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cthulhu

A container-based distributed system testing framework that is portable and easy to use locally.

The cthulhu test framework is a distributed testing framework that should be used for correctness testing, not performance testing, as the underlying bin packing, deployment, and monitoring system offered by this framework uses Docker under the hood.

Nearly all distributed system testing frameworks do too much and don't expose the hooks you need to test your distributed system. Often, the testing framework itself requires that you write in a particular language, using a particular sytax, using a custom framework. What's more, if you're application isn't written in a way that lends itself to inspection, you're mostly out of luck. The cthulhu distributed system testing frameworks seeks to keep it simple by exposing your distributed system as a filesystem.

getting started

You will need to install virtualenv if it isn't already installed. You may need to use your native package manager to install this if pip isn't available on your system. For example, on Ubuntu you'll need to run apt-get install python-virtualenv.

Create and activate a virtual environment for the cthulhu project using virtualenv.

cd cthulhu
python setup.py virtualenv
source activate
python setup.py develop

Next, you'll need to make sure that docker (eek!) is available on your platform and runnable by a non-root user. Follow docker's instructions online to download install and configure docker on your platform.

Now you can run cthulhu.

cthulhu -h

fixtures

Use cthulhu to create distributed test fixtures.

cthulhu --instances 3 --docker-image hello-world

You'll see that the framework creates a fixture on disk for you that you can leverage in your correctness tests using a system such as bats.

cthulhu-fixture/
├── 172.17.0.2
│   ├── bindmounts
│   │   ├── etc
│   │   │   └── config.json
│   │   └── var
│   │       └── i001.log
│   ├── control
│   └── pid.txt
├── 172.17.0.3
│   ├── bindmounts
│   │   ├── etc
│   │   │   └── config.json
│   │   └── var
│   │       └── i002.log
│   ├── control
│   └── pid.txt
├── 172.17.0.4
│   ├── bindmounts
│   │   ├── etc
│   │   │   └── config.json
│   │   └── var
│   │       └── i003.log
│   ├── control
│   └── pid.txt
├── control
├── i001 -> /home/ubuntu/workspace/gallocy/cthulhu-fixture/172.17.0.2
├── i002 -> /home/ubuntu/workspace/gallocy/cthulhu-fixture/172.17.0.3
└── i003 -> /home/ubuntu/workspace/gallocy/cthulhu-fixture/172.17.0.4

A few key take aways from this output are:

  1. Each node in the topology is assigned its own IP address that is represented as a directory.
  2. Each node in the topology is assigned a short name, e.g., i001, i002, i003, which corresponds to an IP address. These short names can also be used with the docker command line.
  3. Each node in the topology automatically has two bindmounts created: etc and var. These can be used to pass configuration or retrieve logs from the node.
  4. Each node has a control script that takes a start or stop command to start or stop the container, respectively.
  5. The topmost control script starts or stops all of the containers.

See the sample directory for additional exploration of the above example.

about

I started cthulhu to test gallocy, a distributed shared memory system. Other distributed system testing frameworks suffered from the problems I mentioned above, so I caved in and wrote my own.

I know the documentation sucks. If you're interested in learning more about this tool, please open an issue so I know you're curious, and I'll happily update the document further.