Last year we had a look at managing local groups with the custom groups promise type. As you may or may not recall, we used JSON-strings to imitate CFEngine bodies. This was due to the fact that the promise module protocol did not support bodies at that time. Today, on the other hand, we’re happy to announce that as of CFEngine 3.20, this will no longer be the case. In this blog post we’ll introduce the long awaited feature; custom bodies. We’ll have a look at it from both the policy writers- and the promise module developers point of view.
Manually managing groups on a large infrastructure can be a tedious task, and is therefore best suited through automation software like CFEngine. Unfortunately - at time of writing - CFEngine does not have any built-in promise types for managing groups. But fear not; in CFEngine 3.17, custom promise types were introduced. This new exhilarating feature does not only allow for members of our community to make their own custom promise types, but also lets the CFEngine Core developers prototype new future promise types. In this blog post, I’d like to introduce one of our prototypes; the experimental groups promise type.
cf-remote is a tool for downloading and installing/deploying CFEngine. It automates a lot of the things you have to do before CFEngine is actually installed on your infrastructure, such as provisioning cloud instances, downloading CFEngine installers, copying them to remote hosts and installing / bootstrapping. To make it as easy as possible to get started with cf-remote and CFEngine, it is now available on pypi.
Getting started Installing cf-remote is as easy as:
CFEngine 3.17.0 introduced custom promise types, which enable CFEngine users to extend core functionality and policy language in a simple way. As an example of the power and simplicity of this new feature, I will show a promise type that helps to observe a website’s status. The module which implements this promise type was written in a couple of hours.
Creating a promise type for whether a site is up We will use Python and the CFEngine library to implement a promise module. Our previous blog post, “How to implement CFEngine custom promise types in Python”, explains this in detail.
This tutorial focuses on how to write a promise module, implementing a new CFEngine promise type. It assumes you already know how to install promise modules and use custom promise types, as shown in the previous blog post.
Why Python? Promise modules can be written in any programming language, but there are some advantages of using python:
Readable and beginner friendly language / syntax Popular and familiar to a lot of people, also used in some CFEngine package modules Big standard library, allowing you to reuse data structures, parsers, etc. without reinventing the wheel or adding dependencies Official CFEngine promise module library Most of the code needed is already done (protocol, parsing, etc.) You can focus on only the business logic, what is unique to your new promise type With that said, there are some reasons why you might not always want to use python:
Nightly packages are very useful for testing new features of CFEngine. Right now (as of August 2020), nightly packages can be used to test out these new features:
Compliance Reports. Mission Portal Dark Mode. New host info page with variable pinning and copy buttons. Note that these features are in development, some parts may be unfinished or buggy. Nightly packages are not supported and should not be used in production environments.
About a year ago, I wrote a small python script to automate installing and bootstrapping CFEngine on virtual machines in AWS. It had some hard coded IP addresses that I needed to update when I spawned new hosts, but other than that, it worked well. During manual testing, it saved me a lot of time instead of having to do things manually. Deploying CFEngine normally consists of these steps:
Determine what CFEngine package to use. Download appropriate package if you haven’t already - curl. Copy the package to the host - scp. Log into the host - ssh. Install the package - rpm / dpkg. Bootstrap CFEngine - cf-agent -B. At a company hackathon I decided to make my script into something better, something that would be useful to my colleagues, and maybe even CFEngine users in general. Enter cf-remote.
