ! Could you elaborate some on the possible use cases for this? The docs included mention "querying the count of ephemeral instances", how would you imagine this count is later used? Thanks 😄

[coop182]

Hey @catsby,

This would be really useful when doing rolling ASG deploys as outlined here - which implements the strategy outline by @phinze here.

Effectively being able to query the aws_instances data source without it throwing an error when no instances are found would allow it to be used to dynamically size the new ASG to the same size as the current ASG.

For example if I have a min_size of 1 and max_size of 20 and a desired_capacity that moves between those numbers constantly via auto scaling policies at the moment I can see no way to set the new ASG to the exact desired capacity required at the point in time of the deploy... this leads to either having to over or under provision the number of instances on a rolling ASG deploy.

Maybe I have missed a better way to do or think about this?

Example code:

# Get most recent Ubuntu AMI
data "aws_ami" "ubuntu" {
  most_recent = true

  filter {
    name   = "name"
    values = ["ubuntu/images/hvm-ssd/ubuntu-xenial-16.04-amd64-server-*"]
  }

  filter {
    name   = "virtualization-type"
    values = ["hvm"]
  }

  filter {
    name   = "state"
    values = ["available"]
  }

  owners = ["099720109477"] # Canonical
}

# Create Launch Configuration from latest AMI
resource "aws_launch_configuration" "lc" {
  image_id                    = "${data.aws_ami.ami.id}"
  instance_type               = "t2.small"
  key_name                    = "${var.key_name}"
  security_groups             = ["${var.security_groups}"]

  lifecycle {
    create_before_destroy = true
  }
}

# Get the instances currently in the Autoscaling group based on the Launch configuration name
data "aws_instances" "asg" {
  filter {
    name   = "instance-state-name"
    values = ["running"]
  }

  filter {
    name   = "tag-value"
    values = ["${aws_launch_configuration.lc.id}"]
  }

  allow_no_results = true
}

# Create an autoscaling group - initially with a desired capacity of one but on further updates the desired capacity will be maintained when ASG is replaced.
resource "aws_autoscaling_group" "asg" {
  health_check_grace_period = 500
  health_check_type         = "ELB"
  launch_configuration      = "${aws_launch_configuration.lc.id}"
  max_size                  = 20
  min_size                  = 1
  desired_capacity          = "${length(data.aws_instances.asg.ids) == 0 ? 1 : length(data.aws_instances.asg.ids)}"
  min_elb_capacity          = "${length(data.aws_instances.asg.ids) == 0 ? 1 : length(data.aws_instances.asg.ids)}"
  name                      = "${aws_launch_configuration.lc.id}"
  vpc_zone_identifier       = ["${var.network_subnets}"]
  target_group_arns         = ["${aws_lb_target_group.main.arn}"]

  lifecycle {
    create_before_destroy = true
  }
}

[coop182]

Any more feedback @catsby or @bflad?

[zhelding]

Pull request #21306 has significantly refactored the AWS Provider codebase. As a result, most PRs opened prior to the refactor now have merge conflicts that must be resolved before proceeding.

Specifically, PR #21306 relocated the code for all AWS resources and data sources from a single aws directory to a large number of separate directories in internal/service, each corresponding to a particular AWS service. This separation of code has also allowed for us to simplify the names of underlying functions -- while still avoiding namespace collisions.

We recognize that many pull requests have been open for some time without yet being addressed by our maintainers. Therefore, we want to make it clear that resolving these conflicts in no way affects the prioritization of a particular pull request. Once a pull request has been prioritized for review, the necessary changes will be made by a maintainer -- either directly or in collaboration with the pull request author.

For a more complete description of this refactor, including examples of how old filepaths and function names correspond to their new counterparts: please refer to issue #20000.

For a quick guide on how to amend your pull request to resolve the merge conflicts resulting from this refactor and bring it in line with our new code patterns: please refer to our Service Package Refactor Pull Request Guide.

[ewbankkit]

@coop182 Thanks for the contribution 🎉 👏.
I have rolled your changes into #21219.

[github-actions]

This functionality has been released in v4.0.0 of the Terraform AWS Provider. Please see the Terraform documentation on provider versioning or reach out if you need any assistance upgrading.

For further feature requests or bug reports with this functionality, please create a new GitHub issue following the template. Thank you!

[github-actions]

I'm going to lock this pull request 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 related to this change, please open a new issue and complete the issue template so we can capture all the details necessary to investigate further.