Events and logs api (open-telemetry#2676)

This PR is a follow up to the OTEP [Events and Logs API](https://github.com/open-telemetry/oteps/blob/main/text/0202-events-and-logs-api.md). It describes the specification for an Events and Logs API and also defines semantic conventions for attributes to be used for Events that are represented using Log Records.

For non-trivial changes, follow the [change proposal
process](../CONTRIBUTING.md#proposing-a-change) and link to the related issue(s)
and/or [OTEP(s)](https://github.com/open-telemetry/oteps), update the
[`CHANGELOG.md`](../CHANGELOG.md), and also be sure to update
[`spec-compliance-matrix.md`](../spec-compliance-matrix.md) if necessary.


Related [OTEP(s)](https://github.com/open-telemetry/oteps) #

[Events and Logs API](https://github.com/open-telemetry/oteps/blob/main/text/0202-events-and-logs-api.md)

CHANGELOG.md

@@ -31,6 +31,8 @@ release.
 
 - Update log SDK to allow log processors to mutate log records
   ([#2681](https://github.com/open-telemetry/opentelemetry-specification/pull/2681)).
+- Add experimental Events and Logs API specification
+  ([#2676](https://github.com/open-telemetry/opentelemetry-specification/pull/2676))
 
 ### Resource
 

semantic_conventions/logs/events.yaml

@@ -0,0 +1,32 @@
+groups:
+  - id: event
+    prefix: event
+    brief: >
+        This document defines attributes for Events represented using Log Records.
+    attributes:
+      - id: name
+        type: string
+        requirement_level: required
+        brief: >
+          The name identifies the event.
+        examples: ['click', 'exception']
+      - id: domain
+        brief: >
+          The domain identifies the context in which an event happened. An event name is unique only within a domain.
+        type:
+          allow_custom_values: true
+          members:
+            - id: browser
+              value: 'browser'
+              brief: 'Events from browser apps'
+            - id: device
+              value: 'device'
+              brief: 'Events from mobile apps'
+            - id: k8s
+              value: 'k8s'
+              brief: 'Events from Kubernetes'
+        requirement_level: required
+        note: |
+          An `event.name` is supposed to be unique only in the context of an
+          `event.domain`, so this allows for two events in different domains to
+          have same `event.name`, yet be unrelated events.

