AWS SAM Template setting environment specific variables

Question

I am trying to configure a Lambda function's S3 policy bucket that is environment specific. I would like to be able to pass a variable during either "sam package" or "sam deploy" specifying "dev", "test" or "prod". The variable would be used in the template.yaml file to select environment specific settings:

AWSTemplateFormatVersion: '2010-09-09'
Transform: AWS::Serverless-2016-10-31
Description: >
  image-processing


Resources:
  ImageProcessingFunction:
    Type: AWS::Serverless::Function
    Properties:
      Handler: src/handlers/image-processing.handler
      Runtime: nodejs12.x
      CodeUri: .
      MemorySize: 256
      Timeout: 300
      Policies:
        S3CrudPolicy:
          BucketName: dev-bucket-name  <-- change this to dev, test or prod

How can I achieve this using Parameters and or Variables? Thank you.

Answer 1

You should use —parameter-overrides in your sam deploy command.

sam deploy cli

Let me demonstrate how:

In your template.yaml:

Parameters:
Env:
    Type: String

S3Bucket:
    Type: String

Resources:

ImageProcessingFunction:
    Type: AWS::Serverless::Function
    Properties:
      Handler: src/handlers/image-processing.handler
      Runtime: nodejs12.x
      CodeUri: .
      MemorySize: 256
      Timeout: 300
      Policies:
        S3CrudPolicy:
          BucketName: !Sub "${Env}-${S3Bucket}"

Then execute:

sam deploy --template-file packaged.yaml --stack-name yourstack --capabilities CAPABILITY_IAM --parameter-overrides Env=dev S3Bucket=bucket-name

If you want to pass your parameters from a .json file per env you should consider using cross-env ENV=dev to pass your Env variable and then using gulp or whatever to execute your sam deploy --parameter-overrides command while passing your json file according to your Env variable (process.env.ENV) (converted to how parameters overrides pattern ) as parameter-overrides params.

Hope this helps