Filter function for assign where
- The function should only take a dictionary as parameter, not the entire host object itself. This leaves away hardcoding host.vars.int all over.
- Give the parameters and variables telling names. For a function, you’ll type them just once.
- The typeof() checks are already awesome, maybe add some log() calls for better troubleshooting
Standalone config below.
object Host "<mySwitch>" {
check_command = "dummy"
vars.int["Port 0/1"] = {
int = "gigabitethernet1/0/1"
port_type = "uplink"
}
vars.int["Port 0/2"] = {
int = "gigabitethernet1/0/2"
port_type = "workstation"
}
}
globals.check_int_port_type = function(interfaces, port_type) {
if (typeof(interfaces) != Dictionary) {
log(LogWarning, "check_int_port_type", "interfaces parameter is not a Dictionary, but " + typeof(interfaces).to_string() + " (value: '" + Json.encode(interfaces) + "')")
return false
}
for (ifname => ifvalues in interfaces) {
log(LogInformation, "check_int_port_type", "Evaluating interface " + ifname + " with values: '" + Json.encode(ifvalues) + "'")
if (typeof(ifvalues) == Dictionary && ifvalues.port_type == port_type) {
log(LogInformation, "check_int_port_type", "Matched port_type: " + port_type)
return true
}
}
return false
}
Doesn’t satisfy yet, but looks better.
- If I would need to negate a function boolean return value, why not just use
ignore where. We’re already in a for loop anyways.
/* use this service definition for any port type other than a workstation */
apply Service for (int => config in host.vars.int) {
check_command = "dummy"
vars += config
ignore where check_int_port_type(host.vars.int, "workstation") // <--- this for the exclusion, and the changed function parameter
}
/* use this service definition for workstations */
apply Service "Workstation: " for (int => config in host.vars.int) {
check_command = "dummy"
vars += config
assign where check_int_port_type(host.vars.int, "workstation") // <--- and this, just using the different function argument here
}
Doesn’t work yet though, as the function always returns true, since we loop in there again over all interfaces, and one always is the workstation key. Though we’ve learned that from programming the DSL now, with fancy logs.
information/ApiListener: My API identity: imagine
information/check_int_port_type: Evaluating interface Port 0/1 with values: '{"int":"gigabitethernet1/0/1","port_type":"uplink"}'
information/check_int_port_type: Evaluating interface Port 0/2 with values: '{"int":"gigabitethernet1/0/2","port_type":"workstation"}'
information/check_int_port_type: Matched port_type: workstation
information/check_int_port_type: Evaluating interface Port 0/1 with values: '{"int":"gigabitethernet1/0/1","port_type":"uplink"}'
information/check_int_port_type: Evaluating interface Port 0/2 with values: '{"int":"gigabitethernet1/0/2","port_type":"workstation"}'
information/check_int_port_type: Matched port_type: workstation
information/check_int_port_type: Evaluating interface Port 0/1 with values: '{"int":"gigabitethernet1/0/1","port_type":"uplink"}'
information/check_int_port_type: Evaluating interface Port 0/2 with values: '{"int":"gigabitethernet1/0/2","port_type":"workstation"}'
information/check_int_port_type: Matched port_type: workstation
information/check_int_port_type: Evaluating interface Port 0/1 with values: '{"int":"gigabitethernet1/0/1","port_type":"uplink"}'
information/check_int_port_type: Evaluating interface Port 0/2 with values: '{"int":"gigabitethernet1/0/2","port_type":"workstation"}'
information/check_int_port_type: Matched port_type: workstation
Doesn’t work here
Pre-filter data for apply for rules
Ok, new idea with the function pre-filtering all data. This is a little brainfuck since you need to supply two conditions:
- exclude a specific port_type (best to be matched with a filter) which means cutting it off the dictionary
- include a specific port_type (and only this, or go by a wildcard pattern match), only returning this as a result
In order to avoid two different functions, I’ve developed a function which takes the port_type_filter and controls exclude or include with a boolean parameter.
This is the function signature.
globals.get_host_interfaces = function(interfaces, port_type_filter, exclude_enabled) {
This can then be used inside the service apply rules, shortcut and simple.
