Yaml validation error on TaskDefinition preventing cloudformation from reaching completion

Question

I'm trying to create a cloudformation for a Task Definition but I keep running into validation errors on the command portion of the Task Definition. I've tried a few approaches and can't seem to get it right.

I've been following the documentation here.

Below are 2 of my main attempts and their respective errors:

Command: !Sub 
         - "--config config.yaml --env ${environment}"
         - { environment: !FindInMap [EnvironmentVariables, !Ref Environment, Environment] }
Environment] }

Error:

#/ContainerDefinitions/0/Command: expected type: JSONArray, found: String)

Command: !Sub 
      - [--config, config.yaml, --env, ${environment}]
      - { environment: !FindInMap [EnvironmentVariables, !Ref Environment, Environment] }

Template format error: YAML not well-formed.

Answer 1

There seems to be some issue with how !Sub interacts with a Yaml list but I'm not exactly sure what causes this to be the case.

However the below piece of Yaml managed to solve my problem.

Command:
        - --config 
        - config.yaml
        - --env 
        - !FindInMap [EnvironmentVariables, !Ref Environment, Environment]