TekTree Event Catalog

Version: 1.0.0 Last Updated: 2025-12-16 Status: Foundation (Pre-Implementation)

Document Purpose

This document serves as the complete catalog of domain events in the TekTree platform. It defines event schemas, producers, consumers, choreography patterns, versioning strategy, and retention policies.

Event Taxonomy

Events are organized by domain and follow a hierarchical naming convention: Format: {domain}.{aggregate}.{action} Examples:

user.registered
knowledge.question.posted
gamification.achievement.unlocked
payment.subscription.upgraded

Event Schema Standards

All events follow this base schema:

{
  "event_id": "evt_abc123xyz",
  "event_type": "user.registered",
  "event_version": "1.0.0",
  "timestamp": "2025-12-16T14:30:00Z",
  "trace_id": "trace_abc123",
  "correlation_id": "corr_xyz789",
  "source_service": "user-service",
  "producer_id": "user-svc-pod-1",
  "metadata": {
    "user_id": "usr_123",
    "ip_address": "203.0.113.42",
    "user_agent": "Mozilla/5.0..."
  },
  "payload": {
    // Event-specific data
  }
}

Required Fields:

event_id: Unique identifier (UUID v4)
event_type: Event type (dot notation)
event_version: Semantic version of event schema
timestamp: ISO 8601 UTC timestamp
source_service: Service that emitted the event
payload: Event-specific data

Optional Fields:

trace_id: Distributed tracing ID
correlation_id: Links related events
producer_id: Instance that produced event
metadata: Contextual information (user, IP, etc.)

1. User Domain Events

Event: `user.registered`

Version: 1.0.0 Producer: User Service Consumers: Gamification Service, Payment Service, Email Service Description: Emitted when a new user successfully completes registration. Schema:

{
  "event_type": "user.registered",
  "event_version": "1.0.0",
  "timestamp": "2025-12-16T14:30:00Z",
  "payload": {
    "user_id": "usr_abc123",
    "email": "user@example.com",
    "handle": "johndoe",
    "email_verified": false,
    "registration_source": "web",
    "referrer": "organic",
    "initial_tier": "free"
  }
}

Consumer Actions:

Gamification Service: Award +100 XP welcome bonus
Payment Service: Create free tier subscription
Email Service: Send welcome email + verification email

Event: `user.profile.updated`

Version: 1.0.0 Producer: User Service Consumers: Search Service, Cache Service Description: Emitted when user updates their profile information. Schema:

{
  "event_type": "user.profile.updated",
  "event_version": "1.0.0",
  "timestamp": "2025-12-16T14:35:00Z",
  "payload": {
    "user_id": "usr_abc123",
    "updated_fields": ["first_name", "bio", "avatar"],
    "old_values": {
      "first_name": "John",
      "bio": null,
      "avatar": null
    },
    "new_values": {
      "first_name": "Jonathan",
      "bio": "Software engineer passionate about...",
      "avatar": "https://cdn.tektree.com/avatars/usr_abc123.jpg"
    }
  }
}

Consumer Actions:

Search Service: Reindex user profile
Cache Service: Invalidate user profile cache

Event: `user.authenticated`

Version: 1.0.0 Producer: User Service Consumers: Analytics Service, Gamification Service (streak tracking) Description: Emitted when user successfully logs in. Schema:

{
  "event_type": "user.authenticated",
  "event_version": "1.0.0",
  "timestamp": "2025-12-16T15:00:00Z",
  "payload": {
    "user_id": "usr_abc123",
    "session_id": "sess_xyz789",
    "auth_method": "email_password",
    "ip_address": "203.0.113.42",
    "device_type": "desktop",
    "user_agent": "Mozilla/5.0...",
    "location": {
      "country": "US",
      "city": "San Francisco"
    }
  }
}

Consumer Actions:

Analytics Service: Track active users (DAU)
Gamification Service: Update streak (daily activity)

