All of the labels attached to the container whose logs are being collected should be added on to the logs. For example, if logs are being collected for container foo with the labels env=prod and service=backend, those labels (env=prod, service=backend) should be attached such that someone querying logs later can ask for all logs with those labels to easily aggregate across containers.

IIRC both elasticsearch and Google Cloud Logging support arbitrary labels, so the only work needed should be getting the container's labels into Fluentd and attaching them.

cc @satnam6502