Split-Up / Include / Reference serverless.yml file?

Hi. I had the same issue and this works for me.

serverless.yml

service:
  name: pow

provider:
  name: aws
  runtime: nodejs8.10

resources:
    ${file(./main-config.yml)}

main-config.yml

 - ${file(./part1.yml)}
 - ${file(./part2.yml)}
....

part1.yml

Resources:
  Test1:
    Type: AWS::S3::Bucket
    Properties:
      BucketName: lkawjef-aa11

part2.yml

Resources:
  Test2:
    Type: AWS::S3::Bucket
    Properties:
      BucketName: lkawjef-aaz7zzz