I do not like how Fedora CoreOS configures `sudo` to allow the *core*
user to run privileged processes without authentication. Rather than
assign the user a password, which would then have to be stored
somewhere, we'll install *pam_ssh_agent_auth* and configure `sudo` to
use it for authentication. This way, only users with the private key
corresponding to one of the configured public keys can run `sudo`.
Naturally, *pam_ssh_agent_auth* has to be installed on the host system.
We achieve this by executing `rpm-ostree` via `nsenter` to escape the
container. Once it is installed, we configure the PAM stack for
`sudo` to use it and populate the authorized keys database. We also
need to configure `sudo` to keep the `SSH_AUTH_SOCK` environment
variable, so *pam_ssh_agent_auth* knows where to look for the private
keys. Finally, we disable the default NOPASSWD rule for `sudo`, if
and only if the new configuration was installed.
`upsmon` is the component of NUT that tracks the status of UPSs and
reacts to their changing by sending notifications and/or shutting down
the system. It is a networked application that can run on any system;
it can run on a different system than `upsd`, and indeed can run on
multiple systems simultaneously.
Each system that runs `upsmon` will need a username and password for
each UPS it will monitor. Using the CUE [function pattern][0], I've
made it pretty simple to declare the necessary values under
`nut.monitor`.
[0]: https://cuetorials.com/patterns/functions/
I keep going back-and-forth on whether or not collectd should run in a
container on Fedora CoreOS machines. On the one hand, running it
directly on the host allows it to monitor filesystem usage by mount
point, which is consistent with how non-FCOS machines are monitored.
On the other hand, installing packages on FCOS with `rpm-ostree` is a
nightmare. It's _incredibly_ slow. There's also occasionally issues
installing packages if the base layer has not been updated in a while
and the new packages require an existing package to be updated.
For the NUT server specifically, I have changed my mind again: the
*collectd-nut* package depends on *nut-client*, which in turn depends on
Python. I definitely want to avoid installing Python on the host, but I
do not want to lose the ability to monitor the UPSs via collectd. Using
a container, I can strip out the unnecessary bits of *nut-client* and
avoid installing Python at all. I think that's worth having to monitor
filesystem usage by device instead of by mount point.
A bunch of stuff that wasn't schema definitions ended up in the `schema`
package. Rather than split values up in a bunch of top-level packages,
I think it would be better to have a package-per-app model.
Although KCL is unquestionably a more powerful language, and maps more
closely to my mental model of how host/environment/application
configuration is defined, the fact that it doesn't work on ARM (issue
982]) makes it a non-starter. It's also quite slow (owing to how it
compiles a program to evaluate the code) and cumbersome to distribute.
Fortunately, `tmpl` doesn't care how the values it uses were computed,
so we freely change configuration languages, so long as whatever we use
generates JSON/YAML.
CUE is probably a lot more popular than KCL, and is quite a bit simpler.
It's more restrictive (values cannot be overridden once defined), but
still expressive enough for what I am trying to do (so far).
Dustin