2. Knowledge Domain Events

Event: `knowledge.question.posted`

Version: 1.0.0 Producer: Knowledge Service Consumers: Gamification Service, Search Service, Notification Service Description: Emitted when a user posts a new question. Schema:

{
  "event_type": "knowledge.question.posted",
  "event_version": "1.0.0",
  "timestamp": "2025-12-16T15:30:00Z",
  "payload": {
    "question_id": "qst_abc123",
    "user_id": "usr_abc123",
    "title": "How do I implement event sourcing in Go?",
    "body": "I'm building an event-driven system...",
    "tags": ["go", "event-sourcing", "architecture"],
    "areas": ["area_programming", "area_go"],
    "visibility": "public",
    "files": [
      {
        "file_id": "file_xyz",
        "file_name": "diagram.png",
        "file_size": 1024000,
        "mime_type": "image/png"
      }
    ]
  }
}

Consumer Actions:

Gamification Service: Award +5 XP to user
Search Service: Index question for search
Notification Service: Notify followers of related areas

Event: `knowledge.answer.submitted`

Version: 1.0.0 Producer: Knowledge Service Consumers: Gamification Service, Notification Service Description: Emitted when a user submits an answer to a question. Schema:

{
  "event_type": "knowledge.answer.submitted",
  "event_version": "1.0.0",
  "timestamp": "2025-12-16T16:00:00Z",
  "payload": {
    "answer_id": "ans_def456",
    "question_id": "qst_abc123",
    "user_id": "usr_xyz789",
    "body": "Here's how you can implement event sourcing...",
    "code_snippets": [
      {
        "language": "go",
        "code": "type Event struct {...}"
      }
    ]
  }
}

Consumer Actions:

Gamification Service: Award +10 XP to answerer
Notification Service: Notify question author

Event: `knowledge.answer.accepted`

Version: 1.0.0 Producer: Knowledge Service Consumers: Gamification Service, Notification Service Description: Emitted when question author accepts an answer as the best answer. Schema:

{
  "event_type": "knowledge.answer.accepted",
  "event_version": "1.0.0",
  "timestamp": "2025-12-16T16:30:00Z",
  "payload": {
    "answer_id": "ans_def456",
    "question_id": "qst_abc123",
    "question_author": "usr_abc123",
    "answer_author": "usr_xyz789"
  }
}

Consumer Actions:

Gamification Service: Award +50 XP to answer author
Notification Service: Notify answer author

Event: `knowledge.insight.published`

Version: 1.0.0 Producer: Knowledge Service Consumers: Gamification Service, Search Service, Notification Service Description: Emitted when a user publishes an insight. Schema:

{
  "event_type": "knowledge.insight.published",
  "event_version": "1.0.0",
  "timestamp": "2025-12-16T17:00:00Z",
  "payload": {
    "insight_id": "ins_ghi789",
    "user_id": "usr_abc123",
    "title": "Event-Driven Architecture Best Practices",
    "body": "# Introduction\n\nEvent-driven architecture...",
    "insight_type": "article",
    "tags": ["architecture", "events", "best-practices"],
    "areas": ["area_architecture"],
    "co_authors": [],
    "estimated_read_time_minutes": 10
  }
}

Consumer Actions:

Gamification Service: Award +25 XP
Search Service: Index insight
Notification Service: Notify followers

Event: `knowledge.discussion.started`

Version: 1.0.0 Producer: Knowledge Service Consumers: Gamification Service, Search Service, Notification Service Description: Emitted when a user starts a discussion. Schema:

{
  "event_type": "knowledge.discussion.started",
  "event_version": "1.0.0",
  "timestamp": "2025-12-16T17:30:00Z",
  "payload": {
    "discussion_id": "dsc_jkl012",
    "user_id": "usr_abc123",
    "question": "What's your favorite Go web framework?",
    "description": "I'm evaluating frameworks for a new project...",
    "poll_options": ["Gin", "Echo", "Fiber", "Chi"],
    "tags": ["go", "web-frameworks"],
    "areas": ["area_go"]
  }
}

