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When I create the VPC, I create a subnet in every availability zone.

Then, when I create my application, I want to input the ami and the type of instance (e.g. t3a.nano).

I want to avoid getting this error:

Error: Error launching source instance: Unsupported: Your requested instance type (a1.medium) is not supported in your requested Availability Zone (us-west-2b). Please retry your request by not specifying an Availability Zone or choosing us-west-2a, us-west-2c.

I am looking for a terraform module that can tell me if I can create my instance on this subnet given my ami and instance type.

I didn't find the terraform module one so I created my own. It is doing what I want but I wonder if there is a better way.

I put my code here. https://gitlab.com/korrident/terraform_calculate_ami_by_availability_zone

Quickly, I just use a data "external" to call a bash

data "external" "subnet_available_for_ami" {
  count = "${length(var.subnets_id)}"

  program = ["bash", "${path.module}/check_subnet_ami.bash"]

  query = {
    ami     = "${data.aws_ami.latest_ami.id}"
    type    = "${var.instance_type}"
    subnet  = "${var.subnets_id[count.index]}"
    region  = "${var.aws_region}"
    profile = "${var.aws_profile}"
  }
}

This script will call AWS CLI with a dry-run

aws --region=${REGION} ec2 run-instances \
--instance-type ${INSTANCE_TYPE} \
--image-id ${AMI} \
--subnet-id ${SUBNET_ID} \
--profile ${PROFILE} \
--dry-run

And in the end I filter the results to return a clean subnet list

locals {
  uniq_answers = "${distinct(data.external.subnet_available_for_ami.*.result)}"

  uniq_answers_filtered = [
    for a in local.uniq_answers :
    a if length(a) != 0
  ]

  uniq_subnet_filtered = [
    for a in local.uniq_answers_filtered :
    a.subnet
  ]
}

Note that in the same script I also use the component aws_ami.

data "aws_ami" "latest_ami" {

Ideally, I would like this component to return me an ami available on my subnets.

There is no error, it works fine but is minimal. If nothing is found, the calling module will deal with it. The most problematic case is when there is only one result (I want my instances to be on multiple availability zones, not just one).

Has anyone found a better design?

Vincent KERDRAON
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    Can you edit your question to include the full error you get when placing instances into AZs? – ydaetskcoR Jul 24 '19 at 18:11
  • @ydaetskcoR edited to add the exact error. this is returned by aws-sdk-go. – Vincent KERDRAON Jul 29 '19 at 17:23
  • The error shared here has nothing to do with the AMI - only the instance type. It's saying that the type of instance (a1.medium) is not available in that zone. IIRC a1.medium and t3a.nano types use AMD processors and have limited availability within each zone and region. It likely indicates exhausted AMD resources in a particular zone or region. In this case, trying another AZ, region or raising a support ticket to AWS may encourage them to increase capacity. – doughgle May 10 '20 at 07:15

0 Answers0