The subnet does not exist error in terraform - amazon-web-services

Question

I want to create elastic beanstalk with tf. Here is the main.tf
resource "aws_elastic_beanstalk_application" "elasticapp" {
name = var.elasticapp
}
resource "aws_elastic_beanstalk_environment" "beanstalkappenv" {
name = var.beanstalkappenv
application = aws_elastic_beanstalk_application.elasticapp.name
solution_stack_name = var.solution_stack_name
tier = var.tier
setting {
namespace = "aws:ec2:vpc"
name = "VPCId"
value = var.vpc_id
}
setting {
namespace = "aws:ec2:vpc"
name = "Subnets"
value = var.public_subnets
}
setting {
namespace = "aws:elasticbeanstalk:environment:process:default"
name = "MatcherHTTPCode"
value = "200"
}
setting {
namespace = "aws:elasticbeanstalk:environment"
name = "LoadBalancerType"
value = "application"
}
setting {
namespace = "aws:autoscaling:launchconfiguration"
name = "InstanceType"
value = "t2.micro"
}
setting {
namespace = "aws:ec2:vpc"
name = "ELBScheme"
value = "internet facing"
}
setting {
namespace = "aws:autoscaling:asg"
name = "MinSize"
value = 1
}
setting {
namespace = "aws:autoscaling:asg"
name = "MaxSize"
value = 2
}
setting {
namespace = "aws:elasticbeanstalk:healthreporting:system"
name = "SystemType"
value = "enhanced"
}
}
I have variables defined in vars.tf.
This is the provider.tf
provider "aws" {
region = "eu-west-3"
}
When I try to apply I get the following message
Error: ConfigurationValidationException: Configuration validation exception: Invalid option value: 'subnet-xxxxxxxxxxxxxxx' (Namespace: 'aws:ec2:vpc', OptionName: 'ELBSubnets'): The subnet 'subnet-xxxxxxxxxxxxxxx' does not exist.
│ status code: 400, request id: be485042-a653-496b-8510-b310d5796eef
│
│ with aws_elastic_beanstalk_environment.beanstalkappenv,
│ on main.tf line 9, in resource "aws_elastic_beanstalk_environment" "beanstalkappenv":
│ 9: resource "aws_elastic_beanstalk_environment" "beanstalkappenv" {
I created the subnet inside the vpc that I provided in main.tf.
EDIT: I have only one subnet.
EDIT: adding vars.tf
variable "elasticapp" {
default = "pos-eb"
}
variable "beanstalkappenv" {
type = string
default = "pos-eb-env"
}
variable "solution_stack_name" {
type = string
default = "64bit Amazon Linux 2 v3.2.0 running Python 3.8"
}
variable "tier" {
type = string
default = "WebServer"
}
variable "vpc_id" {
default = "vpc-xxxxxxxxxxx"
}
variable "public_subnets" {
type = string
default = "subnet-xxxxxxxxxxxxxxx"
}

Answer 1

Ok, so first, check if the error message is correct.
As mentioned above, there is a chance you are working in the wrong account/region.
So check if terraform can find that subnet by using a datasource:
data "aws_subnet" "selected" {
id = var.public_subnets # based on your code above, this is a single subnet_id
}
output "subnet_detail" {
value = data.aws_subnet.selected
}
If the above code fails, that means terraform is not able to use/find that subnet.
So, if the subnet was created by terraform there is a chance regions/alias/account got mixed on the way to this module.
If it was manually created and you are only using the ID as manually inputted string, than the chances are that you copied the wrong subnet_id, vpc_id or that you are working in the wrong account/region.
If the above return data, and terraform can indeed find that subnet, check if it belongs to the VPC you are using on elastic_beanstalk.
If all the above is correct, than the issue may by in the "aws_elastic_beanstalk_environment" definition.
As you have an ELBScheme but you don't have the rest of the fields related to that ELB it could be throwing an error.
Since ELBSubnets was not provided in the "aws_elastic_beanstalk_environment" definition, it may be trying to use a default subnet from the default vpc.