cdist - the setup

Configuration management

Cdist is a little piece of software which makes setting up new servers a little less painful. I believe the main advantage of using software like this is not the easy setup but the fact that the process creates executable documentation. Cdist is new when compared to Puppet, Chef and a couple of others. It appealed to me because it’s not much more that a glorified bunch of shell scripts. The other approaches I saw required a central server, pushing code around and not the mention the requirement that Ruby should already be installed on the target system.

Getting started

This couldn’t be easier, just clone the repo. You’ll need Python3, I suggest using Homebrew instead of Mac Ports. It took me a bit more time to understand that all my code should go in this cloned repo. Just start typing away. The maintainer suggests pushing to a different remote and to work on your own branch. This way a git pull will bring you up to date. A valid strategy I suppose but uncommon.

But then…

I followed the quickstart example but as you notice it’s a link to the git repo as this is not yet officially released. Following along is pretty easy until I hit

$ echo '__file /etc/cdist-configured' > conf/manifest/init

What does that do?

Types

The __file denotes a ‘type’, the file immediately behind it is the argument you might pass. These two combined form an object which can be reference later. I’ll get back to that (under Dependencies).

Manifest

The conf/manifest/init is the most important file. As far as I understood this file contains a long case statement enumerating all your servers. I’m just hoping you can use regular expressions or groups, all the nodes in our Riak cluster have the same setup and I’d hate it to list them all.

So

$ echo '__file /etc/cdist-configured' > conf/manifest/init

will make a manifest which does little. The __file type will create a file if it is not there already.

Do it already!

Assuming you can login with your SSH key as root:

$ cdist config your-remote-server

I was momentarily confused by the config switch as there also is an install switch which function I have yet to determine. The above command will go to your server and configures (or installs?) it.

Dependencies

More often than not you want to execute some piece of code if a condition is fulfilled. Cdist has a special feature to declare dependancies. You can assign a value to the variable require immediately follow but the code to be executed when the condition holds:

require="__file/etc/cdist-configured" __link /tmp/cdist-testfile --source /etc/cdist-configured  --type symbolic

This seems weird and I think it is. The advantage of doing it like this is that you can use the magic objects created when you call a type.

EC2

As a small side note; Cdist’s OS detection does not work on Amazon’s standard AMI’s. This bit me when wanting a quick, clean server to try this out on.