Global state (`get` and `set`)

By default, an expression only knows about the current item it is evaluating. The get and set functions allow you to share data across different items by storing values in a temporary "global state" during the check.

This is most commonly used to find inconsistencies (like version mismatches) or to aggregate totals (like summing CPU across a cluster).

Function Syntax

Function	Description	Syntax
`get`	Retrieves a value from the state.	`get('key', default_value)`
`set`	Saves a value to the state.	`set('key', value)`

Info

Note: get always requires a second argument as a default value. This value is used if the key hasn't been set yet (usually during the evaluation of the first item).

Example: Detecting Version Mismatch

In this scenario, we want to ensure all servers in a group are running the same software version. We "lock in" the version of the first server we see and compare every subsequent server against it.

// 1. Define the alert message
var.message = "
Version mismatch detected!
Reference: @var.name (v@var.version)
Conflict:  @item.name (v@item.version)
"

// 2. Try to get the reference data from previous items
var.name = get('ref_name', '')
var.version = get('ref_version', '')

// 3. Initialization: If name is empty, this is the FIRST item in the check.
case var.name == '':
    set('ref_name', item.name)
    set('ref_version', item.version)
    return OK

// 4. Comparison: Compare current item to the reference stored in state
case item.version != var.version:
    return ERROR, var.message

return OK

Best Practices

When using get and set to compare items, you should enable the "Single Alert" option in your check configuration.

Without it: You might get multiple separate alerts if several items fail the comparison.
With it: InfraSonar groups the results into a single consolidated notification.

Single Alert

A Single Alert auto-closes if the entire result is empty (no items), or if at least one expression returns OK while no other items trigger an alert.

Persistence Lifecycle

Values stored with set only persist for the duration of a single check run. Once the check completes and the final item is evaluated, the state is cleared. It will not interfere with the next time the check runs.

Advanced Aggregation

If you need to collect a list of all items that don't match, rather than just alerting on the first one found, see the append() function documentation.

Global state (get and set)