[DOCS-11944] Add Node.js examples and non-JSON log correlation for OTel traces

content/en/tracing/other_telemetry/connect_logs_and_traces/opentelemetry.md

@@ -39,7 +39,7 @@
 
 ### 1. Inject trace context into your logs
 
-The following examples for Go and Java use logging bridges. These bridges intercept logs from common logging libraries (such as `zap` and `Logback`), convert them into the OpenTelemetry log data model, and forward them to the OpenTelemetry SDK. This process automatically enriches the logs with the active trace context.
+The following examples use logging bridges or auto-instrumentation. These tools intercept logs from common logging libraries (such as `zap`, `Logback`, and `Winston`), convert them into the OpenTelemetry log data model, and forward them to the OpenTelemetry SDK. This process automatically enriches the logs with the active trace context.
 
 For complete, working applications, see the [Datadog OpenTelemetry Examples repository][2].
 
@@ -88,6 +88,51 @@
 
 [200]: https://github.com/DataDog/opentelemetry-examples/blob/main/apps/rest-services/java/calendar/src/main/resources/logback.xml
 
+{{% /tab %}}
+
+{{% tab "Node.js" %}}
+
+For Node.js, use the `@opentelemetry/instrumentation-winston` package with [Winston][300] to automatically inject trace context into your logs. Install the required packages:
+
+```shell
+npm install winston @opentelemetry/instrumentation-winston
+```
+
+Then, register the Winston instrumentation as part of your OpenTelemetry SDK setup:
+
+```javascript
+const { WinstonInstrumentation } = require('@opentelemetry/instrumentation-winston');
+const { NodeSDK } = require('@opentelemetry/sdk-node');
+
+const sdk = new NodeSDK({
+  instrumentations: [
+    new WinstonInstrumentation(),
+    // ... other instrumentations
+  ],
+});
+sdk.start();
+```
+
+After the instrumentation is registered, any Winston logger automatically includes `trace_id`, `span_id`, and `trace_flags` fields when a log is emitted within an active trace:
+
+```javascript
+const winston = require('winston');
+
+const logger = winston.createLogger({
+  level: 'info',
+  format: winston.format.json(),
+  transports: [new winston.transports.Console()],
+});
+
+// Logs emitted within a traced context automatically include trace_id and span_id
+logger.info('Processing user request');
+```
+
+The same approach works with [Pino][301] using the `@opentelemetry/instrumentation-pino` package.
+
+[300]: https://github.com/winstonjs/winston
+[301]: https://github.com/pinojs/pino
+
 {{% /tab %}}
 {{< /tabs >}}
 
@@ -141,25 +186,27 @@
          exporters: [datadog]
    ```
 
-#### Scrape logs from files 
+#### Scrape logs from files
 
 This approach is useful if you have a requirement to keep local log files for compliance or other tooling.
 
-For Datadog to correlate your logs and traces, your JSON log files must contain specific fields formatted correctly:
+For Datadog to correlate your logs and traces, your log files must contain specific fields formatted correctly:
 - `trace_id`: The ID of the trace. It must be a 32-character lowercase hexadecimal string.
-- `span_id`: The ID of the span. It must be a 16-character lowercase hexadecimal string.  
+- `span_id`: The ID of the span. It must be a 16-character lowercase hexadecimal string.
 
 The OpenTelemetry SDK typically provides these in a raw format (such as an integer or byte array), which must be formatted into hexadecimal strings without any <code>0x</code> prefix.
 
+##### JSON logs
+
 1. **Configure your Application to Output JSON Logs**: Use a standard logging library to write logs as JSON to a file or `stdout`. The following Python example uses the standard `logging` library.
-2. **Manually Inject Trace Context**: In your application code, retrieve the current span context and add the `trace_id` and `span_id` to your log records. The following Python example shows how to create a custom logging.Filter to do this automatically:
+2. **Manually Inject Trace Context**: In your application code, retrieve the current span context and add the `trace_id` and `span_id` to your log records. The following Python example shows how to create a custom `logging.Filter` to do this automatically:
 
