This is a class project for CIS 505 Software Systems (Fall 2020) at University of Pennsylvania.
PennCloud is a distributed cloud platform, with webmail service similar to Gmail, and a storage service similar to Google Drive. This project is built in C++, with Protobuf used for data serialization, gRPC used for communication between components and React for frontend applications. See each component and its features below:
Clients are directed to one of multiple frontend servers through a load balancer. Each frontend server periodically send a ping message to the frontend load balancer which keeps track of all frontend servers and their status.
The frontend servers provide interfaces for webmail service and storage service for each user account.
A special admin console page shows status of all frontend, backend servers and a way to view all key-value pairs stored in the BigTable.
Each frontend server also serves as a backend client with an interface to access storage operations in the backend servers. To make our application more robust, we built support for data replication, load balancing, checkpointing and recovery.
Health check: A single backend master node keeps track of all backend server status (using a pinging service similar to frontend load balancer keeping track of frontend servers).
Load Balancing: Each new backend client (frontend server) is assigned a backend server with the least load (fewest data entries). The backend client caches the address of the backend server for further requests.
Quorum Replication: We implement quorum replication for stronger fault tolerance. To minimizing losing data in case a server dies, we write data to all healthy servers; and for faster read, we contact half of the healthy servers to get the data.
Local Checkpointing & Recovery: The backend server node has its own BigTable storage, all changes are in memory and stored in a log file for each operation. It periodically dumps key-value pairs in memory to the local storage file (checkpointing). When a node fails, the backend master sends the failed node’s address to a healthy node who sends its recovery file.