auto determine Lambda Layer ARN

Question

We can add AWS provided layers to lambda via console.
below is the line for cloudformation

```
Layers:
        - arn:aws:lambda:us-east-2:590474943231:layer:AWS-Parameters-and-Secrets-Lambda-Extension:4
```

where we can directly put ARN.

but how to determine automatically based on name and version? so we we can have it dynamically for different region as well.

tried same to determine using terraform as well but no luck

```
 data "aws_lambda_layer_version" "existing_security_layer" {
   layer_name = "AWS-Parameters-and-Secrets-Lambda-Extension"
  version= 4
}
```

Answer

The ARN for a Lambda layers is constructed as follows. Using this information you can construct the right ARN to put into things like CloudFormation and CDK.

`arn:PARTITION:REGION:ACCOUNT:layer:LAMBDA-LAYER-NAME:VERSION`

- If you're operating in the AWS commercial regions (which is everything except our China regions and GovCloud) then `REGION` will be "aws".
 - `REGION` is the region name that the Lambda Layer is deployed in.
 - `ACCOUNT` is the account number that you're operating in.
 - `LAMBDA_LAYER_NAME` is the name of the layer.
 - `VERSION` is the version that you want to reference.

You can find more information about how ARNs are constructed here: https://docs.aws.amazon.com/IAM/latest/UserGuide/reference-arns.html

You can also call the Lambda service using the `ListLayers` API to look for the current version of the Lambda Layer.

auto determine Lambda Layer ARN

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