Scripting with LUA

Monsta allows you to create custom logic for data collection, metric processing and complex alert rules using the programming language Lua.

If the default templates or native expressions are not sufficient for your needs (such as parsing complex strings, advanced mathematical calculations or loops), the Lua scripting engine offers full flexibility to extend the platform.

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Why Lua?

Lua is a Brazilian scripting language, widely used in the technology industry (especially in games and embedded systems) for three main reasons:

• Extreme Speed: It is one of the fastest scripting languages in the world, guaranteeing that your scripts run in milliseconds without overloading the Monsta server.
• Lightweight: The interpreter takes very little memory space, allowing large-scale concurrent executions.
• Simple Syntax: It is very easy to read and learn, even for those with little programming experience.

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Quick Lua Syntax Guide

To help you get started creating your first scripts in Monsta, here are the fundamental language concepts:

Variables and Data Types

In Lua, you don’t need to define the variable type beforehand (dynamic typing). Always use the local keyword to ensure the variable exists only within that script (avoiding memory conflicts).

local nome_dispositivo = "Servidor Core" -- String
local latencia = 45                     -- Number
local ativo = true                      -- Boolean

Conditional Structures (if / else)

The syntax uses the keywords then, elseif and requires closing the block with an end.

if latencia > 100 then
    print("Alerta: Latência Alta!")
elseif latencia > 50 then
    print("Aviso: Latência Moderada.")
else
    print("Status: OK.")
end

Tables (Dictionaries and Arrays)

Tables are the only complex data structure in Lua. They serve both as indexed lists and as key-value objects.

-- Example of Array/List
local sensores = {"Ping", "CPU", "Memória"}

-- Example of Dictionary (Key/Value)
local dados_coleta = {
    ip = "192.168.1.50",
    status = "Online",
    portas_abertas = 4
}

Be careful with indices!

Unlike most programming languages (such as JavaScript or Python) where lists start at index 0, in Lua tables start at index 1. Therefore, sensores[1] will return “Ping”.

How does Monsta interact with the script?

Usually, Monsta injects global variables or pre-defined tables into your script (containing the data collected from the device) and expects your script to return a specific value (such as a number, text, or boolean) using the return command.

-- Example of an SNMP query
local load_linux = snmp.get("1.3.6.1.4.1.2021.10.1.3.2.0") -- Monsta function
return load_linux

Resources and Complete Manuals

To dive deeper into the language, consult the official Lua language documentation.

Monsta has its own functions that are used in scripts. To learn about the specific internal modules that Monsta provides (network functions, string manipulation and connection), check the next articles in this area (Lua Script Modules).