Support reading from systemd

Currently we rely solely on the node logging to a file. This script then reads that file and does its thing. However, that has a feew downsides.

I want to have blockperf be able to read from systemds journal. So that a node does not need to log to a file on the fs but use journald for that. That has some benefits:

The node operator can plug the node easier into his "log aggregation" setup
The logfile can not fill up the diskspace (... more or less)
For blockperf its simpler to read the stream from systemd then to do that "rotating logfile tail"...

Below: is a python implementation of the cli command journalctl -fu cardano-node

#!/usr/bin/env python3
import sys
from datetime import datetime

try:
    from systemd import journal
except ImportError:
    sys.stdout.write(
        "This script needs python3-systemd package.\n"
        "e.g.: https://github.com/systemd/python-systemd\n\n"
    )


def main():
    # Open a Reader to connect to journald
    jr = journal.Reader()
    # Specify a matcher, like -u in journalctl
    jr.add_match(_SYSTEMD_UNIT="cardano-node.service")
    # We want everything there is
    jr.log_level(journal.LOG_DEBUG)
    # move to the end
    jr.seek_realtime(datetime.now())
    while True:
        # wait blocks until there is some new event in the reader
        event = jr.wait()
        # Events can be of various kinds, we only want the ones that add stuff
        if event == journal.APPEND:
            # the reader is a generator of entries, give me all of them in a loop
            for entry in jr:
                # the entry has different fields (mostly journald specific)
                # MESSAGE is what was logged
                print(entry["MESSAGE"])

if __name__ == '__main__':
    main()

cardano-foundation / blockperf

Support reading from systemd #6