Consumer Actions:

Gamification Service: Award +10 XP
Search Service: Index discussion
Notification Service: Notify area followers

Event: `knowledge.resource.shared`

Version: 1.0.0 Producer: Knowledge Service Consumers: Gamification Service, Search Service Description: Emitted when a user shares a resource. Schema:

{
  "event_type": "knowledge.resource.shared",
  "event_version": "1.0.0",
  "timestamp": "2025-12-16T18:00:00Z",
  "payload": {
    "resource_id": "res_mno345",
    "user_id": "usr_abc123",
    "resource_type": "course",
    "title": "Complete Guide to Event Sourcing",
    "url": "https://example.com/course",
    "description": "Comprehensive course on event sourcing...",
    "tags": ["event-sourcing", "cqrs"],
    "areas": ["area_architecture"],
    "metadata": {
      "author": "Martin Fowler",
      "duration_hours": 10,
      "price_usd": 49.99
    }
  }
}

Consumer Actions:

Gamification Service: Award +5 XP
Search Service: Index resource

Version: 1.0.0 Producer: Knowledge Service Consumers: Gamification Service, Notification Service Description: Emitted when a user likes content. Schema:

{
  "event_type": "social.content.liked",
  "event_version": "1.0.0",
  "timestamp": "2025-12-16T18:30:00Z",
  "payload": {
    "like_id": "lke_pqr678",
    "content_type": "question",
    "content_id": "qst_abc123",
    "content_author": "usr_abc123",
    "liker_user_id": "usr_xyz789"
  }
}

Consumer Actions:

Gamification Service: Award +2 XP to content author
Notification Service: Notify content author (batched)

Version: 1.0.0 Producer: Knowledge Service Consumers: Gamification Service, Notification Service Description: Emitted when a user adds a comment. Schema:

{
  "event_type": "social.comment.added",
  "event_version": "1.0.0",
  "timestamp": "2025-12-16T19:00:00Z",
  "payload": {
    "comment_id": "cmt_stu901",
    "content_type": "insight",
    "content_id": "ins_ghi789",
    "content_author": "usr_abc123",
    "commenter_user_id": "usr_xyz789",
    "body": "Great article! I've been implementing this...",
    "parent_comment_id": null
  }
}

Consumer Actions:

Gamification Service: Award +3 XP to commenter
Notification Service: Notify content author and parent commenter

Version: 1.0.0 Producer: Knowledge Service Consumers: Gamification Service, Notification Service Description: Emitted when a user upvotes content. Schema:

{
  "event_type": "social.content.upvoted",
  "event_version": "1.0.0",
  "timestamp": "2025-12-16T19:30:00Z",
  "payload": {
    "vote_id": "vte_vwx234",
    "content_type": "answer",
    "content_id": "ans_def456",
    "content_author": "usr_xyz789",
    "voter_user_id": "usr_abc123",
    "vote_value": 1
  }
}

Consumer Actions:

Gamification Service: Award +5 XP to content author
Notification Service: Notify content author (batched)

Version: 1.0.0 Producer: User Service Consumers: Gamification Service, Notification Service Description: Emitted when a user follows another user. Schema:

{
  "event_type": "social.user.followed",
  "event_version": "1.0.0",
  "timestamp": "2025-12-16T20:00:00Z",
  "payload": {
    "follower_user_id": "usr_abc123",
    "followed_user_id": "usr_xyz789"
  }
}

Consumer Actions:

Gamification Service: Check follower milestones (10, 100, 1000 followers)
Notification Service: Notify followed user

4. Gamification Domain Events

Event: `gamification.xp.earned`

Version: 1.0.0 Producer: Gamification Service Consumers: Real-Time Service, Notification Service Description: Emitted when a user earns XP. Schema:

