Session start and end events (#1091)

Co-authored-by: Joao Grassi <[email protected]>
Co-authored-by: Liudmila Molkova <[email protected]>

.chloggen/session_start_end_event.yaml

@@ -0,0 +1,22 @@
+# Use this changelog template to create an entry for release notes.
+#
+# If your change doesn't affect end users you should instead start
+# your pull request title with [chore] or use the "Skip Changelog" label.
+
+# One of 'breaking', 'deprecation', 'new_component', 'enhancement', 'bug_fix'
+change_type: 'enhancement'
+
+# The name of the area of concern in the attributes-registry, (e.g. http, cloud, db)
+component: 'session'
+
+# A brief description of the change. Surround your text with quotes ("") if it needs to start with a backtick (`).
+note: Add new experimental `session.start` and `session.end` events
+
+# Mandatory: One or more tracking issues related to the change. You can use the PR number here if no issue exists.
+# The values here must be integers.
+issues: [1091]
+
+# (Optional) One or more lines of additional information to render under the primary note.
+# These lines will be padded with 2 spaces and then inserted directly into the document.
+# Use pipe (|) for multiline entries.
+subtext:

docs/general/session.md

@@ -13,7 +13,7 @@ the Logs, Events, and Spans generated during the Session's lifecycle.
 
 When a session reaches end of life, typically due to user inactivity or session timeout, a new session identifier
 will be assigned. The previous session identifier may be provided by the instrumentation so that telemetry
-backends can link the two sessions.
+backends can link the two sessions (see [Session Start Event](#session-start-event) below).
 
 ## Attributes
 
@@ -35,4 +35,41 @@ backends can link the two sessions.
 <!-- END AUTOGENERATED TEXT -->
 <!-- endsemconv -->
 
+## Session Events
+
+### Session Start Event
+
+![Experimental](https://img.shields.io/badge/-experimental-blue)
+
+`event.name` MUST be`session.start`
+
+For instrumentation that tracks user behavior during user sessions, a `session.start` event MUST be emitted
+every time a session is created. When a new session is created as a continuation of a prior session,
+the `session.previous_id` SHOULD be included in the event. The values of `session.id` and `session.previous_id`
+MUST be different.
+
+When the `session.start` event contains both `session.id` and `session.previous_id` fields, the event then implies
+that the previous session has ended. If the session ID in `session.previous_id` has not yet ended via explicit
+`session.end` event, then the consumer SHOULD treat this continuation event as semantically equivalent to
+`session.end(session.previous_id)` and `session.start(session.id)`.
+
+| Body field                                                    | Type   | Description                                          | [Requirement Level](https://opentelemetry.io/docs/specs/semconv/general/attribute-requirement-level/) | Stability                                                        |
+|---------------------------------------------------------------|--------|------------------------------------------------------|-------------------------------------------------------------------------------------------------------|------------------------------------------------------------------|
+| [`session.id`](/docs/attributes-registry/session.md)          | string | The ID of the new session being started.             | `Required`                                                                                            | ![Experimental](https://img.shields.io/badge/-experimental-blue) |
+| [`session.previous_id`](/docs/attributes-registry/session.md) | string | The previous `session.id` for this user, when known. | `Conditionally Required`                                                                              | ![Experimental](https://img.shields.io/badge/-experimental-blue) |
+
+### Session End Event
+
+![Experimental](https://img.shields.io/badge/-experimental-blue)
+
+`event.name` MUST be `session.end`
+
+For instrumentation that tracks user behavior during user sessions, a `session.end` event SHOULD be emitted
+every time a session ends. When a session ends and continues as a new session, this event SHOULD be
+emitted prior to the `session.start` event.
+
+| Body field                                                    | Type   | Description                            | [Requirement Level](https://opentelemetry.io/docs/specs/semconv/general/attribute-requirement-level/) | Stability                                                        |
+|---------------------------------------------------------------|--------|----------------------------------------|--------------------------|------------------------------------------------------------------|
+| [`session.id`](/docs/attributes-registry/session.md)          | string | The ID of the new session being ended. | `Required`                                                | ![Experimental](https://img.shields.io/badge/-experimental-blue) |
+
 [DocumentStatus]: https://opentelemetry.io/docs/specs/otel/document-status