CS6650 Spring 2022 Assignment 2

Building the Server

This assignment builds on assignment 1. Your client won’t change (unless it has a bug in it!). Your will implement processing logic in your server and post the result to a queue for subsequent processing.

Step 1 - Implement the Server

In this assignment, you will implement the doPost() method in your servlet to:

1. fully validate the URL and JSON payload
2. if valid, format the incoming data and send it as a payload to queue

Choose your own queue technology. RabbitMQ is an obvious one, AWS SQS another. Make sure you deploy RabbitMQ on its own EC2 instance. You can find various installation instructions here. We have tested the Ubuntu install and it works fine.

Your aim is to keep response times as low as possible. One free tier server will probably get pretty busy, so you will want to introduce load balancing.

You can set up AWS Elastic Load Balancing using either Application or Network load balancers. Enable load balancing with e.g. 4 free tier EC2 instances and see what effect this has on your performance.

A tutorial here should help.

Step 2 - Implement a Consumer

Implement a plain old Java program to pull messages off the queue. This program simply receives messages from the queue and keeps a record of the individual lift rides for each skier in a hash map.

Your aim is to consume messages, ideally, as quickly as they are produced. This means your consumer will need to be multithreaded and your hash map thread safe.

Load Testing

Your aim here is to find the ‘best’ application configuration in terms of responsiveness to the client and managing queue size.

The questions you need to explore are:

• Do I need to scale out with load balancing for my server? Or can my system work with 1 free-tier server. Or a single, maybe small instance? Or ….?
• How many queue consumers threads do I need to keep the queue size as close to zero as possible?

You can use the RabbitMQ management console to track the number of messages in the queue, and producers and consumer rates.

Submission Requirements

Submit your work to Canvas Assignment 2 as a pdf document. The document should contain:

1. The URL for your git repo. Create a new folder for your Assignment 2 server code
2. A 1-2 page description of your server design. Include major classes, packages, relationships, how messages get sent/received, etc
3. Test runs (command lines, RMQ management windows showing queue size, send/receive rates) for 64, 128 and 256 client threads
4. Results for a test with 512 client threads

Grading:

1. Server and consumer implementations working (15 points)
2. Server design description (5 points) - clarity of description, good design practies used
3. Results (15 points) - throughput, different instances, basically describe and analyze what you did
4. Results of a successful run with 512 client threads (5 points)

Deadline: 3/11 11.59pm PST

Addendum: Multithreading and RabbitMQ

RabbitMQ and multithreading needs a few considerations. Read on ….

The basic abstraction that needs to be operated on by each thread is the channel. This means:

In your servlet (or equivalent if not using a servlet):

1. In the init() method, initialize the connection (this is the socket, so is slow)
2. In the dopost(), create a channel and use that to publish to RabbitMQ. Close it at end of the request.

This should work fine, although the documentation say channels are meant to be long-lived and caution again churn.

So a better solution would be to create a channel pool that shares a bunch of pre-created channels (in .init()) to form a connection pool.

Roll your own is not too hard, but apache commons has a generic pool implementation that you could build on. The reading has an example of how to do this.

Another approach to implementing a channel pool would be to use a BlockingQueue. Not too tricky … give it a try!

On the consumer side, you probably want a multi-threaded consumer that just gets a message and writes to the hash map. In this case you can just create a channel per thread and all should be fine.

There’s an excellent write up that describes the complexities of multi-threaded RMQ clients here

And here’s some sample code you can work from.

Back to Course Home Page