{
  "event_type": "gamification.xp.earned",
  "event_version": "1.0.0",
  "timestamp": "2025-12-16T20:30:00Z",
  "payload": {
    "transaction_id": "xp_txn_abc123",
    "user_id": "usr_abc123",
    "xp_amount": 25,
    "xp_source": "insight_published",
    "related_entity_id": "ins_ghi789",
    "total_xp_after": 1025,
    "daily_xp_earned_today": 75
  }
}

Consumer Actions:

Real-Time Service: Push XP notification to user’s active WebSocket
Notification Service: Add to notification feed

Event: `gamification.level.up`

Version: 1.0.0 Producer: Gamification Service Consumers: Real-Time Service, Notification Service, User Service Description: Emitted when a user levels up. Schema:

{
  "event_type": "gamification.level.up",
  "event_version": "1.0.0",
  "timestamp": "2025-12-16T21:00:00Z",
  "payload": {
    "user_id": "usr_abc123",
    "old_level": 4,
    "new_level": 5,
    "level_title": "Growing Tree",
    "xp_required_for_next": 1000,
    "unlocked_features": ["downvote", "create_collections"]
  }
}

Consumer Actions:

Real-Time Service: Show level-up animation
Notification Service: Send congratulatory notification
User Service: Update user level badge

Event: `gamification.achievement.unlocked`

Version: 1.0.0 Producer: Gamification Service Consumers: Real-Time Service, Notification Service Description: Emitted when a user unlocks an achievement. Schema:

{
  "event_type": "gamification.achievement.unlocked",
  "event_version": "1.0.0",
  "timestamp": "2025-12-16T21:30:00Z",
  "payload": {
    "achievement_id": "ach_week_warrior",
    "user_id": "usr_abc123",
    "achievement_name": "Week Warrior",
    "achievement_description": "Maintain a 7-day activity streak",
    "achievement_tier": "gold",
    "xp_bonus": 100,
    "badge_image_url": "https://cdn.tektree.com/badges/week_warrior.svg"
  }
}

Consumer Actions:

Real-Time Service: Show achievement unlock animation
Notification Service: Send achievement notification

Event: `gamification.streak.extended`

Version: 1.0.0 Producer: Gamification Service Consumers: Real-Time Service Description: Emitted when a user extends their daily streak. Schema:

{
  "event_type": "gamification.streak.extended",
  "event_version": "1.0.0",
  "timestamp": "2025-12-16T22:00:00Z",
  "payload": {
    "user_id": "usr_abc123",
    "streak_count": 7,
    "streak_milestone": true,
    "xp_bonus": 100
  }
}

Consumer Actions:

Real-Time Service: Update streak counter UI

Event: `gamification.leaderboard.updated`

Version: 1.0.0 Producer: Gamification Service Consumers: Real-Time Service Description: Emitted when leaderboard rankings change (throttled to avoid spam). Schema:

{
  "event_type": "gamification.leaderboard.updated",
  "event_version": "1.0.0",
  "timestamp": "2025-12-16T22:30:00Z",
  "payload": {
    "leaderboard_type": "weekly_xp",
    "top_users": [
      {
        "user_id": "usr_abc123",
        "rank": 1,
        "xp": 5000
      },
      {
        "user_id": "usr_xyz789",
        "rank": 2,
        "xp": 4800
      }
    ]
  }
}

Consumer Actions:

Real-Time Service: Push leaderboard updates to subscribed clients

5. Payment Domain Events

Event: `payment.subscription.created`

Version: 1.0.0 Producer: Payment Service Consumers: User Service, Analytics Service Description: Emitted when a subscription is created (including free tier). Schema:

