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Piazza Strawman

This is an exploration of some of the technical ideas that will go into the Piazza project. The key concept is messaging queues as a technique for decoupling ingestion of data from processing. We provide implementations of some web services and data processing facilities based around this idea, and scripts to deploy them on a virtual network.

Setup

We use a number of third-party components for this project which are insuitable for inclusion in the git repository, but a script is provided to help download them. The script will also compile the code under the services/ directory and make it available for the virtual machine deployment scripts. To run the setup script and the virtual network, you will need:

This script is tested on Mac OSX but should work on Linux as well with these tools installed. To run, change directories to the root of the checked-out project and type sh setup.sh.

This will download a lot of data and likely take a while the first time it runs, subsequent runs should be faster.

After setup.sh is done, you can instantiate the virtual network by changing directories to the messaging directory and running vagrant up. Vagrant may need to download a virtual machine image so again this may take a while. Also you'll need about 4GB of free space for the virtual machines to run.

Once Vagrant finishes, you should be able to visit http://192.168.23.11:8080/ in your web browser and see a simple web page that exercises the data processing pipeline.

Vagrant notes

The following are some common useful commands for working with the vagrant-managed machines. Most commands accept a machine name (geoserver, database, or messaging) to target only a single machine from the virtual network. If the name is omitted, some commands will apply to all machines and others will fail.

  • vagrant up creates a machine if it doesn't already exist, or starts it if it exists but it stopped.

  • vagrant ssh opens an SSH shell session with the specified machine. This uses the vagrant user which has permission to sudo without a password.

  • vagrant rsync copies files from the messaging/ directory to the vagrant user's ~/sync/ directory on the virtual machine.

  • vagrant destroy completely erases the virtual machine.

  • vagrant halt shuts down the virtual machine but preserves its virtual hard drive.

  • vagrant provision re-runs the setup scripts without erasing anything. The ansible scripts we use are intended to support this type of usage.