Caerbannog

Caerbannog makes it easy to write declarative Python scripts to automatically configure your local user accounts.

Example

Create a configuration script

First, create a configuration script to describe the various types of devices on which you want to configure your user account:

./configure.py:

from caerbannog.prelude import *

target("laptop").depends_on("windows")
target("desktop").depends_on("archlinux")
target("work-laptop").depends_on("windows").has_roles("vscode")

target("windows").depends_on("common").has_roles("powershell", "windows-terminal")
target("archlinux").depends_on("common").has_roles("zsh", "bspwm", "vim")

target("common").has_roles("git")

commit()

Create role files

Now create roles which describe applications or configurations that you want to deploy. For instance, for git, you may want to install the package and create a .gitconfig and global .gitignore in your home directory:

roles/git/role.py:

from caerbannog.roles.prelude import *

def configure():
    Do(
        Package("git").is_installed(),
        File(home_dir(".gitconfig")).has_template("gitconfig.j2"),
        File(home_dir(".gitignore")).has_lines(".vscode"),
    )

roles/git/gitconfig.j2:

[core]
	hooksPath = "~/.githooks"
[user]
	name = Edsger Dijkstra
	email = dijkstra@novigrad.rd
[fetch]
	prune = true
[pull]
	rebase = true

Run it!

Now run the script to bring your machine to its desired state:

$ python configure.py apply laptop

All actions that are taken and changes that are made are clearly reported:

How does it work?

Caerbannog allows you to write code that specifies what your system should look like. For instance, you can declare that the file .gitignore in your home directory has .vscode as its content in the following manner:

File(home_dir(".gitignore")).has_lines(".vscode")

If the file exists in your home directory, and it has the content you specified, no action will be taken. If it is not present, it will be created. If it exists, but its content differs, it will be modified.

To keep related assertions together, you can group them by creating roles, and placing all related assertions within those roles. In this case, it makes sense to create a git role which also asserts that your .gitignore has the right content, and that the git package is installed.

Often, you will want to configure multiple devices, and not always all in the same way. To allow for this, you can create targets. By assigning roles to targets, you can selectively apply roles to different devices.

These targets are specified in the configure.py script.

target("laptop").has_roles("git")

Now, if you run the script, you can apply the git role by selecting the laptop target:

python ./configure.py apply laptop