vipentti / ex-5-amqp

exercise 5 message queue

Exercise 5 message queue

• Author: Ville Penttinen

An implementation of the message queue exercise for COMP.SE 140.

Requirements

• Docker

Purpose

To demonstrate the ability to publish messages into a message queue utilizing C# and RabbitMQ.

Original publishes messages in the form of MSQ_<NR> where number is an incrementing number starting from 1 to the topic my.o.

Intermediate listens subscribes to listen to my.o and then when a message is received Intermediate sends a new message in the format Got <the received message> to the topic my.i

Observer subscribes to both topics my.o and my.i, when it receives a message it writes into a file. This file can be found locally, by default in .shared_volume/message.txt after running the application.

HttpServer is a simple http server, which listens to a GET request and then reads the contents of the file written to by Observer and returns the contents of that file.

Getting started

1. Clone the repository
2. Navigate into the folder and run

   docker-compose up --build -d
   

   • This may take a while the first time
3. Wait for up to 30 seconds
4. Then run

   curl http://localhost:8080
   

This should return response similiar to:

2020-10-19T19:10:12.9517147Z Topic my.o: MSG_1
2020-10-19T19:10:13.9489234Z Topic my.i: Got MSG_1
2020-10-19T19:10:15.9460544Z Topic my.o: MSG_2
2020-10-19T19:10:16.9507742Z Topic my.i: Got MSG_2
2020-10-19T19:10:18.9478337Z Topic my.o: MSG_3
2020-10-19T19:10:19.9498052Z Topic my.i: Got MSG_3

Benefits of topic-based communication

• A single message sent to a topic may be read by multiple listeners
• Listener may subscribe to multiple topics
• Publishers and subscribers are loosely coupled
• Publishers may simply send messages to the specific topic without having to know about subscribers

What I learned from this exercise

• Improved understanding of RabbitMQ
• How to utilize RabbitMQ's C#-client
• How to setup a shared docker volume where file written to by one container may be read by another
• Improved understanding of topic-based communication

Structure

src/Common

Common and shared functionality

src/Original

This service starts up, connects to the RabbitMQ instance and then starts sending messages. The service sends total of 3 messages with a 3 second delay between each message.

src/Intermediate

Listens for the messages sent by Original, then waits for 1 second before sending a message to its own topic.

src/Observer

Listens for messages from both Original and Intermediate, writes them to the file OutFilePath. By default when running with docker-compose the OutFilePath is set to a shared volume which is mounted to .shared_volume/ locally.

src/HttpServer

Very basic http server which simply reads the file written by Observer when a http request is made. By default listens for http://localhost:8080.