How to mix env variables with output variables in the environment declaration - serverless-framework

Question

So I have a env.yml file which lets me have a different variables for each stage:
provider:
name: aws
environment: ${file(env.yml):${opt:stage}}
I also need to share some output variables to Lambda which are declared like so:
Outputs:
UserPoolId:
Value:
Ref: QNABUserPool
Export:
Name: ${self:provider.stage}-UserPoolId
UserPoolClientId:
Value:
Ref: QNABUserPoolClient
Export:
Name: ${self:provider.stage}-UserPoolClientId
I've seen I can do this by adding this to my provider but this conflicts with my env.yml
environment:
COGNITO_USER_POOL_ID: ${cf:${self:service}-${self:provider.stage}.UserPoolId}
COGNITO_USER_POOL_CLIENT_ID: ${cf:${self:service}-${self:provider.stage}.UserPoolClientId}
I tried putting these into the env.yml but that didn't work:
Trying to request a non exported variable from CloudFormation. Stack name: "XXXX-alpha" Requested variable: "UserPoolId".
I tried using custom instead of environment and it deployed but the Lambda functions no longer had access to the variables.
So how can I mix these two together?
Thank you so much!

Answer 1

You can reference the Output values from your current service using the Fn::ImportValue function.
The serverless system adds sls-[service_name] to the variable but you can find them in the Outputs area of the CloudFormation Stack.
Navigate to CloudFormation --> Stacks --> [select your service] --> Outputs (tab). From there you'll see a column called Exports name.
Use that Exports name and use that for the import.
e.g. you have a WebSocket service and you need the service endpoint. If you look in the tab it will have an export ~ sls-wss-[your_service_name]-[stage]-ServiceEndpointWebsocket. Thus, you can import that into an environment variable:
Environment:
Variables:
ENDPOINT:
Fn::ImportValue: sls-wss-[your_service_name]-${opt:stage}-ServiceEndpointWebsocket