Notification to all parties in LLD - Architecture Diagram

System Overview - Notification to all parties

This system sends notifications to all relevant parties efficiently and reliably. It supports multiple notification channels like email, SMS, and push notifications, ensuring messages reach users promptly.

Architecture Diagram

User
  |
  v
Load Balancer
  |
  v
API Gateway
  |
  v
Notification Service
  |           |           |
  v           v           v
Email Service SMS Service Push Service
  |           |           |
  v           v           v
Email Server  SMS Gateway Push Server
  |
  v
Database
  |
  v
Cache

Components

User

client

Initiates notification requests

Load Balancer

load_balancer

Distributes incoming requests evenly to API Gateway instances

API Gateway

api_gateway

Routes requests to Notification Service and handles authentication

Notification Service

service

Processes notification requests and sends to appropriate channel services

Email Service

service

Formats and sends email notifications

SMS Service

service

Formats and sends SMS notifications

Push Service

service

Formats and sends push notifications

Email Server

external_service

Delivers emails to recipients

SMS Gateway

external_service

Delivers SMS messages to recipients

Push Server

external_service

Delivers push notifications to devices

Database

database

Stores user contact info and notification logs

Cache

cache

Stores frequently accessed user data for faster retrieval

Request Flow - 17 Hops

User → Load Balancer

Load Balancer → API Gateway

API Gateway → Notification Service

Notification Service → Cache

Cache → Notification Service

Notification Service → Database

Database → Notification Service

Notification Service → Email Service

Notification Service → SMS Service

Notification Service → Push Service

Email Service → Email Server

SMS Service → SMS Gateway

Push Service → Push Server

Notification Service → Database

Notification Service → API Gateway

API Gateway → Load Balancer

Load Balancer → User

Failure Scenario

Component Fails:Database

Impact:Notification service cannot retrieve or log user info; notifications may be delayed or incomplete

Mitigation:Use cache for reads to serve recent user info; queue logs for later retry; implement database replication for high availability

Architecture Quiz - 3 Questions

Which component is responsible for distributing incoming user requests evenly?

A Notification Service

B Load Balancer

C API Gateway

D Cache

Design Principle

This design uses layered components to separate concerns: load balancing for traffic distribution, API gateway for routing and security, a dedicated notification service for processing, and specialized channel services for delivery. Caching improves performance by reducing database load. The system supports multiple notification channels and logs activity for reliability.

Practice

1.

What is the main purpose of a notification system that sends messages to all parties?

easy

A. To quickly share important messages with everyone involved

B. To store large amounts of data securely

C. To perform complex calculations on user data

D. To create user profiles and preferences

Solution

1. Step 1: Understand the role of notifications

   Notifications are designed to deliver messages to users or parties quickly and efficiently.

2. Step 2: Identify the main goal

   The main goal is to share important information with all involved parties without delay.

3. Final Answer:

   To quickly share important messages with everyone involved -> Option A

4. Quick Check:

   Notification purpose = quick message sharing [OK]

Hint: Notifications = fast message delivery to all involved [OK]

Common Mistakes:

• Confusing notifications with data storage
• Thinking notifications perform data processing
• Assuming notifications create user profiles

2.

Which of the following is the correct way to represent a notification service that sends messages to all parties in pseudocode?

function notifyAll(parties, message) {
  for (let i = 0; i < parties.length; i++) {
    parties[i].send(message);
  }
}

easy

A. Call send(message) once without looping

B. Send message only to the first party

C. Loop through parties and call send(message) on each

D. Loop through parties but do not send any message

Solution

1. Step 1: Analyze the pseudocode loop

   The code loops through each party in the parties list using a for loop.

2. Step 2: Check the send method call

   Inside the loop, it calls send(message) on each party, ensuring all get notified.

3. Final Answer:

   Loop through parties and call send(message) on each -> Option C

4. Quick Check:

   Loop + send call = notify all [OK]

Hint: Loop through all parties to send message [OK]

Common Mistakes:

• Sending message only once
• Not looping through all parties
• Calling send outside the loop

3.

Consider this code snippet for notifying parties:

parties = ["Alice", "Bob", "Charlie"]
function notifyAll(parties, message) {
  let notified = []
  for (const person of parties) {
    notified.push(person + ": " + message)
  }
  return notified
}

console.log(notifyAll(parties, "Meeting at 5 PM"))

What will be the output?

medium

A. ["Alice: Meeting at 5 PM", "Bob: Meeting at 5 PM", "Charlie: Meeting at 5 PM"]

B. ["Meeting at 5 PM", "Meeting at 5 PM", "Meeting at 5 PM"]

C. ["Alice", "Bob", "Charlie"]

D. Error: notifyAll is not defined

Solution

1. Step 1: Understand the loop behavior

   The function loops over each person in parties and creates a string combining their name and the message.

2. Step 2: Check the returned list

   The notified list contains strings like "Alice: Meeting at 5 PM" for each party.

3. Final Answer:

   ["Alice: Meeting at 5 PM", "Bob: Meeting at 5 PM", "Charlie: Meeting at 5 PM"] -> Option A

4. Quick Check:

   Loop + string concat = list of personalized messages [OK]

Hint: Each party gets message with their name prefixed [OK]

Common Mistakes:

• Returning only messages without names
• Returning original party list
• Assuming function is undefined

4.

Identify the bug in this notification function and select the fix:

function notifyAll(parties, message) {
  for (let i = 0; i < parties.length; i++) {
    parties.send(message)
  }
}

medium

A. Remove the loop and call parties.send(message) once

B. Add a return statement inside the loop

C. Change i < parties.length to i <= parties.length

D. Change parties.send(message) to parties[i].send(message)

Solution

1. Step 1: Identify incorrect method call

   The code calls send on the entire parties array instead of individual party objects.

2. Step 2: Fix by indexing the array

   Use parties[i].send(message) to call send on each party in the loop.

3. Final Answer:

   Change parties.send(message) to parties[i].send(message) -> Option D

4. Quick Check:

   Call send on each party object [OK]

Hint: Call send on parties[i], not parties array [OK]

Common Mistakes:

• Calling send on the whole array
• Using wrong loop condition
• Adding unnecessary return inside loop

5.

You are designing a notification system to alert all parties involved in a project. Which design choice best ensures scalability and reliability?

• A. Use a single server to send notifications sequentially to all parties.
• B. Send notifications only to a random subset of parties to reduce load.
• C. Store all notifications in a database and send them manually when needed.
• D. Use a message queue to distribute notification tasks to multiple worker servers.

hard

A. Single server sending sequentially

B. Message queue with multiple workers

C. Store notifications and send manually

D. Send to random subset to reduce load

Solution

1. Step 1: Evaluate single server approach

   Sending sequentially from one server limits scalability and can cause delays or failures.

2. Step 2: Consider message queue with workers

   Using a message queue allows distributing notification tasks to multiple workers, improving scalability and reliability.

3. Step 3: Assess other options

   Storing notifications for manual sending is slow; sending to random subset misses parties.

4. Final Answer:

   Message queue with multiple workers -> Option B

5. Quick Check:

   Queue + workers = scalable, reliable notifications [OK]

Hint: Use queues and workers for scalable notifications [OK]

Common Mistakes:

• Relying on single server for all notifications
• Sending notifications manually
• Skipping parties to reduce load