{
  "event_type": "payment.subscription.created",
  "event_version": "1.0.0",
  "timestamp": "2025-12-16T23:00:00Z",
  "payload": {
    "subscription_id": "sub_yzabcd",
    "user_id": "usr_abc123",
    "tier": "free",
    "billing_cycle": "monthly",
    "start_date": "2025-12-16T23:00:00Z",
    "trial_ends_at": null,
    "quotas": {
      "areas": 10,
      "questions_per_month": 20,
      "insights_per_month": 5,
      "storage_mb": 100
    }
  }
}

Consumer Actions:

User Service: Update user tier badge
Analytics Service: Track subscription creation

Event: `payment.subscription.upgraded`

Version: 1.0.0 Producer: Payment Service Consumers: User Service, Gamification Service, Notification Service Description: Emitted when a user upgrades their subscription tier. Schema:

{
  "event_type": "payment.subscription.upgraded",
  "event_version": "1.0.0",
  "timestamp": "2025-12-16T23:30:00Z",
  "payload": {
    "subscription_id": "sub_yzabcd",
    "user_id": "usr_abc123",
    "old_tier": "free",
    "new_tier": "pro",
    "effective_date": "2025-12-16T23:30:00Z",
    "prorated_charge": 9.00,
    "new_quotas": {
      "areas": "unlimited",
      "questions_per_month": 200,
      "insights_per_month": 50,
      "storage_mb": 10240
    }
  }
}

Consumer Actions:

User Service: Update user tier badge
Gamification Service: Award +200 XP bonus
Notification Service: Send upgrade confirmation

Event: `payment.quota.exceeded`

Version: 1.0.0 Producer: Payment Service (quota check) Consumers: Notification Service Description: Emitted when a user exceeds their quota limit. Schema:

{
  "event_type": "payment.quota.exceeded",
  "event_version": "1.0.0",
  "timestamp": "2025-12-17T00:00:00Z",
  "payload": {
    "user_id": "usr_abc123",
    "tier": "free",
    "quota_type": "questions_per_month",
    "quota_limit": 20,
    "current_usage": 21,
    "action_blocked": true
  }
}

Consumer Actions:

Notification Service: Send upgrade prompt notification

Event: `payment.webhook.received`

Version: 1.0.0 Producer: Payment Service Consumers: Analytics Service (for auditing) Description: Emitted when a Polar webhook is received (for audit trail). Schema:

{
  "event_type": "payment.webhook.received",
  "event_version": "1.0.0",
  "timestamp": "2025-12-17T00:30:00Z",
  "payload": {
    "webhook_id": "whk_efghij",
    "polar_event_type": "checkout.completed",
    "polar_event_id": "evt_polar_123",
    "signature_valid": true,
    "processed": true
  }
}

Consumer Actions:

Analytics Service: Log webhook for debugging

6. Real-Time Domain Events

Event: `realtime.user.joined`

Version: 1.0.0 Producer: Real-Time Service Consumers: Analytics Service Description: Emitted when a user joins a real-time channel (presence). Schema:

{
  "event_type": "realtime.user.joined",
  "event_version": "1.0.0",
  "timestamp": "2025-12-17T01:00:00Z",
  "payload": {
    "user_id": "usr_abc123",
    "channel": "content:qst_abc123",
    "connection_id": "conn_klmnop"
  }
}

Consumer Actions:

Analytics Service: Track real-time engagement

Event: `notification.sent`

Version: 1.0.0 Producer: Notification Service Consumers: Analytics Service Description: Emitted when a notification is successfully sent. Schema:

{
  "event_type": "notification.sent",
  "event_version": "1.0.0",
  "timestamp": "2025-12-17T01:30:00Z",
  "payload": {
    "notification_id": "ntf_qrstuv",
    "user_id": "usr_abc123",
    "notification_type": "achievement_unlocked",
    "delivery_method": "websocket",
    "delivered": true
  }
}

Consumer Actions:

Analytics Service: Track notification engagement

Event Choreography Patterns

Pattern 1: User Registration Flow

Pattern 2: Content Engagement Flow

Pattern 3: Achievement Unlock Flow

Event Versioning Strategy

Semantic Versioning

Events follow semantic versioning (MAJOR.MINOR.PATCH):

