| project | string | no | no | The Google Cloud project to write to. |
| credentials_json | string | no | no | JSON credentials for authenticating with GCP. |
| topic | expression | no | no | The topic to publish to. This field supports interpolation functions. |
| endpoint | string | yes | no | An optional endpoint to override the default of pubsub.googleapis.com:443. This can be used to connect to a region specific pubsub endpoint. For a list of valid values, see this document. |
| ordering_key | expression | yes | no | The ordering key to use for publishing messages. This field supports interpolation functions. |
| publish_timeout | string | yes | no | The maximum duration to wait for a message to be published before timing out. The value defaults to 1m. |
| metadata | metadata | yes | no | Specify criteria for which metadata values are attached to objects as headers. |
| max_in_flight | int | yes | no | The maximum number of messages to have in flight at any given time. The value defaults to 64. |
