Icinga for Windows REST API calling tool

This is a lean alternative to the Icinga for Windows Exit-IcingaExecutePlugin PowerShell REST API client. It's useful to get rid of the performance penalty introduced by frequently calling powershell.exe from the agent.

Background

Icinga for Windows provides a icinga-powershell-framework and related icinga-powershell-plugins. Check plugins usually don't consume much resources on their own, but spinning up powershell.exe and initializing the Icinga framework is expensive. In normal operation mode, the Icinga agent would periodically execute each plugin as short lived child process. That multiplies the CPU time spent for no real use.

As mitigation, a separate long living PowerShell host daemon with a REST endpoint for check execution was invented by the Icinga team, where initialization is done only once, and plugins are then called as function rather than started as new process.

The agent would now just perform a cheap local HTTP POST to the daemon. In pracitce however it's not so cheap, because Icinga for Windows suggests to use yet another PowerShell function Exit-IcingaExecutePlugin to perform the HTTP POST, which basically reintroduces above problems.

This is where i4w_callapi helps: Get completely rid of PowerShell at agent side. Replace it with something that is optimized to safe resouces.

Installation

Preparation: Setup Icinga for Windows and enable it for REST API checks. Not documented here.

Compile - you can statically link the C runtime and get a self-contained binary for easy distribution.

RUSTFLAGS="-C target-feature=+crt-static"
cargo build --target=x86_64-pc-windows-msvc --release

Copy the binary into the agents bin path, which defaults to C:\Program Files\ICINGA2\sbin.

Usage

Execute your checks

Manual invokation example

> call_api_check.exe -c Invoke-IcingaCheckCPU -- -Warning 50 -Critical 90
[OK] Check package "CPU Load" | 'core_4'=3.378296%;50;90;0;100 'core_total'=3.948704%;50;90;0;100 'core_6'=3.345666%;50;
90;0;100 'core_5'=3.39417%;50;90;0;100 'core_7'=3.038184%;50;90;0;100 'core_0'=5.790892%;50;90;0;100 'core_2'=4.960417%;
50;90;0;100 'core_1'=3.999451%;50;90;0;100 'core_3'=3.682836%;50;90;0;100

In operation, the executable is intended to be used from a object CheckCommand definition.

object CheckCommand "PowerShell Base" {
   import "plugin-check-command"
   command = [ PluginDir + "/call_api_check.exe" ]
   arguments = {
       "--insecure" = {
            order = -3
            set_if = true
       }
       "--" = {
            order = -1
            set_if = true
        }
   }
   timeout = 3m
}

object CheckCommand "Invoke-IcingaCheckCPU" {
    import "PowerShell Base"
    arguments += {
        "-c" = {
            order = -2
            value = "Invoke-IcingaCheckCPU"
        }
        "-Warning" = {
            order = 1
            value = "$IcingaCheckCPU_Object_Warning$"
        }
        "-Critical" = {
            order = 2
            value = "$IcingaCheckCPU_Object_Critical$"
        }
        "-Core" = {
            order = 3
            value = "$IcingaCheckCPU_String_Core$"
        }
        "-NoPerfData" = {
            order = 99
            set_if = "$IcingaCheckCPU_SwitchParameter_NoPerfData$"
        }
        "-Verbosity" = {
            order = 4
            value = "$IcingaCheckCPU_Int32_Verbosity$"
        }
    }
    vars.IcingaCheckCPU_Object_Warning = "$$null"
    vars.IcingaCheckCPU_Object_Critical = "$$null"
    vars.IcingaCheckCPU_String_Core = "*"
    vars.IcingaCheckCPU_SwitchParameter_NoPerfData = false
    vars.IcingaCheckCPU_Int32_Verbosity = 0
}

Forwarded arguments syntax

There are two requirements that determine how call_api_check.exe must handle arguments after --

• call_api_check.exe wants to be a drop-in replacement for CheckCommand "PowerShell Base" and therefore has to cope with the arguments += { /* ... */ } part generated by Icinga Director.
• PowerShell check plugins want their parameters in certain structure and data type. The REST API expects this structure and type in the JSON request.

In consequence call_api_check.exe has to parse and translate PowerShell syntax (e.g. as generated by Icinga Director) into JSON objects. Currently the following syntax is syntax is supported:

Forwarded command line argument	Resulting data type of the argument value
-MyArg	boolean true
-MyArg "foo"	string foo
-MyArg foo	string foo
-MyArg 123	number 123
-MyArg foo,123	Array [string foo, number 123]
-MyArg "foo,123"	Array [string foo, number 123]
-MyArg ["foo",123]	Array [string foo, number 123]
-MyArg @("foo",123)	Array [string foo, number 123]
-MyArg [ foo , [ 123 , 456 ] ]	Array [ string foo, Array [number 123, number 456] ]
-MyArg $False,$True	Array [boolean false, boolean true]
-MyArg '"foo"'	string "foo" - double quotes preserved as part of string because surrounding single quotes disable special characters
-MyArg "foo`""	string foo" - backticks escapes special characters
-MyArg (ConvertTo-IcingaSecureString 'my string')	string (ConvertTo-IcingaSecureString 'my string') - parantheses receive special handling at API side