Composite Service

Orchestrator service that coordinates atomic microservices, handles Pub/Sub subscriptions, and provides unified API endpoints.

📋 Overview

The Composite Service acts as the central orchestrator for the microservices architecture:

Routes requests to appropriate atomic services (Users, Events, Feed)
Handles Pub/Sub message consumption for email notifications
Provides composite endpoints (e.g., user feed with events and posts)
Manages GraphQL API
Coordinates cross-service operations

🏗️ Architecture

API Gateway → Composite Service → Atomic Services
                ↓
            Pub/Sub Subscriptions
                ↓
            Email Notifications

Port: 8004
Authentication: Trusts x-firebase-uid header from API Gateway
Pub/Sub: Subscribes to event-created and user-created topics

🚀 Setup

Prerequisites

Python 3.9+
Firebase service account key
Google Cloud Pub/Sub (for email notifications)
SMTP server credentials (for email sending)

Installation

Install dependencies
```
pip install -r requirements.txt
```

Configure environment variables Create a .env file:

# Service URLs
USERS_SERVICE_URL=http://localhost:8001
EVENTS_SERVICE_URL=http://localhost:8002
FEED_SERVICE_URL=http://localhost:8003

# GCP Configuration
GCP_PROJECT_ID=your-project-id
GOOGLE_CLOUD_PROJECT=your-project-id

# Pub/Sub Topics
PUBSUB_EVENT_CREATED_TOPIC=event-created
PUBSUB_USER_CREATED_TOPIC=user-created

# Pub/Sub Subscriptions
PUBSUB_EVENT_NOTIFICATION_SUB=event-notification-sub
PUBSUB_USER_WELCOME_SUB=user-welcome-sub

# SMTP Configuration
SMTP_HOST=smtp.gmail.com
SMTP_PORT=587
SMTP_USER=your-email@gmail.com
SMTP_PASS=your-app-password
SMTP_FROM=your-email@gmail.com

# Firebase
FIREBASE_SERVICE_ACCOUNT_PATH=./serviceAccountKey.json

Add Firebase service account key
- Download from Firebase Console
- Place as serviceAccountKey.json in service directory
Set up Pub/Sub topics and subscriptions See README_PUBSUB.md for detailed instructions.
Run the service
```
uvicorn main:app --host 0.0.0.0 --port 8004
```
The service will automatically start Pub/Sub subscribers in background threads.

🔧 Environment Variables

Variable	Description	Default	Required
`USERS_SERVICE_URL`	Users Service URL	`http://localhost:8001`	Yes
`EVENTS_SERVICE_URL`	Event Service URL	`http://localhost:8002`	Yes
`FEED_SERVICE_URL`	Feed Service URL	`http://localhost:8003`	Yes
`GCP_PROJECT_ID`	GCP project ID	-	Yes
`GOOGLE_CLOUD_PROJECT`	Same as GCP_PROJECT_ID	-	Yes
`PUBSUB_EVENT_CREATED_TOPIC`	Pub/Sub topic name	`event-created`	No
`PUBSUB_USER_CREATED_TOPIC`	Pub/Sub topic name	`user-created`	No
`PUBSUB_EVENT_NOTIFICATION_SUB`	Pub/Sub subscription name	`event-notification-sub`	No
`PUBSUB_USER_WELCOME_SUB`	Pub/Sub subscription name	`user-welcome-sub`	No
`SMTP_HOST`	SMTP server host	-	Yes (for emails)
`SMTP_PORT`	SMTP server port	`587`	No
`SMTP_USER`	SMTP username	-	Yes (for emails)
`SMTP_PASS`	SMTP password	-	Yes (for emails)
`SMTP_FROM`	From email address	-	Yes (for emails)
`FIREBASE_SERVICE_ACCOUNT_PATH`	Path to Firebase service account JSON	`./serviceAccountKey.json`	No

📡 API Endpoints

Composite Endpoints

`GET /api/users/me/feed`

Get personalized feed for current user (events + posts)

Query Parameters:

skip_posts: Number of posts to skip (default: 0)
limit_posts: Number of posts to return (default: 5, max: 100)
skip_events: Number of events to skip (default: 0)
limit_events: Number of events to return (default: 5, max: 100)

Response:

{
  "user_id": 1,
  "events": [
    {
      "event_id": 1,
      "title": "Tech Meetup",
      "start_time": "2024-01-15T18:00:00",
      ...
    }
  ],
  "posts": [
    {
      "post_id": 1,
      "title": "My Post",
      "created_at": "2024-01-01T00:00:00",
      ...
    }
  ]
}

Proxy Endpoints

The Composite Service proxies requests to atomic services:

/api/users/* → Users Service
/api/events/* → Event Service
/api/posts/* → Feed Service
/api/friends/* → Users Service (friend management)

All requests are forwarded with the x-firebase-uid header.

