JSON lines

The default sink writes each entry as one JSON line to stdout. GKE, Cloud Run and a GCE instance with the Cloud Logging agent parse structured JSON from stdout, so the layer only has to serialise each event: the keys above map onto Cloud Logging’s LogEntry fields.

let log_layer = GcpCloudLoggingLayerBuilder::new(google_project_id).build()?;

with_json_writer takes any tracing_subscriber::fmt::MakeWriter in place of stdout. Each line is written with a single write_all, so concurrent events do not interleave partial lines on a shared writer. I/O errors are ignored: a full disk or a broken pipe does not turn into a panic.

On a host without the agent the lines only print. Use the Cloud Logging API or OTLP sink there.

Full example available here.