Comparison with the OpenTelemetry tracing bridge

opentelemetry-appender-tracing is the stock bridge from tracing events to OpenTelemetry log records. Sent to the Telemetry API, its records and those of the OTLP sink reach Cloud Logging differently, because the sink maps the conventional fields onto typed LogEntry fields before sending.

The same event, as the bridge sends it, trimmed:

{
  "logName": "projects/my-project/logs/event%20src%2Fbin%2Fbridge.rs%3A26",
  "severity": "INFO",
  "textPayload": "bridge probe checkout request received",
  "labels": {
    "http_request.request_method": "POST",
    "http_request.request_url": "https://example.test/orders/order-42/checkout",
    "http_request.status": "200",
    "labels.tenant": "acme"
  },
  "trace": "b5c11cf3e9cb0d1710251307eaaed739",
  "spanId": "49f19eb158811ff5",
  "traceSampled": true
}

and as the OTLP sink sends it, trimmed:

{
  "logName": "projects/my-project/logs/gcloud-observability-example",
  "severity": "INFO",
  "jsonPayload": {
    "message": "checkout request received",
    "target": "logging_otlp"
  },
  "httpRequest": {
    "requestMethod": "POST",
    "requestUrl": "https://example.test/orders/order-42/checkout",
    "status": 200,
    "latency": "0.125s"
  },
  "labels": {
    "gcp.log.name": "gcloud-observability-example",
    "tenant": "acme"
  },
  "sourceLocation": { "file": "examples/logging/otlp.rs", "line": "78" },
  "insertId": "1noy1uke8wh62",
  "trace": "b3f6d198940b478f16da57f0c19e491b",
  "spanId": "cbdd640d48c893e0",
  "traceSampled": true
}

The differences:

• the bridge writes a textPayload with the message only; the sink writes a jsonPayload with the message, the target and every other field with its type;
• the bridge sends every field as a string label, and the http_request.* fields stay labels; the sink fills the typed httpRequest and sourceLocation, and an operation and an insertId when the event has them;
• the bridge’s logName is made per call site; the sink writes every entry to the one log named by its LogId;
• both entries carry the trace and span of the enclosing span.