Turn APC UPS status `apcaccess status` to OpenMetrics (prometheus) exporter with zero-dependency Python script & systemd socket.

apcmetrics.py

#!/usr/bin/env python3
import sys
import socket
from subprocess import Popen, PIPE


def main():
    sock = socket.fromfd(3, socket.AF_INET, socket.SOCK_STREAM)

    while True:
        conn, addr = sock.accept()
        print("Connection from", addr)
        try:
            handle_client(conn)
        except Exception as e:
            print(e, file=sys.stderr)


def handle_client(sock):
    proc = Popen(
        ['/usr/bin/apcaccess', 'status'],
        stdout=PIPE,
        text=True,
        env=dict(),
    )
    outs, _ = proc.communicate(timeout=5)
    kvs = (l.split(':', 1) for l in outs.split('\n') if ':' in l)
    kvs = { k.strip(): v.strip() for k, v in kvs }

    f = sock.makefile('rw', encoding='utf-8')
    f.write("HTTP/1.0 200 OK\r\n")
    f.write("Server: apcmetrics\r\n")
    f.write("Content-Type: application/openmetrics-text; version=1.0.0; charset=utf-8\r\n\r\n")

    def parse_float(value):
        if ' ' in value:
            value, _unit = value.split(' ', 1)
        return float(value)

    def parse_int(value):
        return int(parse_float(value))

    def metric(name, value_fn, typ, help, unit=None):
        value = value_fn(kvs[name])
        path = f"apcmetrics_{name.lower()}"
        if unit is not None:
            path += f"_{unit}"
        f.write(f"# HELP {path} {help}\n")
        f.write(f"# TYPE {path} {typ}\n")
        if unit is not None:
            f.write(f"# UNIT {path} {unit}\n")
        f.write(f"{path}{{host=\"{kvs['HOSTNAME']}\"}} {value}\n")

    metric('LINEV', parse_float, 'gauge',
            'Current input line voltage', 'volt')
    metric('LOADPCT', parse_float, 'gauge',
            'Percentage of UPS load capacity used as estimated by UPS', 'precent')
    metric('BCHARGE', parse_float, 'gauge',
            'Current battery capacity charge percentage', 'precent')
    metric('TIMELEFT', parse_float, 'gauge',
            'Remaining runtime left on battery as estimated by the UPS', 'minutes')
    metric('BATTV', parse_float, 'gauge',
            'Current battery voltage', 'volts')
    metric('NUMXFERS', parse_int, 'gauge',
            'Number of transfers to battery since apcupsd startup')
    metric('TONBATT', parse_int, 'gauge',
            'Seconds currently on battery', 'seconds')
    metric('CUMONBATT', parse_int, 'gauge',
            'Cumulative seconds on battery since apcupsd startup', 'seconds')

    f.write("# EOF")

    f.flush()
    sock.shutdown(socket.SHUT_RDWR)
    sock.close()

if __name__ == '__main__':
    main()

apcmetrics.service

[Unit]
Description=APC USP OpenMetrics explorer

[Service]
Type=simple
DynamicUser=yes
WorkingDirectory=/opt/apcmetrics
ExecStart=/usr/bin/python apcmetrics.py

Environment=PYTHONUNBUFFERED=1

PrivateTmp=true
PrivateDevices=true
ProtectSystem=strict
ProtectHome=true
ProtectKernelModules=true
ProtectControlGroups=true
ProtectKernelTunables=true
ProtectProc=invisible
ProtectHostname=true
RestrictNamespaces=true
SystemCallArchitectures=native
ProtectClock=true
ProtectKernelLogs=true
MemoryDenyWriteExecute=true
PrivateUsers=true
RestrictAddressFamilies=AF_INET
RestrictRealtime=true
LockPersonality=true
SystemCallFilter=@system-service @basic-io @network-io @io-event @aio @file-system
SystemCallFilter=~@resources @privileged
CapabilityBoundingSet=

apcmetrics.socket

[Unit]
Description=Listen on http for APC UPS metrics.

[Socket]
ListenStream=127.0.0.80:3060
Accept=no

[Install]
WantedBy=sockets.target