This course immerses the learner into the design of systems and makes them ready for any new design problems.

sys-design.tar.gz

basic

This course provides an alternate perspective to system design where we learn about building blocs first and then use them to build bigger, more capable systems.

Copy-System Design-The Missing Pieces

Let's start with the high-level design of a map system. We split the discussion into two sections:
1. The services we will need in our design.
2. The workflow that interconnects these services.
## Services
Following are the services we will use in our design:
* **Location finder**: It is hard for us to remember the latitude/longitude for every place, we couldn't determine where are we standing. The location finder is a service used to find the user's current location and show it on the map.
* **Route finder**: For the people who are new to a place, it is difficult to travel because they don't know the paths. The route finder is a service used to find the paths between two points (locations).
* **Navigator**: Suggesting a route through the route finder is not enough. A user may deviate from the optimal path. In that case, a navigator service is used. This service keeps track of users' journeys and sends updated directions and notifications to the users as soon as they deviate from the suggested route.
* **GPS/Wifi/Cellular technology**: These are the technologies that we used to find the ground position of the user.
* **Distributed search**: For converting place names to latitude/longitude values, we need a conversion system behind the source and destination fields. Distributed search maintains an index consisting of places names and their mapping to latitude and longitude. User's search keywords/#key# terms: See Distributed Search for details. #key# are searched using this service to find a location on the map.
* **Area search service**: The area search service coordinates between the distributed search and graph processing service to obtain the shortest path against a user query. The area search service will request the distributed search to obtain the locations of the source and destination on the map. Then, it will use the graph processing service to find the optimal path from the source to the destination.
* **Graph processing service**: There can be multiple paths from one place to another; how can we decide which path to follow. It is a service that is used to run the shortest path algorithm on a shorter graph based on the area spanning the source and destination points.
* **Database**: As discussed in the previous lesson, we have all the roads data from various sources that is stored in the form of a graph. We will map this data on a database to develop the road network graph. We are using a graph database (like the DataStax graph DB) to store the graph for our design.
* **Pub-sub system**: The users can deviate from the suggested path, in that case, they want to know the new path. Pub-sub is a system that listens to various events from a service and triggers another service accordingly. For example, when a user deviates from the suggested path, it pings the *area search service* to find the route again from the user's current location and the destination point. It also collects the streams of location data for different users from the navigator. This data can be processed later to find traffic patterns on different roads at different times. We used Kafka as a pub-sub system in our design.
* **Third-party roads data**: How can we build a map system if we don't have the road networks data? It is a service that collects the road data from third-party resources and preprocesses the collected data to bring it into a single format that can be utilized to build the graph.
* **Graph building**: It is a service that builds the graph from the given data, either collected from the third-party resources or from the users.
* **User**: It is a person or a program that uses the services of the map system.
* **Load balancer**: It is a system that is used to distribute user requests among different servers and services.

Below is an illustration that shows how the above components are connected.

Let's build a high-level design of maps service.

Design of Google Maps

High-level design

Services