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An OpenTelemetry logs bridge has to preserve what a source logging system meant—not just turn its output into bytes. The key work is mapping timestamps, severity, structured bodies, trace context, resource and scope correctly, then understanding how SDK limits and export lifecycle affect the resulting records.
What an OpenTelemetry logs bridge does
OpenTelemetry describes the Logs Bridge API as a way for logging-library authors to build appenders or bridges that translate existing logging systems into OpenTelemetry LogRecords. Application developers generally keep using their preferred logging library and configure an appender or bridge; OpenTelemetry documentation says, “The Logs Bridge API should not be called by application developers directly.” OpenTelemetry Logs Bridge API
That distinction matters: the bridge adapts the source library’s event model and context to OpenTelemetry’s model. It is not simply a formatter that copies a rendered line into a message field.
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What a bridge needs to map
An OpenTelemetry LogRecord has distinct fields for event time, observation time, trace context, severity, body, resource, instrumentation scope, attributes, and event name. Mapping choices determine which of those distinctions survive. OpenTelemetry Logs Data Model
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| LogRecord field or concept | What it represents | Bridge decision |
|---|---|---|
| Timestamp | When the source event occurred. | Use the source event time when available; do not silently treat bridge or collector receipt time as event time. |
| ObservedTimestamp | When the event was observed. | Keep observation time distinct from the event’s timestamp. |
| SeverityText | The source’s level label, such as its original textual severity. | Decide whether to preserve the source label, rather than assuming a numeric level is enough. |
| SeverityNumber | A normalized severity value used for ordering and comparison. | Map source levels deliberately; preserve the text label separately where supported. |
| Body | The event’s content, which can be structured AnyValue data or a rendered string. | Keep structured message data where possible instead of flattening it prematurely into text. |
| TraceId, SpanId, TraceFlags | Trace context associated with the log event. | Check how the source’s contextual logging data reaches the bridge and whether it is attached to the record. |
| Resource | The entity that generated the log; typically stable across records from that source. | Assign source identity at the resource level rather than repeating it as per-event detail. |
| InstrumentationScope | The instrumentation that emitted the record. | Keep emitting instrumentation distinct from the entity described by Resource. |
| Attributes | Event-specific details that can vary between occurrences. | Map key-value context here when it describes an individual event, while accounting for SDK limits. |
| EventName | A distinct event name where one is supplied. | Determine whether the source has an event identity worth preserving separately from its body. |
Keep metadata in the right place
Resource, InstrumentationScope, and Attributes are not interchangeable metadata buckets. Resource describes the log-producing entity and is generally stable; attributes describe a particular event; scope identifies the instrumentation that emitted it. Collapsing them into one generic map can make downstream queries less consistent and obscure whether a value belongs to a service, an instrumentation component, or one occurrence.
Preserve structure and context, not only rendered text
A rendered line is convenient for display, but it can discard the source’s structured body and key-value context. Likewise, a log message may be useful without its trace identifiers, but it is less useful for trace-linked investigation. A bridge should be assessed on whether it carries those data in the corresponding record fields, not just whether the output looks readable.
Why SDK limits and lifecycle behavior matter
Correct field mapping is only part of the work. The SDK needs access to the Resource and InstrumentationScope associated with a record. It also applies attribute limits, which can cause fields to be discarded. The SDK specification says counts of limit-driven discards must be available for exporters to report and recommends a user-visible message when an attribute is discarded. OpenTelemetry Logs SDK
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How to evaluate a bridge for your logging system
Inspect the specific bridge and version you plan to use. Documentation for one package is evidence about that package, not a guarantee about bridges for other languages or frameworks.
- Framework coverage: Does it bridge the logging API and version used by your application?
- Timestamp handling: Does it preserve source event time and distinguish it from observation time?
- Trace context: Does contextual logging data become TraceId, SpanId, and TraceFlags where available?
- Severity: How are source levels mapped to SeverityNumber, and is the original label retained in SeverityText?
- Body structure: Does it preserve structured message data or render everything as text?
- Resource and scope: Where are source identity and emitting instrumentation assigned?
- Limits and loss: What happens to attributes when SDK limits apply, and can exporters report discarded counts?
- Lifecycle and export: How does the bridge feed SDK processing and exporter behavior in the application?
A narrow example: the Go logr bridge
The Go otellogr package documents a bridge from logr.LogSink to OpenTelemetry. Its package documentation states that it does not set SeverityText and that context in KeyAndValues is propagated to the OpenTelemetry log record. otellogr package documentation
This example shows why it is useful to inspect mappings field by field: propagation of contextual key-value data does not, by itself, establish that source severity text is preserved. It describes this package only; other bridges may make different choices.
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1Repair Windows errors before they cause bigger problems2Scan for outdated or missing drivers - takes under a minute3Clear out junk files and repair common Windows errorsWhy a log bridge may lose context or severity
- Severity text is absent: The implementation may map a source level to a number without setting its original label, as the documented
otellogrbehavior illustrates. - Trace context is missing: Context attached to a logging call may not be propagated into the record’s trace fields, or the source API may not provide it in the form the bridge expects.
- Event details disappear: Structured body data or key-value context may be flattened, mapped to a different field, or discarded when attribute limits apply.
- Source identity is inconsistent: Resource, scope, and event attributes may be assigned as though they represented the same kind of metadata.
- Times are confusing: A record’s event timestamp and the time it was observed may be treated as one value, even though the data model distinguishes them.
When diagnosing a discrepancy, inspect the bridge’s mapping documentation and the emitted LogRecord fields, then check SDK limits and exporter-visible discard information. A readable exported message alone does not show whether the other record fields survived.
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