Distributed-Banking-System

gRPC Written Report

Problem Statement

Design and implement a distributed banking application usiing gRPC as the communication mechanism implementing a “read-your-writes” consistency mechanism.

Goal

The goal is to implement a distributed banking application that uses gRPC for the communication mechanism while ensuring a good level of consistency accross all the replicas. The idea is to implement “read-your-writes” consistency model and ensure consistency.

Setup

Languages used are: Golang as the programming language
gRPC and Protocol Buffers as the communication mechanism

Setup:
Installation and setup of Go on Ubuntu:

Go version used: 1.21.3

1. Go to the link and follow the steps https://go.dev/doc/install 

Step 1 is to download the Go package for Linux from https://go.dev/dl/ 

1.   sudo rm -rf /usr/local/go && sudo tar -C /usr/local -xzf go1.21.3.linux-arm64.tar.gz

2.  export PATH=$PATH:/usr/local/go/bin

3.  go version

Implementation Processes

There are three main code files which cover the entire functionality

1. branch.go it contains all the implementations of the methods like Deposit, Withdraw, Propagate_Withdraw, Propagate_Deposit.

2. branch.proto contains the gRPC protobuffer related stuff for the services and return types.

3. customer_service.go: It reads the input data json file and processes the customer’s events sequentially.

4. start_branch_servers.go: This code spawns the branch servers after reading the branches data from the input file.

   First step is to run start_branch_servers.go, it expects the input data file name to be the command line argument

   Link to input_data.json

   Eg usage:

   go run start_branch_servers.go input_data.json
   

   In the second terminal tab, run the customers

  cd customer_service

  go run customer_service.go ../input_data.json

I have implemented the “read-your-writes” consistency model by following the steps below:

1.Event unique token generation: When the customer initiates an event/transaction processing, this unique “token” which in my implementation is the unique ID of the current event is sent to the Write operation which is “DEPOSIT” or “WITHDRAW” operation of a branch.

2.Token Propagation: The passed token from the customer process to the branch process will be used to send to the respective peer branches while sending the propagation requests. This way each branch process stores the information in a map called writeEventsReceived, and this is used to determine whether to block an incoming read request from the customer.

The following code represents the part where the process blocks the read request from a customer until it knows that the previous write operation has managed to propagate to this current branch.

func (s *BranchServer) QueryBalance(ctx context.Context, request *branch.QueryBalanceRequest) (*branch.QueryBalanceResponse, error) {

var lastWriteEventID int32 = request.LastWriteEventID

if lastWriteEventID == -1 {
// Return the current balance, since it's the first query
// represented by EventID = -1
return &branch.QueryBalanceResponse{
Balance: s.Balance,
}, nil
}
for !s.IsEventIDExists(lastWriteEventID) {
time.Sleep(100 * time.Millisecond) // Wait for a short duration
}

// Return the current balance
return &branch.QueryBalanceResponse{
Balance: s.Balance,
}, nil

}