    ```python
    import logging
    import sys
    from opentelemetry import trace
    from pythonjsonlogger import jsonlogger
-   
+
    # 1. Create a filter to inject trace context
    class TraceContextFilter(logging.Filter):
        def filter(self, record):
@@ -169,25 +216,25 @@
                record.trace_id = f'{span_context.trace_id:032x}'
                record.span_id = f'{span_context.span_id:016x}'
            return True
-   
+
    # 2. Configure a JSON logger
    logger = logging.getLogger("my-json-logger")
    logger.setLevel(logging.DEBUG)
-   
+
    # 3. Add the filter to the logger
    logger.addFilter(TraceContextFilter())
-   
+
    handler = logging.StreamHandler(sys.stdout)
    formatter = jsonlogger.JsonFormatter(
        '%(asctime)s %(name)s %(levelname)s %(message)s %(trace_id)s %(span_id)s'
    )
    handler.setFormatter(formatter)
    logger.addHandler(handler)
-   
+
    # Logs will now contain the trace_id and span_id
    logger.info("Processing user request with trace context.")
    ```
-   
+
 3. **Configure the Collector to Scrape Log Files**: In your Collector's `config.yaml`, enable the `filelog` receiver. Configure it to find your log files and parse them as JSON.
    ```yaml
    receivers:
@@ -197,14 +244,77 @@
          - type: json_parser
            # The timestamp and severity fields should match your JSON output
            timestamp:
-             parse_from: attributes.asctime 
+             parse_from: attributes.asctime
              layout: '%Y-%m-%d %H:%M:%S,%f'
            severity:
              parse_from: attributes.levelname
    # ... your logs pipeline ...
    ```
 
-This manual approach gives you full control over the log format, ensuring it is clean and easily parsable by the Collector or Datadog Agent.
+##### Non-JSON logs
+
+If your application outputs logs in a plain text or key-value format instead of JSON, you can still correlate them with traces. You need to manually inject the trace context into the log string and configure the Collector to extract it using a `regex_parser`.
+
+The following Node.js example uses Winston with a custom formatter to inject `trace_id` and `span_id` into a plain text log line:
+
+```javascript
+const { trace, context } = require('@opentelemetry/api');
+const winston = require('winston');
+
+// Custom format that injects trace context into plain text logs
+const traceFormat = winston.format((info) => {
+  const span = trace.getSpan(context.active());
+  if (span) {
+    const spanContext = span.spanContext();
+    info.trace_id = spanContext.traceId;
+    info.span_id = spanContext.spanId;
+  }
+  return info;
+});
+
+const logger = winston.createLogger({
+  level: 'info',
+  format: winston.format.combine(
+    traceFormat(),
+    winston.format.timestamp(),
+    winston.format.printf(({ timestamp, level, message, trace_id, span_id }) => {
+      return `${timestamp} ${level} trace_id=${trace_id || '0'} span_id=${span_id || '0'} ${message}`;
+    })
+  ),
+  transports: [
+    new winston.transports.File({ filename: '/var/log/my-app/app.log' })
+  ],
+});
+
+// Output: 2025-01-15T12:00:00.000Z info trace_id=4bf92f3577b34da6a3ce929d0e0e4736 span_id=00f067aa0ba902b7 Processing request
+logger.info('Processing request');
+```
+
+Then, configure the Collector's `filelog` receiver with a `regex_parser` to extract the trace context from the plain text log lines:
+
+```yaml
+receivers:
+  filelog:
+    include: [ /var/log/my-app/*.log ]
+    operators:
+      - type: regex_parser
+        regex: '^(?P<timestamp>\S+) (?P<severity>\S+) trace_id=(?P<trace_id>[a-f0-9]+) span_id=(?P<span_id>[a-f0-9]+) (?P<body>.*)$'
+        timestamp:
+          parse_from: attributes.timestamp
+          layout: '%Y-%m-%dT%H:%M:%S.%fZ'
+        severity:
+          parse_from: attributes.severity
+        trace:
+          trace_id:
+            parse_from: attributes.trace_id
+          span_id:
+            parse_from: attributes.span_id
+# ... your logs pipeline ...
+```
+
+This approach works with any logging library or language. The key requirements are:
+- Include `trace_id` and `span_id` as parseable fields in your log output.
+- Configure the Collector's `regex_parser` to match your log format and extract the trace context fields.
 
 #### Collect logs using the Datadog Agent