A rough script for mux'ing the main cloud-init log and systemd's journal output

mux-logs.py

#!/usr/bin/python3

import io
import re
import datetime as dt
from subprocess import run, PIPE
from itertools import chain

def cloud_init_log():
    with io.open('/var/log/cloud-init.log', 'r', encoding='utf-8') as log:
        ts = None
        for line in log:
            try:
                new_ts = dt.datetime.strptime(line[:23], '%Y-%m-%d %H:%M:%S,%f')
                new_ts = new_ts.replace(tzinfo=dt.timezone.utc)
            except ValueError as e:
                message += '\n' + line
            else:
                if ts is not None:
                    yield ts, 'ci', message
                ts = new_ts
                message = line[26:].rstrip()
        yield ts, 'ci', message

def journal():
    out = run(['journalctl', '-o', 'short-iso-precise'], check=True, stdout=PIPE,
            stderr=PIPE, encoding='utf-8')
    ts = None
    for line in out.stdout.splitlines()[1:]:
        try:
            new_ts = dt.datetime.strptime(line[:31], '%Y-%m-%dT%H:%M:%S.%f%z')
        except ValueError:
            message += '\n' + line
        else:
            if ts is not None:
                yield ts, 'sysd', message
            ts = new_ts
            message = line[32:].rstrip()
    yield ts, 'sysd', message

for ts, source, msg in sorted(chain(journal(), cloud_init_log())):
    print('{ts:%Y-%m-%d %H:%M:%S.%f} {source:4s} {msg}'.format(
        ts=ts, source=source, msg=msg))