Make filebeat pub/sub input work with Google pub/sub emulator

[jbogp]

Hello

Describe the enhancement:
Google makes a pubsub emulator available for local development, https://cloud.google.com/pubsub/docs/emulator
I've tried to make the pub/sub filebeat input work with it by exporting the environment variables PUBSUB_EMULATOR_HOST and PUBSUB_PROJECT_ID inside the container running filebeat (following the emulator documentation linked above), unfortunately filebeat still crashes with a "missing API key" error which seems to indicate the pub/sub library used doesn't take into account the possibility of an emulator

Describe a specific use case for the enhancement or feature:
This would be NTH to be able to develop the pipeline entirely locally without relying on a real pub/sub instance. Also the emulator is an official Google product so it's maintained and here to stay.

[andrewkroh]

The emulator is used by the googlepubsub input's integration tests so it works with it. In order to satisfy Filebeat's config validation try setting the credential_file option to a dummy value like the tests do and see if that works.

beats/x-pack/filebeat/input/googlepubsub/pubsub_test.go

Line 205 in 56103a3

"credentials_file": "NONE FOR EMULATOR TESTING",

[jbogp]

Thank you that worked.