This content originally appeared on DEV Community and was authored by Jaydeep Kumar Sahu
Push Notification Engine
Designing a Push Notification System
Business Services
These services are responsible for triggering notifications.
1.1 Service
• Triggers single notifications for events like order confirmation, shipping, and delivery updates.
• Publishes notification events (e.g., OrderConfirmed, OrderShipped) to a message broker (e.g., Azure Service Bus, Kafka).
• Generates batch notifications, such as payment reminders or transaction summaries.
• Publishes batch events to the message broker with payloads containing multiple user and notification details.Notification Gateway
The Notification Gateway acts as the entry point for all notification events from business services. Responsibilities:
• Ingestion: Consumes events from the message broker (via topics/queues).
• Decoupling: Abstracts business services from the downstream notification system.
• Transformation: Converts raw event data into a standard notification format with attributes like:
o User ID
o Notification type
o Payload (e.g., message, metadata)Notification Distribution
Responsible for preparing and prioritizing notifications before delivery.
3.1 Validation
• Validates the incoming notification data:
o Check if the user exists.
o Validate channel preferences (e.g., if the user has opted out of certain channels).
o Ensure all required fields (e.g., template ID, message content) are populated.
3.2 Scheduler
• Handles notifications that are scheduled for future delivery (e.g., reminders or promotional offers).
• Stores scheduled notifications in a scheduler store (SQL/NoSQL DB).
• Periodically processes the scheduler store to send notifications at the right time.
3.3 Priority
• Assigns priority to notifications based on type:
o High priority: Payment failure, OTPs.
o Medium priority: Order updates, shipping details.
o Low priority: Marketing or promotional notifications.
• Routes high-priority notifications for immediate delivery while queuing others.
3.4 Template Management
• Dynamically generates notification content based on predefined templates.
3.4.1 Template Repository
• Stores reusable templates for notifications (e.g., OrderConfirmation, PaymentReminder) in a template repository (SQL/NoSQL).
• Templates include placeholders for dynamic content, e.g.: Hello {UserName}, your order #{OrderID} has been confirmed!Notification Router (Queues)
• Routes validated and prepared notifications to appropriate channels.
• Uses message queues (e.g., RabbitMQ, Azure Service Bus) for decoupling and reliability.
o Example: Separate queues for Email, SMS, In-App Notifications, and Social Media.
• Prioritizes and batches notifications for processing by specific channel workers.Channels
Responsible for delivering notifications through different mediums. Each channel has a dedicated service.
5.1 Email
• Sends email notifications using services like SendGrid, AWS SES, or SMTP.
• Supports fallback mechanisms for failed deliveries (e.g., retry queue).
5.2 SMS
• Sends SMS notifications via providers like Twilio, Nexmo, or Azure Communication Services.
• Handles rate limiting and retries for failed SMS deliveries.
5.3 In-App Delivery
• Delivers notifications to the in-app notification center.
• Real-time delivery via SignalR or WebSockets for active users.
• For offline users, stores notifications in a database and syncs when the app is opened.
5.4 Social Media
• Integrates with platforms like WhatsApp Business API, Twitter, or Facebook Messenger for social notifications.
• Manages authorization tokens and API limits for these platforms.Notification Tracing and Analytics
Provides observability and insights into the notification system.
6.1 Tracing
• Logs each step in the notification lifecycle:
o Event ingestion
o Validation and processing
o Routing and delivery
• Includes unique notification IDs for tracking individual notifications across services.
6.2 Analytics
• Tracks key metrics like:
o Delivery rates
o Open rates (for email and in-app notifications)
o Click-through rates (CTR) for actionable notifications
• Stores data in an analytics store (e.g., Azure Data Explorer, Elasticsearch) for real-time and historical analysis.User Channel Preferences
Allows users to customize their notification preferences.
7.1 Preference Management
• Users can set preferences via a UI (e.g., mobile app or website):
o Opt in/out of specific channels (e.g., disable SMS, enable email).
o Choose preferences for notification types (e.g., promotional, transactional).
7.2 Storage
• Stores preferences in a database (e.g., SQL, Cosmos DB) with mappings like:
o UserID → Channel Preferences (e.g., Email=true, SMS=false).