GraphQL Endpoint

`POST /graphql`

GraphQL API endpoint

Query Example:

query {
  users {
    user_id
    username
    email
  }
  events {
    event_id
    title
    location
  }
}

See graphql_api/schema.py for available queries and mutations.

📨 Pub/Sub Integration

Subscriptions

The service subscribes to two Pub/Sub topics:

event-notification-sub (subscribes to event-created topic)
- Triggered when a new event is created
- Sends email notification to event creator
user-welcome-sub (subscribes to user-created topic)
- Triggered when a new user is created
- Sends welcome email to new user

Message Flow

Event Service → Publishes to "event-created" topic
                ↓
Composite Service → Consumes message
                ↓
Email Service → Sends notification email

Starting Subscribers

Subscribers start automatically when the service starts:

# In main.py
start_event_subscriber()
start_user_subscriber()

📧 Email Service

The service includes email functionality for:

Event creation notifications
User welcome emails

SMTP Configuration:

Supports Gmail, Outlook, and other SMTP servers
Uses TLS/STARTTLS for secure connections
Requires app-specific password for Gmail

🔐 Authentication

This service does not perform Firebase authentication directly. It:

Receives x-firebase-uid header from API Gateway
Forwards this header to atomic services
Uses firebase_uid from request.state (set by API Gateway middleware)

🐳 Docker Deployment

Build Image

docker build -t composite-service .

Run Container

docker run -p 8004:8004 \
  -e USERS_SERVICE_URL=http://users-service:8001 \
  -e EVENTS_SERVICE_URL=http://event-service:8002 \
  -e FEED_SERVICE_URL=http://feed-service:8003 \
  -e GCP_PROJECT_ID=your-project-id \
  -e SMTP_HOST=smtp.gmail.com \
  -e SMTP_USER=your-email@gmail.com \
  -e SMTP_PASS=your-app-password \
  composite-service

☁️ GCP Cloud Run Deployment

The service is deployed to Cloud Run with:

VPC Connector for accessing VM services
Pub/Sub subscriber permissions
Environment variables configured via deployment script
Background threads for Pub/Sub subscribers

See ../GCP_DEPLOYMENT_GUIDE.md for details.

🧪 Testing

Health Check

curl http://localhost:8004/

Get User Feed

curl -H "x-firebase-uid: your-firebase-uid" \
     "http://localhost:8004/api/users/me/feed?limit_posts=10&limit_events=10"

Test Pub/Sub (Local)

python debug_pubsub.py

Test Email Service

from email_service import send_email

send_email(
    to="test@example.com",
    subject="Test Email",
    body="This is a test email"
)

📚 API Documentation

Interactive API documentation available at:

Swagger UI: http://localhost:8004/docs
ReDoc: http://localhost:8004/redoc
OpenAPI JSON: http://localhost:8004/openapi.json
GraphQL Playground: http://localhost:8004/graphql (if enabled)

🔍 Error Handling

The service returns standard HTTP status codes:

200 OK: Successful request
400 Bad Request: Invalid request data
401 Unauthorized: Missing or invalid x-firebase-uid header
404 Not Found: Resource not found
502 Bad Gateway: Downstream service unavailable
500 Internal Server Error: Server error

🎯 Features

Service Orchestration: Routes requests to appropriate atomic services
Pub/Sub Integration: Event-driven email notifications
Composite Endpoints: Unified endpoints combining multiple services
GraphQL API: Flexible querying of data
Error Handling: Graceful handling of downstream service failures
Request Forwarding: Maintains authentication headers across services

📝 Notes

Pub/Sub subscribers run in background threads and persist for the service lifetime
Email service uses synchronous SMTP connections
Service URLs can point to Cloud Run URLs or VM private IPs
The service acts as a reverse proxy for atomic services

📖 Additional Documentation

Pub/Sub Setup Guide - Detailed Pub/Sub configuration
GraphQL Schema - GraphQL API schema

🤝 Contributing

When adding new endpoints:

Add route to routers/composite_router.py
Use request.state.firebase_uid for user identification
Forward requests to atomic services using forward_request() helper
Add proper error handling
Update this README with endpoint documentation

Name		Name	Last commit message	Last commit date
Latest commit History 14 Commits
__pycache__		__pycache__
graphql_api		graphql_api
pubsub		pubsub
routers		routers
.gitignore		.gitignore
README.md		README.md
README_PUBSUB.md		README_PUBSUB.md
auth.py		auth.py
check_subscribers.py		check_subscribers.py
cross_account_auth.py		cross_account_auth.py
debug_pubsub.py		debug_pubsub.py
email_service.py		email_service.py
helpers.py		helpers.py
main.py		main.py
requirements.txt		requirements.txt

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