Emergency handling in LLD - Architecture Diagram

System Overview - Emergency handling

This system manages emergency situations by receiving alerts from users or sensors, processing them quickly, and dispatching appropriate responders. It must handle high volumes of requests reliably and ensure timely communication to save lives.

Architecture Diagram

User/Sensor
   |
   v
Load Balancer
   |
   v
API Gateway
   |
   v
Emergency Service
  /    \
 v      v
Cache   Message Queue
  |        |
  v        v
Database  Notification Service
            |
            v
       Responder Devices

Components

User/Sensor

client

Initiates emergency alerts or status updates

Load Balancer

load_balancer

Distributes incoming requests evenly to prevent overload

API Gateway

api_gateway

Routes requests to the emergency service and handles authentication

Emergency Service

service

Processes emergency alerts, checks cache, and triggers notifications

Cache

cache

Stores recent emergency data for quick access

Message Queue

queue

Manages asynchronous notification tasks to responders

Database

database

Stores persistent emergency records and user data

Notification Service

service

Sends alerts to responder devices asynchronously

Responder Devices

client

Receive emergency notifications and respond accordingly

Request Flow - 9 Hops

User/Sensor → Load Balancer

Load Balancer → API Gateway

API Gateway → Emergency Service

Emergency Service → Cache

Emergency Service → Database

Emergency Service → Message Queue

Message Queue → Notification Service

Notification Service → Responder Devices

Emergency Service → Load Balancer

Failure Scenario

Component Fails:Database

Impact:New emergency alerts cannot be stored persistently; historical data access is unavailable

Mitigation:System continues to serve from cache for recent emergencies; alerts are still processed and notifications sent; database replication and failover restore service quickly

Architecture Quiz - 3 Questions

Which component ensures that incoming emergency alerts are distributed evenly to prevent overload?

A Cache

B API Gateway

C Load Balancer

D Message Queue

Design Principle

This architecture uses caching to speed up repeated emergency data access and a message queue to handle notifications asynchronously, ensuring the system remains responsive and scalable under high load.

Practice

1. What is the primary goal of an emergency handling system in system design?

easy

A. To detect problems quickly and protect people and property

B. To increase system performance under normal conditions

C. To reduce the cost of hardware components

D. To provide detailed analytics for marketing purposes

Solution

1. Step 1: Understand the purpose of emergency handling

   Emergency handling systems are designed to detect issues fast and act to prevent harm.

2. Step 2: Identify the main goal

   The main goal is to protect people and property by quick detection and response.

3. Final Answer:

   To detect problems quickly and protect people and property -> Option A

4. Quick Check:

   Emergency handling = fast detection and protection [OK]

Hint: Focus on safety and speed in emergencies [OK]

Common Mistakes:

• Confusing emergency handling with performance optimization
• Thinking it is about cost reduction
• Assuming it is for marketing analytics

2. Which component is NOT typically part of an emergency handling system?

easy

A. Safety action controller

B. Alerting system

C. Detection module

D. User interface for marketing

Solution

1. Step 1: List typical components

   Emergency handling systems usually have detection, alerting, safety actions, and logging.

2. Step 2: Identify the unrelated component

   User interface for marketing is unrelated to emergency handling functions.

3. Final Answer:

   User interface for marketing -> Option D

4. Quick Check:

   Marketing UI ≠ emergency handling component [OK]

Hint: Exclude marketing from emergency system parts [OK]

Common Mistakes:

• Including unrelated business components
• Confusing alerting with marketing notifications
• Ignoring safety action controllers

3. Consider this simplified emergency system flow:
if sensor.detect(): alert.send(); safety.activate(); log.record()
What happens if sensor.detect() returns false?

medium

A. Alert, safety, and log actions all execute

B. Only alert and safety actions execute

C. No actions execute

D. Only log action executes

Solution

1. Step 1: Analyze the if condition

   The actions alert.send(), safety.activate(), and log.record() run only if sensor.detect() is true.

2. Step 2: Determine behavior when sensor.detect() is false

   If sensor.detect() returns false, the code block inside if does not run, so no actions execute.

3. Final Answer:

   No actions execute -> Option C

4. Quick Check:

   False detection = no emergency actions [OK]

Hint: If condition false means skip all inside actions [OK]

Common Mistakes:

• Assuming log always runs regardless of detection
• Thinking alert or safety run without detection
• Confusing else behavior when none is given

4. In an emergency system, this code snippet causes a problem:
if sensor.detect():
alert.send()
safety.activate()
log.record()
What is the main issue?

medium

A. Missing indentation causes log.record() to run always

B. safety.activate() is outside the if block

C. alert.send() is not called properly

D. log.record() runs even if no detection

Solution

1. Step 1: Check code indentation

   log.record() is not indented under the if, so it runs always.

2. Step 2: Understand impact

   log.record() runs even when sensor.detect() is false, which is incorrect behavior.

3. Final Answer:

   Missing indentation causes log.record() to run always -> Option A

4. Quick Check:

   Indentation controls conditional execution [OK]

Hint: Indent all emergency actions inside detection check [OK]

Common Mistakes:

• Ignoring indentation importance
• Assuming all lines are inside if by default
• Confusing which lines run conditionally

5. You design an emergency system that must alert multiple teams and log events reliably. Which design approach best ensures alerts are sent even if one alert service fails?

hard

A. Send alerts sequentially and stop on first failure

B. Send alerts in parallel with retries and fallback logging

C. Send alerts only to the primary team to reduce complexity

D. Log events only after all alerts succeed

Solution

1. Step 1: Understand reliability needs

   To ensure alerts reach multiple teams, sending in parallel avoids blocking on one failure.

2. Step 2: Use retries and fallback logging

   Retries help recover from temporary failures; fallback logging records failures for later review.

3. Final Answer:

   Send alerts in parallel with retries and fallback logging -> Option B

4. Quick Check:

   Parallel + retries = reliable alerting [OK]

Hint: Use parallel alerts with retries for reliability [OK]

Common Mistakes:

• Stopping alerts on first failure
• Ignoring retries and fallback mechanisms
• Reducing alert recipients to simplify