___  ___                                ______           _             
|  \/  |                                | ___ \         | |            
| .  . | ___  ___ ___  __ _  __ _  ___  | |_/ /_ __ ___ | | _____ _ __ 
| |\/| |/ _ \/ __/ __|/ _` |/ _` |/ _ \ | ___ \ '__/ _ \| |/ / _ \ '__|
| |  | |  __/\__ \__ \ (_| | (_| |  __/ | |_/ / | | (_) |   <  __/ |   
\_|  |_/\___||___/___/\__,_|\__, |\___| \____/|_|  \___/|_|\_\___|_|   
                             __/ |                                     
                            |___/                                      

Message Broker and DNS Server

This project is an implementation of a distributed message broker system with a DNS server, inspired by the Advanced Message Queuing Protocol (AMQP). The system enables asynchronous communication between clients by managing message exchanges and queues while supporting leader election for fault tolerance.

Features

Figure 1: System Overview. For image source see Acknowledgements.

DNS Server

• Implements a Simple DNS Protocol (SDP) to register, unregister, and resolve domain names.
• Allows message brokers to register themselves at startup.
• Handles multiple simultaneous clients using multi-threading.
• Supports in-memory persistence for fast lookups.

Message Broker

• Implements a Simple Message Queuing Protocol (SMQP) for message routing.
• Supports direct, fanout, and topic exchanges to route messages efficiently.
• Enables subscribers to receive messages asynchronously.
• Handles leader election to determine the active broker in a distributed environment.

Getting Started

Prerequisites

• Java JDK 21
• Maven
• Netcat (Optional) for manual testing.

Installation

Clone the repository:

git clone git@github.com:tonyzamyatin/message-broker.git
cd message-broker

Compile the project:

mvn compile

Run the DNS Server:

mvn exec:java@dns-0

Run the Message Broker:

mvn exec:java@broker-0

Protocols

Simple DNS Protocol (SDP)

The DNS server provides domain name resolution for brokers.

Command	Description	Response Example
register <name> <ip:port>	Registers a domain name.	ok
resolve <name>	Resolves a domain name to IP and port.	192.168.1.10:8080
unregister <name>	Removes a domain registration.	ok

Simple Message Queuing Protocol (SMQP)

The message broker routes messages between clients.

Command	Description	Response Example
exchange <type> <name>	Creates an exchange (direct, fanout, topic).	ok
queue <name>	Declares a queue.	ok
bind <binding-key>	Binds a queue to an exchange.	ok
publish <routing-key> <msg>	Publishes a message with a routing key.	ok
subscribe	Subscribes to messages in a queue.	ok

Leader Election Protocol (LEP)

The system supports leader election to ensure high availability.

Command	Description	Response Example
elect <id>	Initiates an election.	ok
declare <id>	Declares a broker as the leader.	ack <sender-id>
ping	Leader sends heartbeat messages.	pong

Manual Testing

You can test the components manually using Netcat:

nc localhost 20000  # Connect to the Message Broker
nc localhost 18000  # Connect to the DNS Server

Class Diagram

Acknowledgment

This project is based on the assignments from the DS Lab of the Distributed Systems course at TU Wien during the winter semester 2024.

License

This project is open-source and available under the MIT License.

Author

Anton Zamyatin