icinga2/doc/20-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.

You can also attach the script debugger to the configuration validation:

# icinga2 daemon -C -X

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

• Configuration errors e.g. apply rules
• 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 variable 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

Debugging API Filters

Queries against the Icinga 2 REST API can use filters, just like available in assign where expressions. If these filters cause an internal error, they return an empty result to the caller.

In order to analyse these server-side errors, you can use the script debugger.

The following example tries filter for all host objects where the custom variable os is set. There are various possibilities to check that, one of them would be host.vars.os != "". Another idea is to use the contains method on the custom attribute dictionary like this: host.vars.contains("os").

$ curl -k -s -u root:icinga -H 'Accept: application/json' -H 'X-HTTP-Method-Override: GET' \
 -X POST 'https://localhost:5665/v1/objects/services' \
 -d '{ "filter": "host.vars.contains(\"os\")", "attrs": [ "__name" ], "joins": [ "host.name", "host.vars" ], "pretty": true }'

This will fail on all hosts which don't have any custom variable specified.

# icinga2 daemon -X

Breakpoint encountered.
Exception: Error: Argument is not a callable object.
Location: in <API query>: 1:0-1:23
You can inspect expressions (such as variables) by entering them at the prompt.
To leave the debugger and continue the program use "$continue".

<1> => this.host

...

    	vars = null

<2> => $continue

By definition, a type method can only be invoked on an actual object.

In order to stay safe, add more checks to the API filter:

• host.vars && host.vars.contains("os") or
• host.vars && typeof(host.vars) == Dictionary && host.vars.contains("os")

Example:

$ curl -k -s -u root:icinga -H 'Accept: application/json' -H 'X-HTTP-Method-Override: GET' \
 -X POST 'https://localhost:5665/v1/objects/services' \
 -d '{ "filter": "host.vars && typeof(host.vars) == Dictionary && host.vars.contains(\"os\")", "attrs": [ "__name" ], "joins": [ "host.name", "host.vars" ], "pretty": true }'