7.3 Enforcement
• During validation, checks preferences to ensure notifications are sent only to allowed channels.
Tech Stack Recommendations
Backend
• ASP.NET Core: For implementing the Notification Gateway, Validation, and Scheduler.
• Message Broker: Azure Service Bus / RabbitMQ / Kafka for decoupling and queuing.
• Database:
o SQL: For structured data like user preferences and templates.
o NoSQL (Cosmos DB / MongoDB): For storing logs and high-volume event data.
Frontend
• React/Angular/Vue.js: For building user interfaces for managing preferences and analytics dashboards.
Notification Channels
• Email: SendGrid, AWS SES.
• SMS: Twilio, Nexmo, Azure Communication Services.
• In-App: SignalR for real-time delivery.
Monitoring and Analytics
• Azure Monitor: For system health monitoring.
• Application Insights: For telemetry and tracing.
• Power BI / Grafana: For visualizing analytics.
Workflow Example
- Order Service publishes an OrderConfirmed event to the broker.
- Notification Gateway ingests the event and validates it.
- The event is enriched with user preferences and routed to the Notification Router.
- The router forwards it to the Email Queue.
- The Email Channel Worker picks it up, formats the message using the Template Repository, and sends it via SendGrid.
- Delivery logs are stored in the Tracing System, and metrics are updated in the Analytics Store.
High Level Roadmap
Pre-Implementation Checklist
Before diving into implementation, ensure you have the following ready:
a. Business Requirements
• Finalize the notification types (e.g., order updates, payment reminders).
• Define user channel preferences and their impact on notification delivery.
• Confirm the SLAs (e.g., real-time vs batch notifications).
b. High-Level Architecture
• Validate the architecture with stakeholders to ensure alignment.
• Decide on the tech stack:
o Backend: ASP.NET Core.
o Message broker: Azure Service Bus / RabbitMQ / Kafka.
o Channels: SendGrid, Twilio, SignalR, etc.
o Database: SQL for user/channel preferences and templates; NoSQL for logs and analytics.
c. Tools and Services
• Set up Azure resources (if using Azure): Service Bus, App Services, SQL Database, etc.
• Choose notification channel providers and integrate their SDKs/APIs.
d. Team Readiness
• Assign team roles:
o Backend developers for core engine and APIs.
o Frontend developers for user preference management UI.
o DevOps for CI/CD pipelines.Step-by-Step Implementation
Step 1: Build the FoundationSet Up Development Environment:
o Create a new solution in ASP.NET Core.
o Set up databases for preferences, templates, and logs.Develop the Core Notification Schema:
o Define a standardized notification payload format.
Step 2: Implement User Preferences Management
- Backend API: o Build APIs to CRUD user notification preferences. o Store preferences in a SQL database.
- Frontend Interface: o Create a simple UI for users to update preferences.
Step 3: Create the Notification Gateway
- Message Broker Integration: o Configure the broker (e.g., Azure Service Bus). o Publish events from business services to relevant topics/queues.
- Event Validation: o Create a service to validate incoming events against user preferences.
- Transformation: o Map raw event data to a standardized notification format.
Step 4: Build Notification Router
- Queue Creation: o Set up separate queues for each channel (Email, SMS, In-App, Social Media).
- Routing Logic: o Implement routing rules based on: User preferences. Notification type. Channel availability.
Step 5: Implement Channels
- Email Channel: o Integrate with SendGrid or similar service. o Implement retry logic for failed deliveries.
- SMS Channel: o Integrate with Twilio or Nexmo. o Handle rate limits and retries.
- In-App Channel: o Use SignalR or WebSockets for real-time delivery. o Store unread notifications in the database for offline users.
- Social Media Channel (Optional): o Integrate APIs for WhatsApp, Facebook, or Twitter.
Step 6: Add Scheduler and Batch Processing
- Scheduler: o Implement a job to process notifications scheduled for future delivery.
- Batch Processing: o Create a batch processing service for notifications (e.g., daily payment reminders).
Step 7: Implement Template Management
- Template Repository: o Build APIs to CRUD templates. o Use placeholders for dynamic content (e.g., {UserName}).
- Template Engine: o Integrate a lightweight template engine (e.g., Razor Templates or Handlebars).
