psconfig stats pscheduler should print better error message when pscheduler not present

[szymontrocha]

In a central MA host when one issues a psconfig stats pscheduler command it fails with an ugly message:

$ psconfig stats pscheduler
Traceback (most recent call last):
  File "/usr/lib/perfsonar/psconfig/bin/commands/stats", line 50, in <module>
    metrics = calculator.run_metrics()
              ^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3/dist-packages/psconfig/utilities/metrics.py", line 121, in run_metrics
    with FileReadBackwards(self.agent_log_file(), encoding="utf-8") as frb:
         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3/dist-packages/file_read_backwards/file_read_backwards.py", line 41, in __init__
    self.iterator = FileReadBackwardsIterator(io.open(self.path, mode="rb"), self.encoding, self.chunk_size)
                                              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
FileNotFoundError: [Errno 2] No such file or directory: '/var/log/perfsonar/psconfig-pscheduler-agent.log'
$

it would be much better if it fails silently or prints some informative message like "This is an archive host. pscheduler is not present" or anything else then a code error

[laeti-tia]

And I guess in a testpoint-only host, we have the same when issuing a psconfig stats grafana, isn't it?

[valtersg]

Technically yes.
The stats command doesn't check if an agent is installed.
The 3 possible agents are hardcoded and the stats command just parses the corresponding log file either in /var/log/perfsonar/ or a directory provided by --logdir

[laeti-tia]

It should be good, but to be tested once the package lands in the snapshot repo.