How to specify AutoPublishAlias at runtime of 'sam package/deploy'? - aws-lambda

Question

I am wrapping our AWS SAM deployment in Jenkins as part of our CI/CD pipeline. I only want to add the "live" alias to the lambdas when we are merging for example, yet I want "branch builds" to be without an alias. This allows developers to test the code in AWS without it being "live". Other than sed replacing part of the template.yaml before I run "sam package/deploy" is there some other way to accomplish this?
--UPDATE--
It looks like I can use Parameters to create environments in my lambda, but I don't know how to toggle between them. This would look like:
Parameters:
MyEnv:
Description: Environment of this stack of resources
Type: String
Default: testing
AllowedValues:
- testing
- prod
Then I can reference this w/:
Environment:
Variables:
ENV: !Ref: MyEnv
If someone knows how to toggle this parameter at runtime that solves my problem.

Answer 1

I got this working. My template.yaml:
AWSTemplateFormatVersion: '2010-09-09'
Transform: AWS::Serverless-2016-10-31
Description: >
sams-app
Globals:
Function:
Timeout: 3
Parameters:
Stage:
Type: String
Description: Which stage the code is in
Default: test
AllowedValues:
- test
- prod
Resources:
HelloWorldSQSFunction:
Type: AWS::Serverless::Function
Properties:
Role: arn:aws:iam::xxxxxxxxxxxx:role/service_lambda_default1
CodeUri: hello_world/
Handler: app.lambda_handler
Runtime: python3.7
AutoPublishAlias: !Ref Stage
DeploymentPreference:
Type: AllAtOnce
Environment:
Variables:
STAGE: !Ref Stage
Outputs:
HelloWorldSQSFunction:
Description: "Hello World SQS Lambda Function ARN"
Value: !GetAtt HelloWorldSQSFunction.Arn
My lambda code:
import json
import os
def lambda_handler(event, context):
stage = os.environ['STAGE']
print(f"My stage is: {stage}")
return {
"statusCode": 200,
}
And to run it locally (I'm using Cloud9):
DEVELOPER:~/environment/sams-app $ sam local invoke --parameter-overrides Stage=prod
Invoking app.lambda_handler (python3.7)
Fetching lambci/lambda:python3.7 Docker container image......
Mounting /home/ec2-user/environment/sams-app/hello_world as /var/task:ro,delegated inside runtime container
START RequestId: 85da81b1-ef74-1b7d-6ad0-a356f4aa8b76 Version: $LATEST
My stage is: prod
END RequestId: 85da81b1-ef74-1b7d-6ad0-a356f4aa8b76
REPORT RequestId: 85da81b1-ef74-1b7d-6ad0-a356f4aa8b76 Init Duration: 127.56 ms Duration: 3.69 ms Billed Duration: 100 ms Memory Size: 128 MB Max Memory Used: 22 MB
{"statusCode":200}
One thing to note is that this will cause your "sam validate" to fail. For info on that, see: https://github.com/awslabs/serverless-application-model/issues/778
Special thanks to JLarky for the comment on this thread: aws-sam-local environment variables