icinga2/doc/19-script-debugger.md

Script Debugger

You can run the Icinga 2 daemon with the -X (--script-debugger) parameter to enable the script debugger:

# icinga2 daemon -X

When an exception occurs or the debugger keyword is encountered in a user script, Icinga 2 launches a console that allows the user to debug the script.

Here is a list of common errors which can be diagnosed with the script debugger:

• Configuration errors (apply)
• Errors in user-defined functions

Debugging Configuration Errors

The following example illustrates the problem of a service apply rule which expects a dictionary value for config, but the host custom attribute only provides a string value:

object Host "script-debugger-host" {
  check_command = "icinga"

  vars.http_vhosts["example.org"] = "192.168.1.100" // a string value
}

apply Service for (http_vhost => config in host.vars.http_vhosts) {
  import "generic-service"

  vars += config // expects a dictionary

  check_command = "http"
}

The error message on config validation will warn about the wrong value type, but does not provide any context which objects are affected.

Enable the script debugger and run the config validation:

# icinga2 daemon -C -X

Breakpoint encountered in /etc/icinga2/conf.d/services.conf: 59:67-65:1
Exception: Error: Error while evaluating expression: Cannot convert value of type 'String' to an object.
Location:
/etc/icinga2/conf.d/services.conf(62):   check_command = "http"
/etc/icinga2/conf.d/services.conf(63):
/etc/icinga2/conf.d/services.conf(64):   vars += config
                                         ^^^^^^^^^^^^^^
/etc/icinga2/conf.d/services.conf(65): }
/etc/icinga2/conf.d/services.conf(66):
You can inspect expressions (such as variables) by entering them at the prompt.
To leave the debugger and continue the program use "$continue".
<1> =>

You can print the variables vars and config to get an idea about their values:

<1> => vars
null
<2> => config
"192.168.1.100"
<3> =>

The vars attribute has to be a dictionary. Trying to set this attribute to a string caused the error in our configuration example.

In order to determine the name of the host where the value of the config variable came from you can inspect attributes of the service object:

<3> => host_name
"script-debugger-host-01"
<4> => name
"http"

Additionally you can view the service object attributes by printing the value of this.

Using Breakpoints

In order to halt execution in a script you can use the debugger keyword:

object Host "script-debugger-host-02" {
  check_command = "dummy"
  check_interval = 5s

  vars.dummy_text = {{
    var text = "Hello from " + macro("$name$")
    debugger
    return text
  }}
}

Icinga 2 will spawn a debugger console every time the function is executed:

# icinga2 daemon -X
...
Breakpoint encountered in /etc/icinga2/tests/script-debugger.conf: 7:5-7:12
You can inspect expressions (such as variables) by entering them at the prompt.
To leave the debugger and continue the program use "$continue".
<1> => text
"Hello from script-debugger-host-02"
<2> => $continue