AWS Lambda: Support Fn::Split in `vpc.securityGroupIds` and `vpc.subnetIds` configurations

[vmj]

sls produces correct CloudFormation, but issues a configuration warning. This has been discussed and fixed in issue #8282 but I guess Split function slipped the radar.

serverless.yml

service: hello-world
frameworkVersion: '2'

provider:
  name: aws
  runtime: nodejs12.x
  vpc:
    subnetIds: !Split
      - ','
      - "sn1,sn2"
    securityGroupIds: !Split
      - ','
      - "sg1,sg2"

functions:
  hello:
    handler: handler.hello

output

✔ ~/src/testing/serverless-fw/hello-world ➭ sls package
Serverless: Configuration warning:
Serverless:   at 'provider.vpc.securityGroupIds': should be array
Serverless:   at 'provider.vpc.subnetIds': should be array
Serverless:
Serverless: Learn more about configuration validation here: http://slss.io/configuration-validation
Serverless:
Serverless: Packaging service...
Serverless: Excluding development dependencies...

Installed version

Framework Core: 2.11.1 (local)
Plugin: 4.1.2
SDK: 2.3.2
Components: 3.3.0

[medikoo]

@vmj thanks for reporting. Indeed as we pass those setting as is to CloudFormation template, we should openly support functions as Fn::Split.

Question is what else in terms of intrinsic functions should be supported in such case?

[vmj]

@medikoo Ah, I missed that it is the short form !Split that triggers the warning, and Fn::Split works without a warning. Thanks!

I'll take a look over the weekend if I manage to produce a PR, unless someone beats me to it. I'm not at all familiar with the code base but I'm thinking of making short form work the same as long form. Or do you already know it won't work?

[medikoo]

@vmj In my understanding !Split is resolved to Fn::Split before config validation, and it's Fn::Split notation that is not recognized.

In config schema we support only array notation currently:

serverless/lib/plugins/aws/provider/awsProvider.js

Line 431 in 3feafbc

type: 'array',

[vmj]

@medikoo I just tried a couple of times, and !Split triggers a warning, Fn::Split does not.