Helper library of common operations

[stub42]

There are many common operations that charms need to perform on the deployed machine to setup and maintain the deployed software. Many of these have accumulated in the charm-helpers library. It would be good if a coherent version of these helpers was either provided as part of the operator framework, or in a blessed module charmers are encouraged to include.

Operations such as:

• create a directory securely, setting ownership and permissions
• write a file securely, setting ownership and permissions
• systemd service control (start, stop, enable, disable, status)
• render a template (per #228)
• create an OS user
• create an OS group
• add an OS user to an OS group
• generate a secure password
• generate a hash of a file (for detecting changes)
• change ownership and/or permissions, recursively
• get the amount of system RAM
• manage OS resource limits (generally to bump them up)
• detect if the host machine is a container (eg. ntpd should not be run in a container)
• install a certificate as a trusted certificate authority (/usr/local/share/ca-certificates/...)

(the above list from skimming charmhelpers/core/host.py)

Also functionality to install apt and snap packages, per apt and snap charms.reactive layers.

[jameinel]

I understand that these methods are there, I'm more curious to know how many charms are actually using them. There are things like https://pypi.org/project/psutil/ as well that we should look at.

[facundobatista]

We will address this list and take a decision in each case of how the functionality will be handled.

[jnsgruk]

This is now being worked on as a series of tightly scoped charm libraries by @rbarry82.

[benhoyt]

@jnsgruk It seems to me libraries are the way to do this, agreed? Either small charm-lib libraries or larger PyPI libs (or even 3rd party libraries like John M mentioned like psutil). Do you have a link to where @rbarry82's libraries ended up?

[jnsgruk]

They ended up in a charm named operator-libs-linux - we've actually added a docs page that tracks these libraries: https://juju.is/docs/sdk/library-index#heading--libraries-that-provide-tools-for-machine-charms

I think for now this is safe to close - the Operator Framework itself isn't the place for these things, and charm libs can be used to satisfy the same need.