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docs: Documentation update for OpenTelemetry and tracing #1657

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19 changes: 8 additions & 11 deletions .readme-partials.yaml
Original file line number Diff line number Diff line change
Expand Up @@ -227,20 +227,17 @@ custom_content: |
<artifactId>google-cloud-logging-servlet-initializer</artifactId>
</dependency>
```
#### Population of log entrys' trace/span Id
#### Population of Log Entrys' Trace/Span ID
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Do we want to title this "Automatic Trace/Span ID Extraction" to be consistent with the language used in other client libraries?

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Hi Kevin, Java-logging is a bit special here. We don't have auto extraction for Http headers unless it's through manual setting or using servlet-initializer.

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Cloud Logging libraries use [trace fields within LogEntry](https://cloud.google.com/logging/docs/reference/v2/rest/v2/LogEntry#FIELDS.trace) to capture trace contexts, which enables the [correlation of logs and traces](https://cloud.google.com/logging/docs/view/correlate-logs), and distributed tracing troubleshooting.
These tracing fields including [trace](https://cloud.google.com/logging/docs/reference/v2/rest/v2/LogEntry#FIELDS.trace), [spanId](https://cloud.google.com/logging/docs/reference/v2/rest/v2/LogEntry#FIELDS.span_id), and [traceSampled](https://cloud.google.com/logging/docs/reference/v2/rest/v2/LogEntry#FIELDS.trace_sampled) define the trace context for a `LogEntry`.
These tracing fields, including [trace](https://cloud.google.com/logging/docs/reference/v2/rest/v2/LogEntry#FIELDS.trace), [spanId](https://cloud.google.com/logging/docs/reference/v2/rest/v2/LogEntry#FIELDS.span_id), and [traceSampled](https://cloud.google.com/logging/docs/reference/v2/rest/v2/LogEntry#FIELDS.trace_sampled), define the trace context for a `LogEntry`.

The library provides three methods to update trace/span Id:
* Manually set trace/span Id
The trace and span Ids can be set directly using `setTraceId()` and `setSpanId()` methods provided by `Context.Builder`. Alternatively it can also be parsed from the [W3C tracing context header](https://www.w3.org/TR/trace-context) using `loadW3CTraceParentContext()` or from the [Google Cloud tracing context header](https://cloud.google.com/trace/docs/trace-context#legacy-http-header) using `loadCloudTraceContext()`.
Tracing information set using this method will take precedence over other methods below.
Tracing information set manually takes precedence over information set by the following methods:

* Auto-populate trace/span Id from OpenTelemetry context
If you are using OpenTelemetry and there is an active span in the OpenTelemetry Context, that log entry will automatically have the `trace`, `span_id`, and `trace_sampled` fields populated from that span. More information about OpenTelemetry can be found [here](https://opentelemetry.io/docs/languages/java/).
* Auto-populate Trace/Span ID from OpenTelemetry Context
If you are using OpenTelemetry and there is an active span in the OpenTelemetry Context, the `trace`, `span_id`, and `trace_sampled` fields in the log entry are populated from the active span. More information about OpenTelemetry can be found [here](https://opentelemetry.io/docs/languages/java/).

* Use [servlet initializer](https://github.com/googleapis/java-logging-servlet-initializer) to populate trace/span Id from HTTP headers
If trace/span Id is not manually set or auto-populated from OpenTelemetry context, you can use [servlet initializer](https://github.com/googleapis/java-logging-servlet-initializer) package to populate trace/span Id from HTTP headers.
This package filters all servlet requests to automatically capture the execution context of the servlet request and store it using ContextHandler class. Http request and trace/span Id information will be populated from the stored Context class instances.
* Use the [servlet initializer](https://github.com/googleapis/java-logging-servlet-initializer) to Populate Trace/Span ID from HTTP Headers
If trace/span Id are not manually set or auto-populated from OpenTelemetry context, you can use the [servlet initializer](https://github.com/googleapis/java-logging-servlet-initializer) to populate trace/span Id from HTTP headers.
This package filters all servlet requests to automatically capture the execution context of the servlet request and stores it by using ContextHandler class. Http request and trace/span Id information are populated from the stored Context class instances.
Using this method, trace/span Id can be automatically populated from either the [W3C Traceparent](https://www.w3.org/TR/trace-context) or [X-Cloud-Trace-Context](https://cloud.google.com/trace/docs/trace-context#legacy-http-header) headers.

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