Synopsis:

daemonizer is an application lifecycle management framework. It starts/stops applications and displays information about them. A typical use case is when you have a program that you would like to run as a UNIX daemon while being able to check its logs and stop when needed (a web server is a good example).

Without daemonizer doing this is a laborious task. You will have to do the following manually:

1. Start the application and send it to the background
2. Redirect its output to file and remember its location
3. Find the application's PID by looking through the list of processes
4. Make sure the app is not run multiple times
5. Invent the procedure and a shell script to gracefully stop the app
6. Invent the procedure to kill the app when it doesn't respond to a graceful shutdown request

...and lots of other things that daemonizer takes care of!

Prerequisites

1. Linux (will probably work under other UNIX-like systems, but this was never tested)
2. Perl 5
3. ps if you want to run tests or the example sleeper startup script

Installation:

1. Clone the repository into any directory your have write access for
2. Change the PATH variable in ~/.bashrc (assuming you cloned daemonizer to /home/${username}/opt/daemonizer"):

$ export PATH=/home/${username}/opt/daemonizer:$PATH

3. Re-read your Bash profile:

$ source ~/.bashrc

4. Make sure the program can be found: $ daemonizer core help

Component's responsibility:

daemonizer consists of several components each having its own scope and responsibility.

1. daemonizer - master script, defines environment variables, starts the runner
2. runner - manages basic application lifecycle (starts/stops/checks liveness), calls a startup script via deamonizer if the "start" command is specified and forwards unrecognized commands to the startup script
3. daemonize - makes an app a deamon if needed detaching from a controlling terminal. Terminates an application if someone deletes its PID. Can be used outside of the daemonizer framework as a standalone application
4. startup script - executes a command passed to it or executes an application if no command is provided
5. post-start script (optional) - runs a sequence of actions required for the program to become fully initialized (e.g. by adding entries to the database).

The call chain usually looks like this:

daemonizer --> runner --> daemonize --> startup script --> your application

Core startup script

There's a special startup script called "core" which serves a special purpose showing information about the framework (for example, the list of startup scripts).

Important: currently daemonizer is capable of handling only a single instance of each application (you need to create a separate startup script for each of them).

Examples:

Note: there is a sample script called "sleeper" that can be used to verify the functionality. It just sleeps for 60 seconds and then exits.

$ daemonizer sleeper start
$ daemonizer sleeper show     # Shows a PID and a log file location
$ daemonizer sleeper showlog  # Prints a log file content
$ daemonizer sleeper stop

In addition, your startup script might want to send, for example, SIGHUP to the controlled application in order to force it to reload the changed configuration. Or it might want to check the service's health by callingone of its endpoints. This is possible with daemonizer. To make sure the startup script supports custom commands, run the following (for the "sleeper"):

$ daemonizer sleeper listcommands # Prints a list of the application-specific commands

Then you can use such a command:

$ daemonizer stc-ws check    # Check the REST API health by calling one of its endpoints
$ daemonizer stc-ws showmem  # Show memory utilization

You might want to see all startup scripts:

$ daemonizer core showscripts # Prints a list of startup scripts