Using AND/OR logic

InfraSonar's expression language allows you to combine multiple case statements using both AND logic (through nesting) and OR logic (through sequential case statements). This flexibility helps you define highly specific alert triggers.

AND Logic

When you nest case statements, they form an AND relationship. The inner case will only be evaluated if all preceding outer case conditions are met.

Suppose you want to raise an alert only when memory usage for some collector exceeds 80% AND the operating system is neither "Windows" nor "ChromeOS". You could achieve this by nesting:

// Raise a WARNING if memory usage > 80%
// AND the OS is NOT Windows
// AND the OS is NOT ChromeOS
case item.memory_usage_ratio > 0.8:
    case item.os != "Windows":
        case item.os != "ChromeOS":
            return WARNING, "Memory usage of @item.name exceeds 80%"
return OK

While functional, this nested approach can become less readable as more conditions are added, especially for exclusion logic.

OR Logic

A more elegant and readable way to handle exclusions or multiple conditions that lead to the same outcome is to use sequential case statements, which act as OR conditions. The first case statement that evaluates to true will be executed.

To achieve the same goal (alert when memory usage > 80%, but not for Windows or ChromeOS), we can place an early return statement for the excluded operating systems.

case item.os == "Windows":
case item.os == "ChromeOS":
    return // Exclude when "os" is Windows OR ChromeOS

// Test if memory usage exceeds 80 percent
case item.memory_usage_ratio > 0.8:
    return WARNING, "Memory usage of @item.name exceeds 80%"
return OK

This method improves readability and maintainability, especially when dealing with more complex exclusion criteria.