my_template.yaml

AWSTemplateFormatVersion: 2010-09-09
Description: CloudFormation template for a S3 bucket 
    
Resources:
  MyS3Bucket:
    Type: AWS::S3::Bucket
    Properties:
      BucketName: i-named-this-bucket-1337


  MyLambda:
    Type: AWS::Lambda::Function
    Properties:
      FunctionName: "my-function"
      Handler: index.handler
      Code:
        ZipFile: |
          var AWS = require("aws-sdk");
          var s3 = new AWS.S3();
          exports.handler = function(event, context) {
            s3.listObjects({ Bucket: process.env.S3_BUCKET},
              function (err, data) {
                if (err) throw err;
                console.log(data)
              })
            console.log("I'm a lambda!")
          };
      Runtime: nodejs14.x
      Role: !GetAtt LambdaExecutionRole.Arn
      Environment:
        Variables:
          S3_BUCKET: !Ref MyS3Bucket

  LambdaExecutionRole:
    Type: AWS::IAM::Role
    Properties:
      AssumeRolePolicyDocument:
        Version: '2012-10-17'
        Statement:
        - Effect: Allow
          Principal:
            Service:
            - lambda.amazonaws.com
          Action:
          - sts:AssumeRole
      Path: "/"
      Policies:
      - PolicyName: root
        PolicyDocument:
          Version: '2012-10-17'
          Statement:
          - Effect: Allow
            Action:
            - logs:*
            Resource: arn:aws:logs:*:*:*
      - PolicyName: list-s3
        PolicyDocument:
          Version: '2012-10-17'
          Statement:
            - Effect: Allow
              Action:
                - s3:List*
              Resource: !GetAtt MyS3Bucket.Arn