Google Cloud observability for Rust

Formerly opentelemetry-gcloud-trace, see Migrating from 0.30.

The library sends what a Rust service emits through tracing and OpenTelemetry to Google Cloud:

• Cloud Logging: a tracing-subscriber layer that turns every event into a structured log entry, correlated with the trace and span that emitted it, so the Google Cloud console shows each log line under its trace;
• three log sinks: JSON lines on stdout for GKE, Cloud Run and hosts with the Cloud Logging agent, the Cloud Logging API, and OTLP;
• Error Reporting: errors logged with the code location, the source() chain and a backtrace, and panics, in the format Error Reporting groups;
• Cloud Trace: OpenTelemetry span exporters for the Telemetry API and for the Cloud Trace API v2;
• Authentication for any OTLP exporter, metrics included, with Application Default Credentials refreshed in the background.

Terms

OTLP is the OpenTelemetry protocol, the wire format OpenTelemetry SDKs send traces, metrics and logs in. The Telemetry API (telemetry.googleapis.com) is the Google Cloud endpoint that takes OTLP for all three signals; see Telemetry API overview. Application Default Credentials (ADC) is the way Google client libraries find credentials: an environment variable, a local file written by gcloud, or the metadata server of the host.

How the pieces fit

• A span is created by tracing macros or by the OpenTelemetry API. The tracing-opentelemetry layer turns tracing spans into OpenTelemetry spans, and a tracer provider hands finished spans to an exporter: otlp for the Telemetry API, or trace-api for the Cloud Trace API.
• A tracing event passes through the logging layer, which builds one log entry and gives it to the sink chosen when the layer was built.
• The logging layer reads the trace and span ids that the tracing-opentelemetry layer attached, so the entry and the span are linked in the console. The tracing-opentelemetry layer is therefore registered first, see The logging layer.
• The exporters, the Cloud Logging API sink and any OTLP exporter built elsewhere authenticate through the same ADC, see Authentication.

Neither exporter is enabled by default, see Feature flags. To start using the library, see Quick start.