specification/logs/api.md

@@ -0,0 +1,145 @@
+# Events and Logs API Interface
+
+**Status**: [Experimental](../document-status.md)
+
+<details>
+<summary>Table of Contents</summary>
+
+<!-- Re-generate TOC with `markdown-toc --no-first-h1 -i` -->
+
+<!-- toc -->
+
+- [Data Model](#data-model)
+- [LoggerProvider](#loggerprovider)
+  * [LoggerProvider operations](#loggerprovider-operations)
+    + [Get a Logger](#get-a-logger)
+- [Logger](#logger)
+  * [Logger operations](#logger-operations)
+
+<!-- tocstop -->
+
+</details>
+
+The Events and Logs API consist of these main classes:
+
+* LoggerProvider is the entry point of the API. It provides access to Loggers.
+* Logger is the class responsible for creating events and logs using Log records.
+
+LoggerProvider/Logger are analogous to TracerProvider/Tracer.
+
+```mermaid
+graph TD
+    A[LoggerProvider] -->|Get| B(Logger)
+    B --> C(Event)
+    B --> D(Log)
+```
+
+## Data Model
+
+The API creates Events and Logs using the `LogRecord` data model. See `LogRecord` [data model](data-model.md) for the list of fields.
+
+## LoggerProvider
+
+`Logger`s can be accessed with a `LoggerProvider`.
+
+In implementations of the API, the LoggerProvider is expected to be the stateful
+object that holds any configuration.
+
+Normally, the LoggerProvider is expected to be accessed from a central place.
+Thus, the API SHOULD provide a way to set/register and access a global default
+LoggerProvider.
+
+Notwithstanding any global LoggerProvider, some applications may want to or have
+to use multiple LoggerProvider instances, e.g. to have different configuration
+(like LogProcessors) for each (and consequently for the Loggers obtained
+from them), or because it's easier with dependency injection frameworks. Thus,
+implementations of LoggerProvider SHOULD allow creating an arbitrary number of
+instances.
+
+### LoggerProvider operations
+
+The LoggerProvider MUST provide the following functions:
+
+* Get a Logger
+
+#### Get a Logger
+
+This API MUST accept the following parameters:
+
+- `name` (required): This name SHOULD uniquely identify the [instrumentation scope](../glossary.md#instrumentation-scope),
+such as the [instrumentation library](../glossary.md#instrumentation-library)
+(e.g. `io.opentelemetry.contrib.mongodb`), package, module or class name.
+If an application or library has built-in OpenTelemetry instrumentation, both
+[Instrumented library](../glossary.md#instrumented-library) and
+[Instrumentation library](../glossary.md#instrumentation-library) may refer to
+the same library. In that scenario, the `name` denotes a module name or component
+name within that library or application. In case an invalid name
+(null or empty string) is specified, a working Logger implementation MUST be
+returned as a fallback rather than returning null or throwing an exception, its
+`name` property SHOULD be set to an empty string, and a message reporting that
+the specified value is invalid SHOULD be logged. A library implementing the
+OpenTelemetry API may also ignore this name and return a default instance for
+all calls, if it does not support "named" functionality (e.g. an implementation
+which is not even observability-related). A LoggerProvider could also return a
+no-op Logger here if application owners configure the SDK to suppress telemetry
+produced by this library.
+- `version` (optional): Specifies the version of the instrumentation scope if
+the scope has a version (e.g. a library version). Example value: 1.0.0.
+- `schema_url` (optional): Specifies the Schema URL that should be recorded in
+the emitted telemetry.
+- `event_domain` (optional): Specifies the domain for the events created, which
+should be added as `event.domain` attribute of the instrumentation scope.
+- `include_trace_context` (optional): Specifies whether the Trace Context should
+automatically be passed on to the events and logs created by the Logger. This
+SHOULD be true by default.
+- `attributes` (optional): Specifies the instrumentation scope attributes to
+associate with emitted telemetry.
+
+Implementations MUST return different `Logger` instances when called repeatedly
+with different values of parameters. Note that always returning a new `Logger`
+instance is a valid implementation. The only exception to this rule is the no-op
+`Logger`: implementations MAY return the same instance regardless of parameter
+values.
+
+Implementations MUST NOT require users to repeatedly obtain an Logger again with
+the same name+version+schema_url+event_domain+include_trace_context+attributes
+to pick up configuration changes. This can be achieved either by allowing to
+work with an outdated configuration or by ensuring that new configuration
+applies also to previously returned Loggers.
+
+Note: This could, for example, be implemented by storing any mutable
+configuration in the `LoggerProvider` and having `Logger` implementation objects
+have a reference to the `LoggerProvider` from which they were obtained.
+If configuration must be stored per-Logger (such as disabling a certain `Logger`),
+the `Logger` could, for example, do a look-up with its name+version+schema_url+event_domain+include_trace_context+attributes
+in a map in the `LoggerProvider`, or the `LoggerProvider` could maintain a registry
+of all returned `Logger`s and actively update their configuration if it changes.
+
+The effect of associating a Schema URL with a `Logger` MUST be that the telemetry
+emitted using the `Logger` will be associated with the Schema URL, provided that
+the emitted data format is capable of representing such association.
+
+## Logger
+
+The `Logger` is responsible for creating Events and Logs.
+
+Note that `Logger`s should not be responsible for configuration. This should be
+the responsibility of the `LoggerProvider` instead.
+
+### Logger operations
+
+The Logger MUST provide functions to:
+
+- Create a `LogRecord`, representing an `Event` and emit it to the processing
+pipeline.
+  - The API MUST accept an event name as a parameter. The event name provided
+  should be recorded as an attribute with key `event.name`. Care MUST be taken
+  by the implementation to not override or delete this attribute while the
+  `Event` is created to preserve its identity.
+  - Events require the `event.domain` attribute. The API MUST not allow creating
+  an event if the Logger instance doesn't have `event.domain` scope attribute.
+  - This function MAY be named `logEvent`.
+- Create a `LogRecord` and emit it to the processing pipeline.
+  - This function MAY be named `logRecord`.
+  - This API is intended for use by Log Appenders, and SHOULD not be used by end
+  users or other instrumentation.

specification/logs/semantic_conventions/README.md

@@ -6,6 +6,10 @@ The following semantic conventions for logs are defined:
 
 * [Log Media](media.md): Semantic attributes that may be used in describing the source of a log.
 
+The following semantic conventions for events are defined:
+
+* [Events](events.md): Semantic attributes that must be used to represent Events using log data model.
+
 Apart from semantic conventions for logs, [traces](../../trace/semantic_conventions/README.md), and [metrics](../../metrics/semantic_conventions/README.md),
 OpenTelemetry also defines the concept of overarching [Resources](../../resource/sdk.md) with their own
 [Resource Semantic Conventions](../../resource/semantic_conventions/README.md).

specification/logs/semantic_conventions/events.md

@@ -0,0 +1,27 @@
+# Semantic Convention for event attributes
+
+**Status**: [Experimental](../../document-status.md)
+
+This document describes the attributes of standalone Events that are represented
+by `LogRecord`s. All standalone Events have a name and a domain. The Event domain
+is a namespace for event names and is used as a mechanism to avoid conflicts of
+event names.
+
+<!-- semconv event -->
+| Attribute  | Type | Description  | Examples  | Requirement Level |
+|---|---|---|---|---|
+| `event.name` | string | The name identifies the event. | `click`; `exception` | Required |
+| `event.domain` | string | The domain identifies the context in which an event happened. An event name is unique only within a domain. [1] | `browser` | Required |
+
+**[1]:** An `event.name` is supposed to be unique only in the context of an
+`event.domain`, so this allows for two events in different domains to
+have same `event.name`, yet be unrelated events.
+
+`event.domain` has the following list of well-known values. If one of them applies, then the respective value MUST be used, otherwise a custom value MAY be used.
+
+| Value  | Description |
+|---|---|
+| `browser` | Events from browser apps |
+| `device` | Events from mobile apps |
+| `k8s` | Events from Kubernetes |
+<!-- endsemconv -->