Basho Banjo is an experiment in using Riak Core to create a distributed orchestra powered by midi files. It serves as a simple example of how to create a distributed application with Riak Core.
To understand 'Banjo, you first need to understand a little about Riak Core. Riak Core is an open-source Erlang library that allows you to create masterless distributed applications using the principles described in Amazon's Dynamo Paper. For more information about Riak Core, you can view this presentation.
For our purposes, there are two main things to consider when creating an application on Riak Core:
Commands are the operations that you send to the system, and consist of an ObjectName and a Payload. Banjo commands consist of a command to play a note of a certain frequency/volume/duration.
The VNode Module is a pluggable module that conforms to an interface provided by Riak Core that accepts incoming commands and acts on them. The Banjo VNode accepts the incoming command to play a note, generates a wave file (if it doesn't already exist) and then plays the file using aplay or afplay, depending on the platform. (Mac and Linux are supported... Windows is not.)
With these two things implemented, Riak Core does the rest of the work. It uses a consistent hash to route notes to specific VNodes, and it takes care of assigning VNodes (a.k.a. Virtual Nodes) to physical nodes, and re-assigning the VNodes when you add/remove physical nodes to/from the cluster.
The last part of the equation is some code that uses an Erlang midi library developed by Jim Menard to parse midi files and extract notes. The code than iterates through the notes with the correct timing, generating play commands to send to Riak Core.
git clone firstname.lastname@example.org:rustyio/BashoBanjo.git cd BashoBanjo rebar deps get make rel
cd rel/basho_banjo bin/banjo console
If you want to run multiple nodes on a single computer, you can:
- Copy the files in
rel/basho_banjoto another directory.
etc/vm.argsand change the node name to something like
etc/app.configand change the handoff port to avoid a port conflict.
- Start the new node.
- Join the new node to the existing node from the Erlang console:
- Then, play a midi tune, which should play across both nodes: