Distributed Filesystem (ISU CS454 - Distributed Systems, 2021)

A program designed to emulate a distributed filesystem, supporting multiple client connections to primary server, with persistence to backup servers.

Client

Upon connecting to a primary server, a client is allowed 3 basic operations:

• OPEN - download file from server to requesting client. If the file does not exit in primary server, primary server requests file from backup servers if it exits. Upon success, primary server will copy file from backup to primary, and send it to the requesting client.
• ADD - upload file from requesting client to primary server and all backup servers.
• REMOVE - delete file from requesting client, primary server, and backup servers.

A client may also connect to a backup server, but its changes will not be persisted to the primary server and other backup servers. A client must log in with an existing username and password. For the purposes of this documentation, username admin and password coms454 is used. admin may create new username and passwords. See "Adding New Users" under "Running Instructions".

There is no limit set on the number of client connections to servers.

Server

A server can either be a backup server or a primary server. A primary server will maintain consistency across the backup servers. A primary server must be running in order for a backup server to run and connect to the primary, as well as for clients to connect to it. A new backup server may connect to the primary server at any time.

Running Instructions

To compile, run javac *.java in every subdirectory. For example:

cd distributed_filesystem/Server
javac *.java

Setting up Connections

Note: Because everything is designed to run on localhost, differnet folders must be used for each client and server instance in order to demonstrate full functionality. Hence, this repository contains a Server folder for primary server, Client for client connection, and Backup1 and Backup2 for the backupservers.

Firstly, run the primary server with a chosen port:

nikababtsov@LAPTOP-VGHR5LTP:/mnt/c/Users/Nika/distributed_filesystem/Server$ java Server 5000
Primary Server started
Waiting for a client ...

---

Then, run the backup server from Backup1, choosing a different port and specifying the previously chosen port of the primary server:

nikababtsov@LAPTOP-VGHR5LTP:/mnt/c/Users/Nika/distributed_filesystem/Backup1$ java Server 5001 5000
Just send out: JOIN 5001 to port: 5000
Got response: COMPLETE_JOIN
Backup with port 5001 is up and listening for primary

Primary server should say:

Got message: JOIN 5001
Just had backup server join on port 5001

Then, connect to the primary server as a client:

nikababtsov@LAPTOP-VGHR5LTP:/mnt/c/Users/Nika/distributed_filesystem/Client$ java Client 5000
Enter username: 
admin
Enter password: 
coms454
Welcome user
Type OPEN <filename> to retrieve file, ADD <filename> to add new file, REMOVE <filename> to remove it
>

Primary server should say: Got message: TEST admin coms454

Client Operations

upload a file to primary and backup servers

>ADD exampleClientFile.txt
File sent to server

Primary server should say:

Got message: ADD exampleClientFile.txt
Attemtping to recieve file...
exampleClientFile.txt
File exampleClientFile.txt downloaded!
File received!

Backup server should say:

Backup got message: ADD exampleClientFile.txt
exampleClientFile.txt
File exampleClientFile.txt downloaded!
File Received

exampleClientFile.txt should appear under distributed_filesystem/Backup1/ and distributed_filesystem/Server/

download a file from primary or backup servers:

OPEN exampleServerFile.txt
File exampleServerFile.txt downloaded!

and exampleServerFile.txt should appear under distributed_filesystem/Client/

Primary server should say:

Got message: OPEN exampleServerFile.txt
Attemtping to sending file...
exampleServerFile.txt
File sent to client
File sent!

remove a file from primary and backup servers

>REMOVE exampleClientFile.txt
File exampleClientFile.txt removed locally
File exampleClientFile.txt deleted from primary and backups successfully

primary server should say:

Got message: REMOVE exampleClientFile.txt
File exampleClientFile.txt deleted from primary
File exampleClientFile.txt deleted from all backups

backup server should say:

Backup got message: REMOVE exampleClientFile.txt

exampleClientFile.txt should disappear from under distributed_filesystem/Server/, distributed_filesystem/Backup1/, and distributed_filesystem/Client/

Adding New Users

Usernames are stored in a plain textfile distributed_filesystem/Server/users.txt, passwords are hashed and stored in distributed_filesystem/Server/security.txt

To add a new user, run:

nikababtsov@LAPTOP-VGHR5LTP:/mnt/c/Users/Nika/distributed_filesystem/Server$ java AddUser coms454
New username:
newuser123 
Password:
newuserpass
Confirm Password
newuserpass
Added

The users.txt and security.txt will be updated accordingly, and these user credentials may now be used to log in for client connections