Add the ability to define a default value for undefined parameters

[hschimpf]

Hello!

I'm thinking about the possibility to define a default value for parameters that don't exist on SSM.

• [x] I'll be making the required changes on this PR.

Just have one question:

• What character we could define as separator for the parameter name and the default value?

• Since the name can't have the colon symbol in it, you think that it could be the separator @mnapoli?

  

[mnapoli]

Thanks for the PR! I'm afraid this is extra logic to maintain, and the feature doesn't have great DX (creating a special syntax) 🤔

What is the use case for you? Where have you seen that need?

[hschimpf]

What is the use case for you? Where have you seen that need?

As serverless allows to set default values on variables, I already have some variables that have a default value when it's not present on the .env file.

For example, these are my current serverless.yml environment variables:

serverless.yml

provider:
  environment:
    DB_HOST: ${env:SLS_DB_HOST}
    DB_DATABASE: ${env:SLS_DB_DATABASE, self:custom.UUID}
    DB_USERNAME: ${env:SLS_DB_USERNAME, self:custom.UUID}
    DB_PASSWORD: ${env:SLS_DB_PASSWORD}

custom:
  UUID: ${self:service}-${self:provider.stage}

The UUID is generated using the service name and the current deployment stage. So when I deploy to production, the username and database is generated from the UUID. And if in the CI/CD the SLS_DB_DATABASE or SLS_DB_USERNAME is set, it will be used instead of the default value.

I want to update those values to bref-ssm to store them on AWS SSM Parameters, and if they don't exist, use the generated value using UUID like this:

serverless.yml

provider:
  environment:
    DB_HOST: bref-ssm:/${param:UUID}/DB_HOST
    DB_PORT: bref-ssm:/${param:UUID}/DB_PORT,3306
    DB_DATABASE: bref-ssm:/${param:UUID}/DB_DATABASE,${self:custom.UUID}
    DB_USERNAME: bref-ssm:/${param:UUID}/DB_USERNAME,${self:custom.UUID}
    DB_PASSWORD: bref-ssm:/${param:UUID}/DB_PASSWORD

custom:
  UUID: ${self:service}-${self:provider.stage}