How to use an existing ECR image in my AWS account when using AWS SAM to define Lambda Function resource backed by container image

Question

I'm following the tutorial linked below and would like to know if it is possible to reference a prebuilt ECR image for a Lambda function resource rather than the image being built by AWS SAM on deployment.

For example, is it possible to reference an existing ECR image in my AWS account built by another CI/CD pipeline?

What parts of the YAML template would I need to modify to achieve this if possible?

https://aws.amazon.com/blogs/compute/using-container-image-support-for-aws-lambda-with-aws-sam/

AWSTemplateFormatVersion: '2010-09-09'
Transform: AWS::Serverless-2016-10-31
Description: demo app
  
Globals:
  Function:
    Timeout: 3

Resources:
  HelloWorldFunction:
    Type: AWS::Serverless::Function
    Properties:
      PackageType: Image
      Events:
        HelloWorld:
          Type: Api
          Properties:
            Path: /hello
            Method: get
    Metadata:
      DockerTag: nodejs12.x-v1
      DockerContext: ./hello-world
      Dockerfile: Dockerfile
      
  HolaWorldFunction:
    Type: AWS::Serverless::Function
    Properties:
      PackageType: Image
      Events:
        HolaWorld:
          Type: Api
          Properties:
            Path: /hola
            Method: get
    Metadata:
      DockerTag: nodejs12.x-v1
      DockerContext: ./hola-world
      Dockerfile: Dockerfile

Outputs:
  HelloWorldApi:
    Description: "API Gateway endpoint URL for Prod stage for Hello World function"
    Value: !Sub "https://${ServerlessRestApi}.execute-api.${AWS::Region}.amazonaws.com/Prod/hello/"
  HolaWorldApi:
    Description: "API Gateway endpoint URL for Prod stage for Hola World function"
    Value: !Sub "https://${ServerlessRestApi}.execute-api.${AWS::Region}.amazonaws.com/Prod/hola/"

Answer 1

There is an ImageUri field in the function Properties that lets you specify the ECR image. Additionally you can overwrite some image parameters like Command. Note that I used environment variables in the buildstep and pulled those in as parameters for the account ID and image tag in this example

Properties:
      ImageUri: !Sub ${AccountIDParameter}.dkr.ecr.us-west-2.amazonaws.com/lambda:${EnvironmentParameter}
      ImageConfig:
        Command: [ "app.CommandOverwrite" ]