Use an existing lambda function as datasource in Terraform - amazon-web-services

Question

I'm trying to use an existing Lambda function as a data source and create an EC2 instance. This Lambda function essentially provides the latest AMI.
I'm looking at this doc:
https://registry.terraform.io/providers/hashicorp/aws/latest/docs/data-sources/lambda_invocation
Source Block:
data "aws_lambda_invocation" "example" {
function_name = aws_lambda_function.resource_selector.ResourceSelector
input = <<JSON
{
"key1": "AMIRegexPattern"
}
JSON
}
output "result_entry" {
value = jsondecode(data.aws_lambda_invocation.example.result)["key1"]
}
It throws this error and I'm a little lost:
Error: Reference to undeclared resource
on create-ec2.tf line 26, in data "aws_lambda_invocation" "example":
26: function_name = aws_lambda_function.resource_selector.ResourceSelector
A managed resource "aws_lambda_function" "resource_selector" has not been
declared in the root module.
Here is the function details:
Function Name - ResourceSelector
Function ARN : arn:aws:lambda:us-east-1:xx50:function:ResourceSelector
Any help on what I am missing? Also curious on this line esp and if this is correct:
function_name = aws_lambda_function.resource_selector.ResourceSelector
Thanks

Answer 1

If the lambda is created outside terraform you have to hardcode or pass via parameter, like so:
function_name = "ResourceSelector"
aws_lambda_function.resource_selector doesn't exist, or you can manage the lambda defininng the aws_lambda_function resource.
Also if you just want to get the latest AMI you don't need a lambda. Terraform actually has a data source that can pull that for you: aws_ami
Example:
data "aws_ami" "example" {
most_recent = true
owners = ["self"]
filter {
name = "name"
values = ["myami-*"]
}
}