Log impilict constraints to log if level=trace

[softwaremastermind]

Description

This merge request resulted from a troubleshooting process in an internal Nomad cluster. Before Nomad performs an evaluation, it adds a set of implicit constraints to a job (Job#admissionMutators).
The information about all implicit constraints considered in the log files would have supported troubleshooting. This merge request offers code that logs the implicit constraints when the log level is trace.

Testing & Reproduction steps

I have made some minor changes to the Vagrant setup to run Vagrant on Ubuntu 24.04.2 LTS.

Links

Scheduling in Nomad

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[tgross]

Hi @softwaremastermind! The job inspect command already includes all this information because its persisted to Raft. I'm having trouble imagining a debugging scenario where it'd be more useful to have this in logs (typically available only to the cluster admin) vs the job inspect (available to any job author).

Do you typically run with trace logging enabled? I worry this could get really expensive for busy clusters when running tools like nomad operator debug.

[softwaremastermind]

Hi @tgross, thank you very much for the fast and appreciative reply.

We do not run with log level trace in production.
I will look into job inspect output and will try to replicate the err.

[tgross]

@softwaremastermind the other tool that might help you if you want more continuous monitoring is the event stream API. That reflects the writes that Nomad makes to its internal state store, so that'd include any implicitly created constraints as well. You can subscribe to subsets of the stream by topic or namespace.