This comprehensive course prepares you for DoorDash software engineer interviews and DoorDash system design interview questions.

This course prepares you for a system design interview by using a case study of DoorDash (a prepared food delivery system) and familiarizes you with the challenges you will encounter during the interview. 

You will begin by understanding the theory behind the system design interview to give you an idea of what to expect. Next, you’ll understand how to identify a system’s requirements, handle data, and lay down the architecture of the system. Along the way, diagrams and quizzes will help you solidify your concepts.

By the end of this course, you will have a solid understanding of how to approach a system design interview, and you will have the confidence to answer a number of different scenarios, no matter the question.

System Design Interview: DoorDash

## Order fulfilment workflow
Let's first define some acronyms which we will be using later on:
* Ordering Service: **OS**
* Order Fulfilment Service: **OFS**
* Notification Service: **NS**
* DoorDasher Dispatch Service: **DDS**
* Message: **MSG**



### Order workflow explained
Once the customer places an order using the mobile/web client using the OS, the order processing workflow could be as follows:
1. **OS** publishes a `MSG(#1)` to the queue about the order so that the downstream services can start processing.
2. **NS** reads `MSG(#1)` and notifies the corresponding restaurant and the customer that an order is placed and pending their acceptance.
3. Once the order is accepted by the restaurant, using the OFS, the **OFS** will publish a `MSG(#2)` to the queue regarding the acceptance of the order.
4. **DDS** will read the `MSG(#2)` and post an area-specific `MSG(#3)` to the queue. DDS could also auto-assign an order to an available DoorDasher, and in which case, it will post a related MSG.
5. **NS** will read `MSG(#2)` and notify the customer that the restaurant accepted the order.
6. **NS** will read `MSG(#3)` and notify the DoorDashers in the area about the availability of the order to process their acceptance.
7. The DoorDasher will accept the order using DDS. **DDS** will then post a `MSG(#4)` to the queue about DoorDasher assignment/acceptance.
8. **NS** will read `MSG(#4)` and notify the customer and the restaurant about the DoorDasher assignment.
9. Once the food is ready to be picked up, the restaurant will update the status of the order using OFS. **OFS** will post a `MSG(#5)` to the queue that the food is ready to be picked up.
10. **NS** will read `MSG(#5)` and notify the assigned DoorDasher as well as the customer that the food is ready to be picked up.
11. After the DoorDasher picks up the food, the restaurant staff will update the status of the order using OFS. **OFS** will then post a `MSG(#6)` to the queue that the order has been picked up.
12. **NS** reads `MSG(#6)` and notifies the customer that the order is picked up.
13. DoorDasher reaches the customer,  delivers the food, and marks the order as complete! The food is here!! **DDS** posts a `MSG(#7)` to the queue about delivery completion.
14. **OFS** reads `MSG(#7)` and updates the status of the order to be completed.
15. **NS** reads `MSG(#7)` and notifies the restaurant and the customer about the delivery of food.

# Order fulfilment workflow
Let's first define some acronyms which we will be using later on:
* Ordering Service: **OS**
* Order Fulfilment Service: **OFS**
* Notification Service: **NS**
* DoorDasher Dispatch Service: **DDS**
* Message: **MSG**



## Order workflow explained
Once the customer places an order using the mobile/web client using the OS, the order processing workflow could be as follows:
1. **OS** publishes a `MSG(#1)` to the queue about the order so that the downstream services can start processing.
2. **NS** reads `MSG(#1)` and notifies the corresponding restaurant and the customer that an order is placed and pending their acceptance.
3. Once the order is accepted by the restaurant, using the OFS, the **OFS** will publish a `MSG(#2)` to the queue regarding the acceptance of the order.
4. **DDS** will read the `MSG(#2)` and post an area-specific `MSG(#3)` to the queue. DDS could also auto-assign an order to an available DoorDasher, and in which case, it will post a related MSG.
5. **NS** will read `MSG(#2)` and notify the customer that the restaurant accepted the order.
6. **NS** will read `MSG(#3)` and notify the DoorDashers in the area about the availability of the order to process their acceptance.
7. The DoorDasher will accept the order using DDS. **DDS** will then post a `MSG(#4)` to the queue about DoorDasher assignment/acceptance.
8. **NS** will read `MSG(#4)` and notify the customer and the restaurant about the DoorDasher assignment.
9. Once the food is ready to be picked up, the restaurant will update the status of the order using OFS. **OFS** will post a `MSG(#5)` to the queue that the food is ready to be picked up.
10. **NS** will read `MSG(#5)` and notify the assigned DoorDasher as well as the customer that the food is ready to be picked up.
11. After the DoorDasher picks up the food, the restaurant staff will update the status of the order using OFS. **OFS** will then post a `MSG(#6)` to the queue that the order has been picked up.
12. **NS** reads `MSG(#6)` and notifies the customer that the order is picked up.
13. DoorDasher reaches the customer,  delivers the food, and marks the order as complete! The food is here!! **DDS** posts a `MSG(#7)` to the queue about delivery completion.
14. **OFS** reads `MSG(#7)` and updates the status of the order to be completed.
15. **NS** reads `MSG(#7)` and notifies the restaurant and the customer about the delivery of food.

Understand the order processing workflow, API, and security of the system. 


Learn Order Fulfilment Workflow, System APIs & Security

Understand the order processing workflow, API, and security of the system.