Serverless environment variable scope

Question

We have one yaml file that has 1 service with several lambda function definitions. I'm trying to define an environment variable under one function, and was hoping that could be picked up in the iamrole statement, but I got Value not found at "env" source. But I need the variable to be defined at each function level. Is there a way we could achieve that. Our yml looks like

service: myService

frameworkVersion: "3"

provider:
  name: aws
  ...
  iamRoleStatements:
    - Fn::If:
        - myCondition
        - Effect: "Deny"
          Action:
            - ...
          Resources:
            - ...
resources:
  Conditions:
    myCondition: !Equals ["${env:MY_ENV_VARIABLE, false}", true]


functions:
  my_function:
    ...
    environment:
      MY_ENV_VARIABLE: true  

Thanks a lot!

Answer 1

You can simply define that value in custom section of yaml file and then pick it up from there:

service: myService

frameworkVersion: "3"

custom:
  myEnvVariable: true

provider:
  name: aws
  ...
  iamRoleStatements:
    - Fn::If:
        - myCondition
        - Effect: "Deny"
          Action:
            - ...
          Resources:
            - ...

resources:
  Conditions:
    myCondition: !Equals ["${self:custom.myEnvVariable, false}", true]


functions:
  my_function:
    ...
    environment:
      MY_ENV_VARIABLE: ${self:custom.myEnvVariable}  

However I see that basing on this: ["${env:MY_ENV_VARIABLE, false}", true], your variable might be not set in some cases. If it depends on the stage, you can simply use params section:

service: myService

frameworkVersion: "3"

params:
  default:
    MY_ENV_VARIABLE: true
  staging:
    MY_ENV_VARIABLE: true
  prod:
    MY_ENV_VARIABLE: false

provider:
  name: aws
  ...
  iamRoleStatements:
    - Fn::If:
        - myCondition
        - Effect: "Deny"
          Action:
            - ...
          Resources:
            - ...

resources:
  Conditions:
    myCondition: !Equals ["${param:MY_ENV_VARIABLE}", true]


functions:
  my_function:
    ...
    environment:
      MY_ENV_VARIABLE: ${param:MY_ENV_VARIABLE}  

Then basing on the stage name that you pass during deployment, a correct value will be picked. In that example for prod the value of MY_ENV_VARIABLE will be different. If non-standard stage will be provided, then it will fallback to default value.