Cdist

Development

cdist development started in 2010 at ETH Zurich and is actively being developed by a lot of free and open-source software contributors and maintained by the two main developers Nico Schottelius and Steven Armstrong. The major part of the discussion about cdist happens on the mailinglist and on the IRC channel #cstar in the Freenode network. cdist is being used at various companies in Switzerland (for instance at ETH Zurich and The OMA Browser project), the US, Germany and France.

Features

cdist is a zero dependency configuration management system: It requires only ssh and a bourne-compatible shell on the target host, which is usually enabled on all Unix-like machines. Because of this, cdist can be used to bootstrap other configuration management systems.

Installation and configuration

cdist is not installed traditionally as a package (like .deb or .rpm), but installed via git. All commands are run from the created checkout. The entry point for any configuration is the shell script conf/manifest/init, which is called initial manifest in cdist terms.

The main components of cdist are so called types, which bundle functionality. The types essentially consists of a number of shell scripts to define which types a type reuses and which code is generated to be executed on the target host.

Architecture

cdist is split into two components:

The core

The configuration

Core

The core of cdist is implemented in Python 3 and provides the executables to configure target hosts. The core operates in a push model: It connects from the source host to the target hosts and configures the machines. For communication and file transfer SSH is being used. To allow parallel configuration of hosts, the core supports a parallel mode in which it creates a child process for every connection. This model allows cdist to scale horizontally with the available computing resources: If at a certain limit is reached and the capacity of the available CPUs has been used, adding another CPU or distributing cdist to multiple hosts allows to configure more hosts in parallel.

Configuration

The configuration is written in Bourne Shell and consists of

The initial manifest (which defines which host is assigned which types)

Global Explorers (to gain information about the target system)

Types (which provide all functionality and consist of a manifest, type explorers and gencode scripts)

Although all of these are written in Shell script, the order of execution in the manifests does not matter: cdist employs an idempotent configuration.

Comparison

In comparison to most other configuration management software, cdist does not have any requirements on the target host besides SSH and a bourne shell. It requires Python 3.2 on the source host, though. cdist operates in push based approach, in which a server pushes configurations to the client and the clients do not poll for updates.

Configuration language

All user configurable parts are contained in manifests or gencode-scripts, which are shell scripts. Shell scripts were chosen, because Unix System Administrators are usually proficient in reading and writing shell scripts. Furthermore, shell is also commonly available on potential target systems, thus avoiding the need to install additional software there ("zero dependencies").

cdist reads its configuration from the initial manifest (conf/manifest/init), in which hosts are mapped to types:

When using the types in cdist, they are called like normal programs in manifests and can make use of advanced parameter parsing as well as reading from stdin:

Dependencies are expressed by setting up the require environment variable:

__directory /tmp/foobar require="__directory//tmp/foobar" __file /tmp/foobar/baz

Access to paths and files within types is given by environment variables like $__object.