Food Delivery App System Design

Requrirements

Functional Requirements:
1. Customers can search/browse restaurants and menus (by location, cuisine), place an order, and track it in real time until delivery.
2. Restaurants can receive/accept orders, and delivery partners can be assigned and matched to orders based on proximity.
Non-Functional Requirements:
1. High Availability: No single point of failure; system stays up during node/AZ failures (target 99.99%).
2. Low Latency: Search, order placement, and live location updates respond in tens-to-low-hundreds of ms.
3. Scalability: Handle spiky traffic (lunch/dinner peaks) and horizontal growth in users, restaurants, and cities.

HLD

Block Diagram

          flowchart LR

subgraph Client
A[Mobile App]
end

subgraph Edge
B[API Gateway]
end

subgraph Core Services
C[Order Service]
D[Payment Service]
E[Restaurant Service]
F[Rider Service]
G[Notification Service]
H[Location Service]
end

subgraph External
I[Payment Gateway]
J[Kafka]
K[Push Notification]
end

subgraph Databases
L[(Order DB)]
M[(Payment DB)]
N[(Restaurant DB)]
O[(Rider DB)]
P[(Location Redis)]
Q[(Notification DB)]
end

A -->|HTTPS| B
B --> C

C -->|HTTP Create Payment| D
D -->|HTTPS| I
I --> D
D -->|Payment Success| C

C -->|Publish OrderCreated| J

J --> E
J --> F
J --> G

E -->|RestaurantAccepted/FoodPreparing/FoodReady| J

F -->|RiderAssigned/PickedUp| J

H --> P
H --> G

J --> C

G --> K
K --> A

C --> L
D --> M
E --> N
F --> O
H --> P
G --> Q

Flow Diagram

sequenceDiagram

participant App
participant API as API Gateway
participant Order as Order service
participant Payment as Payment service
participant Gateway
participant Kafka
participant Restaurant as Restaurant service
participant Rider as Rider service
participant Notify as Notify service
participant Location as Location service

App->>API: POST /orders

API->>Order: Create Order

Order->>Order: Save Order(PAYMENT_PENDING)

Order->>Payment: HTTP Create Payment(orderId, amount)

Payment->>Gateway: Charge Customer

Gateway-->>Payment: Payment Success

Payment-->>Order: Payment Success

Order->>Order: Update PAYMENT_SUCCESS

Order->>Kafka: Publish OrderCreated

Kafka->>Restaurant: OrderCreated

Restaurant->>Restaurant: Validate Inventory

Restaurant->>Kafka: RestaurantAccepted

Kafka->>Order: RestaurantAccepted

Order->>Order: Status=ACCEPTED

Restaurant->>Kafka: FoodPreparing

Kafka->>Order: FoodPreparing

Order->>Order: Status=PREPARING

Kafka->>Rider: OrderCreated

Rider->>Rider: Find Nearest Rider

Rider->>Kafka: RiderAssigned

Kafka->>Order: RiderAssigned

Order->>Order: Save RiderId

Kafka->>Notify: RiderAssigned

Notify->>App: Push Notification

Restaurant->>Kafka: FoodReady

Kafka->>Order: FoodReady

Order->>Order: Status=READY

Kafka->>Rider: FoodReady

Rider->>Restaurant: Pickup

Rider->>Kafka: PickedUp

Kafka->>Order: PickedUp

Order->>Order: Status=PICKED_UP

Location->>Notify: Rider GPS Updates

Notify->>App: Live Rider Location

Rider->>Kafka: Delivered

Kafka->>Order: Delivered

Order->>Order: Status=DELIVERED

Kafka->>Notify: Delivered

Notify->>App: Order Delivered

Kafka Topics

OrderCreated
RestaurantAccepted
FoodPreparing
FoodReady
RiderAssigned
PickedUp
Delivered
Cancelled
PaymentFailed

DB Schema


Order Database
orders table
-----------------------------
order_id (PK)
customer_id
restaurant_id
payment_status
order_status
total_mount
rider_id
delivery_address
created_at
updated_at

order_items
--------------------------
id (PK)
order_id (FK)
menu_item_id
quantity
price
special_instruction

PAYMENT DATABASE
payments table
--------------------------
payment_id
order_id
customer_id
amount
gateway
gateway_transaction_id
status
created_at

RESTURANTS DATABASE
restaurants table
-------------------
restaurant_id
name
address
rating
latitude
longitude

menu_items table
-----------------------
menu_item_id
restaurant_id
name
price
available
category

inventory table
--------------------
menu_item_id
available_quantity
reserved_quantity

RIDER DATABASE
riders table
-----------------------
rider_id
name
phone
rating
vehicle
status
current_latitude
current_longitude

rider_assignments table
---------------------
order_id
rider_id
assigned_at
pickup_time
delivery_time

NOTIFICATION DB
notifications table
----------------------
notification_id
customer_id
order_id
title
body
status
created_at

LOCATION DATABASE
GEOADD riders
rider_id
latitude
longitude