Daemon Module

A daemon is a process which is running in the background which does work for your application.

Why would you need a daemon for your application?

• Run a reporting engine in the background
• Poll a database table for pending tasks
• Reading and importing log files
• Converting or processing images

Zesk daemons allow you to run individual methods in your Zesk application as daemons to do work. It has features such as:

• Automatic detection of daemon methods in all loaded modules
• Automatic management of daemon processes, with ability to stop and start individual methods
• Reporting of daemon status via cron task
• Ability to have multiple processes for each method
• Hook invocation on fork on master and child processes

Create your first daemon

TODO

Running your daemon

TODO

Controlling the number of daemon processes per method

TODO

How the Daemon command works

TODO

Daemon care and best practices

1. Daemon processes should auto-restart

With any scripting language and background process, memory issues and long-term process garbage collection may accumulate over time. If your daemon processes die, they should be restarted.

We recommend D.J. Bernstein's daemontools which is packaged with many server distributions. Naturally, your daemon processes should use setuidgid to your web user prior to running.

A sample daemontools run script looks like this:

#!/bin/bash
failed() {
    echo "$*" 1>&2
    sleep 10
    exit 1
}
conf=/etc/aweseome.conf
env_files="$conf $(dirname $(pwd))/.env $(pwd)/.env"
for f in $env_files; do
    if [ ! -f $f ]; then
        echo "$f does not exist"
    else 
        source $f
    fi
done
if [ -z "$APP_ROOT" ]; then
    failed "APP_ROOT not defined in $env_files"
fi
if [ -z "$ZESK" ]; then
    ZESK=$APP_ROOT/vendor/bin/zesk
fi
if [ ! -x "$ZESK" ]; then
    failed "ZESK binary not installed at $ZESK"
fi
if [ -z "$APP_USER" ]; then
    failed "APP_USER not defined in $env_files"
fi
echo Starting in $APP_ROOT
if ! cd $APP_ROOT; then
    failed "Can not cd to $APP_ROOT - permissions problem"
fi
exec setuidgid $APP_USER $ZESK daemon --watch $APP_ROOT

You can configure your application by creating awesome.conf and /etc/service/awesome/.env

2. Have your daemon monitor the codebase, links, and any other related media

We recommend running your daemons using something which auto-restarts them when the processes quits; why? It simplifies deployments and development, generally.

That said