Step 8: Add Notification Tracing and Analytics
- Logging: o Log each notification's status (e.g., Sent, Failed, Delivered). o Store logs in a NoSQL database for scalability.
Analytics:
o Implement metrics for delivery success rates, engagement rates, etc.
o Use tools like Power BI, Grafana, or Azure Monitor for dashboards.Roadmap
Phase Task Timeline
Phase 1 Set up database, create core notification schema, and implement user preference management. 1–2 weeks
Phase 2 Develop Notification Gateway and integrate with message broker. 2 weeks
Phase 3 Build Notification Router and implement email/SMS channels. 2–3 weeks
Phase 4 Add in-app delivery and batch processing (scheduler). 1–2 weeks
Phase 5 Implement template management, tracing, and analytics. 2 weeksFinal Review Before Implementation
• Ensure all dependencies (e.g., SDKs for channels, message broker configuration) are ready.
• Conduct a design walkthrough with your team to identify gaps.
• Set up CI/CD pipelines to deploy components iteratively.
Tech Stack
Backend Layer (API and Service Layer)
a. Programming Language
• C# / .NET Core: This is the primary language you'll use to build your backend APIs and core business logic. It's ideal for handling HTTP requests, processing user preferences, and interacting with message queues and databases.
b. Framework
• ASP.NET Core: This is a high-performance framework for building scalable web APIs. You'll use it to create endpoints for handling push notification requests, managing user preferences, and delivering notifications to various channels. It also supports middleware for logging, security, and error handling.
• MassTransit / NServiceBus: These are messaging frameworks that simplify building distributed systems with message queues. They provide features like retries, message scheduling, and fault tolerance, which are crucial for a reliable notification engine.
c. Message Broker
• Azure Service Bus: A fully managed enterprise messaging service from Azure. It can handle large-scale messaging, including queues and topics for message routing. This is especially useful for handling notifications in batches and ensuring message reliability.
• RabbitMQ: An open-source message broker. It supports both queue-based and publish-subscribe messaging models, which would allow you to route and process notifications efficiently.
• Apache Kafka: A distributed event streaming platform. If you need to handle very high throughput, real-time data streaming (such as sending millions of notifications), Kafka would be suitable. It allows for high-scale message delivery and stream processing.
d. Database Layer
• SQL Server: A relational database that you can use for storing structured data like user preferences, notification metadata, templates, and logs.
• Azure SQL Database: A cloud-based version of SQL Server, with built-in scalability and high availability, making it easier to manage in a cloud-based notification engine.
• Cosmos DB: A NoSQL database that offers low-latency, globally distributed data. It is well-suited for scalable, high-performance applications like notifications.
• NoSQL Database (MongoDB, DynamoDB): These databases are better for storing unstructured data, such as logs, user activity, or large datasets that don't require relational schema.
• ElasticSearch: A search engine for handling large datasets and log queries. It's useful if you want to track and analyze delivery metrics and logs.
e. Caching Layer
• Redis: A fast, in-memory key-value store. You can use it to cache user preferences, templates, and frequently queried data to reduce database load and speed up notification delivery.Notification Distribution Layer
a. Notification Scheduler
• Quartz.NET: A powerful library for scheduling jobs. You can use it for delayed or recurring notifications, like sending reminders or batch notifications at specific times.
• Azure Logic Apps / Azure Functions: Serverless solutions that can automatically trigger processes based on time or events. For example, a logic app can trigger the sending of marketing emails every morning at a specific time.
b. Notification Routing & Processing
• Azure Functions / AWS Lambda: These are serverless compute services that can process individual notification requests. For example, a function could receive a message from the queue, format it, and send it to the appropriate channel (email, SMS, etc.).
• Background Services: In ASP.NET Core, you can implement background services using hosted services. These services can run continuously in the background, managing tasks like checking queues and sending notifications.Channels (Email, SMS, In-App, etc.)
a. Email Delivery
• SendGrid / Postmark / Amazon SES: These are third-party email delivery services. They provide easy-to-use APIs to send emails, manage templates, and track delivery performance.
• SMTP: If you prefer to manage email sending internally, you can configure an SMTP server, but this requires more effort for scaling, reliability, and tracking.
b. SMS Delivery
• Twilio / Nexmo / Plivo: These are popular APIs for sending SMS messages. They offer features like phone number verification, message tracking, and delivery reports.
