Controling a group of daemons and timer jobs with a systemd target

README.md

Controling a group of daemons and timer jobs with a systemd target

Scenario

The custom web application My App, in addition to its web server request-driven work, has three daemons (able, baker and charlie) and three jobs (dog, easy and fox) that run (cron-like) on a pre-defined schedule.

Requirements

The app needs these all to be in one of two states

State	description
Up	all the daemons are running and the jobs run according to their respective schedules
Down	all daemons are stopped and the jobs do not run

We want to use systemd to

• enforce this Up/Down policy,
• give the operator (and scripts etc.) a means to switch between Up and Down states, and
• start the daemons and jobs at an appropriate stage of system startup (in this case that is not before the local MariaDB database service is up).

Design

• Install a custom systemd target unit myapp_master.target on which to use systemctl commands
• Use one service unit to mange each of the daemons
• For each job, use a systemd timer unit, each with a corresponding service unit to run the job
• Make the daemon service and timer units depend on the master target

See the unit files for details.

myapp_able.service

# myapp_able.service
[Unit]
Description=My App Able daemon
After=myapp_master.target
BindsTo=myapp_master.target

[Service]
ExecStart=/usr/local/bin/myapp_daemon Able
Restart=always

[Install]
WantedBy=myapp_master.target

myapp_baker.service

# myapp_baker.service
[Unit]
Description=My App Baker daemon
After=myapp_master.target
BindsTo=myapp_master.target

[Service]
ExecStart=/usr/local/bin/myapp_daemon Baker
Restart=always

[Install]
WantedBy=myapp_master.target

myapp_charlie.service

# myapp_charlie.service
[Unit]
Description=My App Charlie daemon
After=myapp_master.target
BindsTo=myapp_master.target

[Service]
ExecStart=/usr/local/bin/myapp_daemon Charlie
Restart=always

[Install]
WantedBy=myapp_master.target

myapp_daemon

#!/usr/bin/env php
<?php

array_shift($argv);
$name = 'My App: ' . (implode(' ', $argv) ?: bin2hex(random_bytes(4))) . ' (' . posix_getpid() . ')';
$signals = [
    SIGTERM => 'TERM',
    SIGINT => 'INT',
    SIGHUP => 'HUP',
    SIGUSR1 => 'USR1',
    SIGUSR2 => 'USR2',
];

function signalHandler(int $signalNumber)
{
    global $name, $signals;
    echo "$name received {$signals[$signalNumber]} signal.";

    if (in_array($signalNumber, [SIGTERM, SIGINT])) {
        echo " Exiting\n";
        exit;
    }

    echo "\n";
}

foreach ($signals as $signal => $ignore) {
    pcntl_signal($signal, "signalHandler");
}

echo "$name started.\n";
while (true) {
    usleep(100000);
    pcntl_signal_dispatch();
}

myapp_dog.service

# myap_dog.service
[Unit]
Description=My App Dog job

[Service]
Type=oneshot
ExecStart=/bin/echo My App job Dog ran!

myapp_dog.timer

# myapp_dog.timer
[Unit]
Description=My App Dog timer job
Requires=myapp_master.target

[Timer]
OnCalendar=*:*:00
Persistent=true

[Install]
WantedBy=myapp_master.target

myapp_easy.service

# myap_easy.service
[Unit]
Description=My App Easy job

[Service]
Type=oneshot
ExecStart=/bin/echo My App job Easy ran!

myapp_easy.timer

# myapp_easy.timer
[Unit]
Description=My App Easy timer job
Requires=myapp_master.target

[Timer]
OnCalendar=*:*:20
Persistent=true

[Install]
WantedBy=myapp_master.target

myapp_fox.service

# myap_fox.service
[Unit]
Description=My App Fox job

[Service]
Type=oneshot
ExecStart=/bin/echo My App job Fox ran!

myapp_fox.timer

# myapp_fox.timer
[Unit]
Description=My App Fox timer job
Requires=myapp_master.target

[Timer]
OnCalendar=*:*:40
Persistent=true

[Install]
WantedBy=myapp_master.target

myapp_master.target

# test_master.target
[Unit]
Description=My App daemon and job master
After=mariadb.service

[Install]
WantedBy=multi-user.target