MAJOR: Breaking changes (field removed, type changed)
MINOR: Backward-compatible additions (new field)
PATCH: Documentation or clarification changes

Versioning Rules

Always include event_version field in event payload
Consumers must handle multiple versions gracefully
Deprecated versions supported for 6 months before removal
Breaking changes require migration plan

Example: Adding a New Field (Minor Version)

v1.0.0:

{
  "event_type": "user.registered",
  "event_version": "1.0.0",
  "payload": {
    "user_id": "usr_abc123",
    "email": "user@example.com"
  }
}

v1.1.0 (Add new field):

{
  "event_type": "user.registered",
  "event_version": "1.1.0",
  "payload": {
    "user_id": "usr_abc123",
    "email": "user@example.com",
    "referral_code": "REF123"  // New field
  }
}

Consumer Handling:

type UserRegisteredV1 struct {
    UserID string `json:"user_id"`
    Email  string `json:"email"`
    ReferralCode string `json:"referral_code,omitempty"` // Optional
}

func handleUserRegistered(event Event) {
    var payload UserRegisteredV1
    json.Unmarshal(event.Payload, &payload)

    // Handle with or without referral_code
    if payload.ReferralCode != "" {
        // Process referral
    }
}

Event Retention Policies

Event Category	Retention Period	Storage	Rationale
User events	Indefinite	Event Store	Audit trail
Knowledge events	Indefinite	Event Store	Content history
Gamification events	2 years	Event Store	Historical analytics
Payment events	7 years	Event Store	Legal compliance
Social events	1 year	Event Store	Recent activity
Real-time events	7 days	Redis Streams	Operational only
Notification events	30 days	MongoDB	Recent history

Archival Strategy:

Events older than retention period moved to cold storage (S3)
Archived events compressed (gzip)
Archived events indexed for compliance queries
Automatic archival job runs weekly

Event Publishing Guarantees

At-Least-Once Delivery

TekTree uses at-least-once delivery semantics:

Events may be delivered multiple times
Consumers must be idempotent
Use event_id for deduplication

Idempotency Pattern

type EventProcessor struct {
    processedEvents *sync.Map
}

func (p *EventProcessor) ProcessEvent(event Event) error {
    // Check if already processed
    if _, exists := p.processedEvents.Load(event.EventID); exists {
        log.Info("Event already processed, skipping", "event_id", event.EventID)
        return nil
    }

    // Process event
    if err := p.doProcess(event); err != nil {
        return err
    }

    // Mark as processed
    p.processedEvents.Store(event.EventID, time.Now())
    return nil
}

Event Ordering Guarantees

Per-Aggregate Ordering

Events for the same aggregate are processed in order:

Use correlation_id to group related events
Redis Streams guarantees order within a stream
Consumers use consumer groups for parallel processing

Global Ordering

Global ordering is not guaranteed:

Events from different services may arrive out of order
Use timestamps for eventual consistency
Design for commutative operations where possible

Dead Letter Queue (DLQ)

DLQ Policy

Events that fail processing after 3 retries are moved to DLQ:

First retry: Immediate
Second retry: 10 seconds delay
Third retry: 60 seconds delay
If still failing: Move to DLQ

DLQ Monitoring

Alert when DLQ size > 100
Daily DLQ report sent to operations team
Manual review and reprocessing

Event Bus Performance Targets

Metric	Target
Event publishing latency (p95)	< 10ms
Event delivery latency (p95)	< 100ms
Throughput (sustained)	1,000 events/sec
Throughput (burst)	5,000 events/sec
Event backlog size (max)	10,000 events

Event Catalog Maintenance

Ownership

Domain Event Owner: Team responsible for the domain (User, Knowledge, etc.)
Event Catalog Maintainer: Platform team
Review Frequency: Quarterly