• Sinch: Another option for sending SMS, Voice, and messaging services, often used in telecom industries.
c. Push Notifications (Mobile/Web)
• Firebase Cloud Messaging (FCM): A free and reliable push notification service from Google that allows you to send notifications to iOS, Android, and web applications.
• Azure Notification Hubs: A service in Azure that supports sending push notifications to all types of devices (iOS, Android, Windows Phone, etc.) from a centralized platform.
• OneSignal: A push notification service that supports web, mobile, and email notifications. It’s user-friendly and offers rich analytics.
d. In-App Notifications
• SignalR: A real-time web communication framework in ASP.NET Core. It enables bi-directional communication between the server and client, making it perfect for in-app notifications and real-time updates.
e. Social Media Notifications
• Facebook Graph API / Twitter API: These APIs allow you to post content on social media platforms. You would need to integrate them if you plan to deliver notifications through social media channels.User Preferences and Template Management
a. Template Engine
• Razor: Razor is an excellent templating engine that works out of the box with ASP.NET Core. It is ideal for generating dynamic email content or SMS templates, and you can easily store and render HTML-based templates.
• Handlebars.NET: A flexible template engine that allows you to build dynamic notifications with placeholders (like {UserName} or {OrderId}). It’s easy to integrate with various content types.
• Liquid: A templating engine commonly used in e-commerce platforms, ideal for generating dynamic messages and content for emails or SMS.
b. User Preferences API
• ASP.NET Core Identity: This is a library for user authentication and authorization. It’s perfect for managing user profiles and preferences, such as their notification channel and content preferences.
• JWT (JSON Web Tokens): A standard for securely transmitting information between client and server. You can use JWTs to authenticate API calls related to user preferences.Monitoring, Logging, and Analytics
a. Logging
• Serilog / NLog: Both are logging frameworks for .NET that allow you to track detailed information about notification delivery, failures, retries, and other system events.
• Azure Application Insights: A fully managed monitoring and diagnostic service. It provides powerful tools to detect issues, track requests, and monitor the performance of your notification engine.
b. Analytics
• Power BI: A Microsoft product for visualizing and analyzing data. You can integrate Power BI to track notification delivery success rates, user engagement, and other key metrics.
• Grafana with Prometheus: Grafana provides real-time monitoring dashboards, and Prometheus can collect and store metrics from your notification system.
c. Tracing and Debugging
• ElasticSearch: Use ElasticSearch for querying large volumes of logs, enabling faster debugging and analysis.
• OpenTelemetry: A framework for collecting distributed tracing data across your microservices to ensure that notifications are properly tracked across systems.Security and Compliance
a. Encryption and Data Privacy
• Azure Key Vault: A service for securely storing and accessing secrets, API keys, and certificates. It’s essential for keeping sensitive data safe, like API keys for email/SMS services.
• JWT (JSON Web Tokens): Secure data transmission and authentication across the system.
b. GDPR and Compliance
• Data Loss Prevention (DLP): A toolset to prevent the inadvertent sharing of sensitive user information, ensuring that your notification system complies with regulations like GDPR.
• Compliance Manager: A tool within Azure that helps manage compliance and track regulatory requirements across your system.DevOps and Deployment
a. Continuous Integration and Delivery
• Azure DevOps / GitHub Actions: These tools automate the build, testing, and deployment of your notification engine. They ensure that new features or fixes are rolled out seamlessly.
• Docker: Containerization ensures that your notification engine can run consistently across different environments.
• Kubernetes: For scaling your application and managing containerized workloads, Kubernetes is a powerful tool.
b. Monitoring and Alerts
• Azure Monitor: This service can be used to track the performance and availability of your application, alerting you when issues occur.
