Hello World Example

This example demonstrates the basic functionality of systemg by running a simple shell script that prints incrementing line numbers.

Overview

The Hello World example shows you how to:

• Define a basic service
• Configure environment variables
• Set up restart policies for fault tolerance

Files

The example consists of two files:

Shell Script (hello-world.sh)

A simple script that prints incrementing numbers every 2 seconds:

#!/bin/sh

i=1

while true; do
    echo "Line number: $i"
    i=$((i + 1))
    sleep 2
done

Configuration (hello-world.sysg.yaml)

The systemg configuration file that defines how to run the service:

version: "1"
services:
  sh__hello_world:
    command: "sh hello-world.sh"
    env:
      file: ".env"
      vars:
        FOO: "foo"
    restart_policy: "on_failure"
    retries: "5"
    backoff: "5s"

Configuration Breakdown

Let's examine each part of the configuration:

Service Name

services:
  sh__hello_world:

The service is named sh__hello_world. Service names should be descriptive and unique within your configuration.

Command

command: "sh hello-world.sh"

This directive tells systemg which command to execute. In this case, it runs our shell script using the sh interpreter.

Environment Variables

env:
  file: ".env"
  vars:
    FOO: "foo"

Environment variables can be configured in two ways:

• file: Load environment variables from a .env file
• vars: Define inline environment variables directly in the configuration

The service will have access to both the variables from the .env file (if it exists) and the inline FOO variable.

Restart Policy

restart_policy: "on_failure"
retries: "5"
backoff: "5s"

These directives configure how systemg handles service failures:

• restart_policy: "on_failure": Automatically restart the service if it exits with a non-zero status code
• retries: "5": Attempt to restart the service up to 5 times before giving up
• backoff: "5s": Wait 5 seconds between restart attempts to avoid rapid restart loops

Running the Example

1. Navigate to the example directory:

   cd examples/hello-world

2. Create a .env file (optional):

   echo "EXAMPLE_VAR=value" > .env

3. Start the service:

   sysg start

4. Check the service status:

   sysg status

5. View the logs:

   sysg logs sh__hello_world

   You should see output like:

   Line number: 1
   Line number: 2
   Line number: 3
   ...

6. Stop the service:

   sysg stop

What You Learned

In this example, you learned how to:

• ✅ Create a basic systemg configuration file
• ✅ Run a shell script as a managed service
• ✅ Configure environment variables
• ✅ Set up automatic restart policies for fault tolerance
• ✅ Use basic systemg commands to manage services

Next Steps

Ready for a more realistic example? Check out the CRUD Application example to see how systemg can manage a full web application with cron jobs, database backups, and webhook notifications.