Get an Engine instance assuming some sensible defaults.

This uses the environment variable GOOGLE_CLOUD_PROJECT for the Engine project_id, unless set explicitly. By using an environment variable, you can avoid hard-coding the project_id in shared code.

If the environment variables are set, but incorrect, an authentication failure will occur when attempting to run jobs on the engine.

project_id If set overrides the project id obtained from the environment variable GOOGLE_CLOUD_PROJECT.

The Engine instance.

EnvironmentError If the environment variable GOOGLE_CLOUD_PROJECT is not set.