Questions to the Prod. & Buss. StakesBusiness and Functional Requirements
Notification Types
o What types of notifications are required? (e.g., transactional, promotional, critical alerts)
o Are there any specific notifications that must not be batched?
o Are there SLA expectations for real-time notifications? (e.g., OTP delivery within 5 seconds)User Preferences
o What channels should users be able to opt in/out of? (e.g., Email, SMS, In-App)
o Should users be allowed to choose preferences per notification type? (e.g., promotional via email, transactional via SMS)
o Are there any default preferences for new users?Internationalization and Localization
o Should notifications support multiple languages? If yes, which ones?
o Are there region-specific compliance rules for certain channels? (e.g., SMS in Europe under GDPR, email in India under DND rules)Error Handling
o How should failed notifications be handled? (e.g., retries, fallback to another channel)
o Should there be any specific retry logic for each channel?Channels
Channel-Specific Requirements
o Are there preferred vendors for each channel? (e.g., SendGrid for email, Twilio for SMS)
o Are any additional channels expected in the future (e.g., WhatsApp, Push Notifications)?
o Are social media notifications intended for individual users, groups, or public feeds?Channel Behavior
o Are there rate-limiting concerns for any channel (e.g., SMS or social media)?
o Should notifications have channel fallbacks? For example:
Primary Channel: Email
Fallback Channel: SMS if email delivery fails.Notification Delivery
Scheduling
o Should the system support delayed or scheduled notifications? (e.g., reminders, promotions)
o Are there any specific time zones or business hours for sending notifications?
o Should the system restrict delivery during certain hours (e.g., avoid sending SMS at night)?Prioritization
o How should notifications be prioritized? (e.g., OTPs > Payment Updates > Marketing)
o Should priorities be enforced across channels or per channel?Batching
o Should batch notifications be configurable by notification type or user?
o Are there size or frequency constraints for batch processing? (e.g., 100 notifications per batch every hour)Templates and Content
Template Management
o Should templates be reusable across channels or specific to each channel?
o Who is responsible for creating and maintaining templates? (e.g., marketing team or developers)
o Should templates support dynamic placeholders (e.g., {UserName}, {OrderId})?Content Personalization
o Are there rules for personalized content? (e.g., gender-specific language, order history)
o Should notifications include dynamic URLs (e.g., deep links for in-app)?Regulatory Compliance
o Are there compliance requirements for notification content? (e.g., opt-out links in emails, sender details in SMS)?
o Should users have the ability to request their notification history (audit/compliance)?Tracing and Analytics
Tracking and Logging
o What events need to be tracked? (e.g., sent, delivered, opened, clicked, failed)
o Should tracing support debugging for individual notifications (e.g., message ID lookup)?
o Are logs subject to any retention policies?Analytics
o What metrics are important for stakeholders? (e.g., delivery success rate, open rate, CTR)
o Should analytics be real-time or aggregated periodically?
o Are there specific dashboards required for business users?Scalability and Extensibility
Scalability
o What is the expected notification volume at launch and in the future? (e.g., 10,000 notifications/day scaling to 1M/day)
o Are there any seasonal peaks (e.g., marketing campaigns, festival periods)?
o Should the system support multi-tenancy (e.g., multiple brands under Indigo)?Extensibility
o Are there plans to add new notification types or channels in the future?
o Should the system be able to onboard new business services easily?Security and Compliance
Security
o Should sensitive data (e.g., user info, payment details) in notifications be encrypted?
o Are there audit requirements for accessing user preferences or templates?Regulatory Compliance
o Are there specific regulations to comply with (e.g., GDPR, CAN-SPAM, TRAI)?
o Should notifications honor user preferences across all Indigo platforms (website, app)?Operational and Maintenance
Monitoring
o Who is responsible for monitoring notification delivery failures (e.g., operations, support)?
o Should the system include alerts for critical failures (e.g., email provider outage)?Maintenance
o How often will templates, preferences, or configurations change?
o Are there DevOps expectations for CI/CD pipelines or disaster recovery?User Experience
Fallback Experience
o If notifications fail to deliver across all channels, how should the system respond?
Retry later?
Notify the user of failure via app or support?User Control
o Should users have access to notification history (e.g., inbox in the app)?
o Should users receive confirmations when they change preferences?
This content originally appeared on DEV Community and was authored by Jaydeep Kumar Sahu
Jaydeep Kumar Sahu | Sciencx (2025-01-23T15:34:06+00:00) Guide to Implement Push Notification Engine. Retrieved from https://www.scien.cx/2025/01/23/guide-to-implement-push-notification-engine/
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