Change Process

Propose event schema change (GitHub PR to this document)
Review with domain team
Update event version if breaking change
Update consumers to handle new version
Deploy consumers before deploying producers
Monitor for errors

Document Status: ✅ Complete Related Documents: ARCHITECTURE_OVERVIEW.md, DATA_MODELS.md, API_CONTRACTS.md

Overview

Architecture

Features

API

Tasksets

​TekTree Event Catalog

​Document Purpose

​Event Taxonomy

​Event Schema Standards

​1. User Domain Events

​Event: user.registered

​Event: user.profile.updated

​Event: user.authenticated

​2. Knowledge Domain Events

​Event: knowledge.question.posted

​Event: knowledge.answer.submitted

​Event: knowledge.answer.accepted

​Event: knowledge.insight.published

​Event: knowledge.discussion.started

​Event: knowledge.resource.shared

​3. Social Domain Events

​Event: social.content.liked

​Event: social.comment.added

​Event: social.content.upvoted

​Event: social.user.followed

​4. Gamification Domain Events

​Event: gamification.xp.earned

​Event: gamification.level.up

​Event: gamification.achievement.unlocked

​Event: gamification.streak.extended

​Event: gamification.leaderboard.updated

​5. Payment Domain Events

​Event: payment.subscription.created

​Event: payment.subscription.upgraded

​Event: payment.quota.exceeded

​Event: payment.webhook.received

​6. Real-Time Domain Events

​Event: realtime.user.joined

​Event: notification.sent

​Event Choreography Patterns

​Pattern 1: User Registration Flow

​Pattern 2: Content Engagement Flow

​Pattern 3: Achievement Unlock Flow

​Event Versioning Strategy

​Semantic Versioning

​Versioning Rules

​Example: Adding a New Field (Minor Version)

​Event Retention Policies

​Event Publishing Guarantees

​At-Least-Once Delivery

​Idempotency Pattern

​Event Ordering Guarantees

​Per-Aggregate Ordering

​Global Ordering

​Dead Letter Queue (DLQ)

​DLQ Policy

​DLQ Monitoring

​Event Bus Performance Targets

​Event Catalog Maintenance

​Ownership

​Change Process

TekTree Event Catalog

Document Purpose

Event Taxonomy

Event Schema Standards

1. User Domain Events

Event: `user.registered`

Event: `user.profile.updated`

Event: `user.authenticated`

2. Knowledge Domain Events

Event: `knowledge.question.posted`

Event: `knowledge.answer.submitted`

Event: `knowledge.answer.accepted`

Event: `knowledge.insight.published`

Event: `knowledge.discussion.started`

Event: `knowledge.resource.shared`

3. Social Domain Events

Event: `social.content.liked`

Event: `social.comment.added`

Event: `social.content.upvoted`

Event: `social.user.followed`

4. Gamification Domain Events

Event: `gamification.xp.earned`

Event: `gamification.level.up`

Event: `gamification.achievement.unlocked`

Event: `gamification.streak.extended`

Event: `gamification.leaderboard.updated`

5. Payment Domain Events

Event: `payment.subscription.created`

Event: `payment.subscription.upgraded`

Event: `payment.quota.exceeded`

Event: `payment.webhook.received`

6. Real-Time Domain Events

Event: `realtime.user.joined`

Event: `notification.sent`

Event Choreography Patterns

Pattern 1: User Registration Flow

Pattern 2: Content Engagement Flow

Pattern 3: Achievement Unlock Flow

Event Versioning Strategy

Semantic Versioning

Versioning Rules

Example: Adding a New Field (Minor Version)

Event Retention Policies

Event Publishing Guarantees

At-Least-Once Delivery

Idempotency Pattern

Event Ordering Guarantees

Per-Aggregate Ordering

Global Ordering

Dead Letter Queue (DLQ)

DLQ Policy

DLQ Monitoring

Event Bus Performance Targets

Event Catalog Maintenance

Ownership

Change Process