Adds docs for PowerShell Arrays with Icinga config

doc/05-Icinga-Integration.md

@@ -18,3 +18,4 @@ To get started, there are two ways to configure check command objects:
 
 * [Automated configuration](icingaintegration/01-Director-Baskets.md) with Baskets
 * [Manual configuration](icingaintegration/02-Manual-Integration.md) of check commands
+* [Using PowerShell Arrays in Icinga](icingaintegration/03-PowerShell-Arrays.md)

doc/icingaintegration/03-PowerShell-Arrays.md

@@ -0,0 +1,56 @@
+# Use PowerShell Arrays within Icinga Config
+
+For the [Icinga Director](https://icinga.com/docs/director/latest/) we do provide a config generator, allowing users to easily import `CheckCommands` directly into the Icinga infrastructure by using the `Director Baskets`.
+
+Some environments how ever do not make use of the Icinga Director and therefor require to handle PowerShell arrays as well.
+
+## PowerShell Arrays
+
+PowerShell arrays are usually defined as `@()` or together with `[array]`. In the end, the PowerShell is now expecting a comma separated input with your values.
+
+```powershell
+-ArrayArgument 'value1', 'value2', 'value3'
+```
+
+By default Icinga is not able to push arguments in this way and therefor we require a workaround
+
+## Icinga DSL for PowerShell arrays
+
+As Icinga is a very powerful solution and understands certain object types like arrays, we can make use of this.
+
+The easiest approach for integrating arguments into the PowerShell array handling, we can use the internal array handling of Icinga itself. This means from a configuration point we do not need to re-think our configuration or approach.
+
+Let's assume we have an argument called `-Services` within our check plugin which expects the `array` type. As we just learned that Icinga does understand the array data type and we can use it inside our configuration, we will continue with this approach.
+
+For this we will now write an Icinga DSL function and apply it to our `-Services` argument. We will use the custom variable `Icinga_Windows_Services` to store all our services we want to monitor on our service checks:
+
+```powershell
+"-Services" = {
+    value = {{
+        var arr = macro("$Icinga_Windows_Services$");
+
+        if (len(arr) == 0) {
+            return "$null";
+        }
+
+        return arr.join(",");
+    }}
+}
+```
+
+What we do here is to load the `Icinga_Windows_Services` into the variable `arr`. After that we will check if there are elements set inside the `arr` variable with `len(arr)`. If no value is inside, we will return `$null` to always set a value to the PowerShell.
+
+Last but not least we will glue every single value inside the array together by using `arr.join(",")` and separate it with a comma.
+
+For example if we are doing this inside your service configuration:
+
+```
+vars.Icinga_Windows_Services = [ "icinga2" ]
+vars.Icinga_Windows_Services += [ "w32time" ]
+```
+
+It will automatically be rendered during the runtime as this:
+
+```
+icinga2, w32time
+```