Ever need to do some math during policy evaluation? Sometimes configuration settings are based on available resources. For example, what if you want to calculate the size of shared buffers to be 25% of your available memory? Let’s write some policy. First, we need to figure out how much memory we have. Let’s parse this out from /proc/meminfo: So, we have 65505464 kB of memory in total. Knowing that we can use eval() to calculate what 25% is. eval() can also be used to test truthfulness.

Within the configuration management space, people often distinguish between agent-based and agent-less approaches. In short, an agent-based solution means that you install a software agent to run in the background / periodically on the system. That software agent then makes changes to the system as desired, and also commonly communicates over the network to send and receive updates, policy, commands, scripts, data, etc.

Ever need to visualize the data your working with? storejson() to the rescue! Let’s re-visit our example for sys.os_release from Feature Friday: Special variables: So, we saw the value of a single key, but if we don’t know what keys are available it can be useful to render the JSON representation. The with attribute in combination with storejson() provides a convenient way to visualize the JSON representation of structured data in CFEngine.

I promised more Build modules in my previous monthly Monday module blog post: package-method-winget. And here they are: windows-capability and windows-optional-feature.

Ever want a custom CFEngine Agent logo? Check out agentsvg. You can find agentsvg in core/contrib/ it’s a python script that can generate CFEngine agent logos. In addition to customizing the head and body colors you can customize the arm positions to be up, down, out or angled and the legs can be straight or out Happy Friday!

Did you know you can use variables in class expressions? If you are reading this, you probably are already familiar with the ability to use class expressions to restrict the context of multiple promises. For example, here we have three reports type promises, all guarded by the class expression linux::.

Class expressions are powerful. They let you restrict the context for multiple promises in a single statement. What if you want to further control the context of a specific promise? Let’s take a look at a contrived example: /tmp/feature-friday-28-0.cf command output Here, we have a report showing the distribution we’re running through class expressions protecting the individual promises. We would see I love Linux! on Linux hosts.

When promises are actuated, a class can be defined based on its result. For example, if a promise modifies a file’s content, you could define a class that indicates it has been repaired. However, did you know that promises can have multiple outcomes concurrently? That’s right! Native promises (but not custom promises) can have multiple outcomes. For example, a promise can be both kept and repaired at the same time. Let’s take a look.

There’s a users promise type for managing local users. However, did you know there is also a custom one for managing local groups? You might have seen it mentioned in the CFEngine Build announcement, the blog post on Managing local groups, or in the announcement supporting custom bodies post. But let’s take another look. The easiest way to integrate the groups custom promise type is by using cfbs, simply cfbs add promise-type-groups in your project.