/* use this service definition for any port type other than a workstation */
apply Service for (int => config in get_host_interfaces(host.vars.int, "*workstation*", true)) {
check_command = "dummy"
vars += config
}
/* use this service definition for workstations */
apply Service "Workstation: " for (int => config in get_host_interfaces(host.vars.int, "*workstation*", false)) {
check_command = "dummy"
vars += config
}
Filter specific nested dictionary keys in a function
I’m using lots of logging for development here, this keeps it simple to know if conditions are matched, and at which place a problem might occur.
I’m also a fan of re-using any DSL feature which makes programming easier. Especially for complex value types like a Dictionary, a JSON encoded string is similar to Perl’s Data::Dumper or PHP’s var_dump().
First, define the result storage.
var res = {}
Then check for specific parameter values, if they do meet our requirements. If not, return an empty result. This makes apply for think that no objects matched. Log something for better error handling.
if (typeof(interfaces) != Dictionary) {
log(LogWarning, "get_host_interfaces", "interfaces parameter is not a Dictionary, but " + typeof(interfaces).to_string() + " (value: '" + Json.encode(interfaces) + "')")
return res // empty
}
Loop through the interfaces we’ve gotten as interfaces parameter. Log some debug information to see which values are currently processed.
for (ifname => ifvalues in interfaces) {
log(LogInformation, "get_host_interfaces", "Evaluating interface " + ifname + " with values: '" + Json.encode(ifvalues) + "'")
If the nested dictionary is not of the type Dictionary, avoid to process any further and just return. The user must fix the configuration then.
if (typeof(ifvalues) != Dictionary) {
log(LogInformation, "get_host_interfaces", "Wrong type for ifvalues for ifname + " + ifname)
return {}
}
Add some debug logging to see whether excluding or including port types is enabled (you can leave that away, it just helps with the logging chain).
log(LogInformation, "get_host_interfaces", "Port_type_filter: " + port_type_filter + " ifvalues.port_type: " + ifvalues.port_type)
if (exclude_enabled) {
log(LogInformation, "get_host_interfaces", "exclude enabled")
} else {
log(LogInformation, "get_host_interfaces", "exclude disabled")
}
If the first condition is matched, which means that exclude the given filter if matching on the port_type attribute, then we want to store the ifvalues from the nested dictionary just again in our result storage res with the same key ifvalues. Add some logging to see what’s stored.
if (exclude_enabled == true && !match(port_type_filter, ifvalues.port_type)) {
log(LogInformation, "get_host_interfaces", "Matched port_type: " + ifvalues.port_type)
res[ifname] = ifvalues
log(LogInformation, "get_host_interfaces", "Adding to result: " + Json.encode(res))
If the second condition is matched, which means that include the given filter if matching in the port_type attribute, then we want to store the values in a similar manner just like above. Again, specific scoped logging so that I know which condition is currently met.
} else if (exclude_enabled == false && match(port_type_filter, ifvalues.port_type)) {
log(LogInformation, "get_host_interfaces", "Matched port_type: " + ifvalues.port_type)
res[ifname] = ifvalues
log(LogInformation, "get_host_interfaces", "Adding to result: " + Json.encode(res))
Add an else condition, just to log if something doesn’t match at all. This helps to refine the filters. The reason I am going for a wildcard pattern match here is that you may want to re-use this function for other apply rules, where the port_type isn’t necessarily only “workstation”. Or do whatever with it 
} else {
log(LogInformation, "get_host_interfaces", "Nothing matched")
}
Finally, log the result in res again, to see where we are at, then return the value. This is what the apply for rule actually gets for processing in the for loop. If your brain didn’t explode yet, continue implementing it.
}
log(LogInformation, "get_host_interfaces", "Result: " + Json.encode(res))
return res
}
Tests
Now let’s see what happens with that code.
information/get_host_interfaces: Evaluating interface Port 0/1 with values: '{"int":"gigabitethernet1/0/1","port_type":"uplink"}'
information/get_host_interfaces: Port_type_filter: *workstation* ifvalues.port_type: uplink
information/get_host_interfaces: exclude enabled
information/get_host_interfaces: Matched port_type: uplink
information/get_host_interfaces: Adding to result: {"Port 0/1":{"int":"gigabitethernet1/0/1","port_type":"uplink"}}
information/get_host_interfaces: Evaluating interface Port 0/2 with values: '{"int":"gigabitethernet1/0/2","port_type":"workstation"}'
information/get_host_interfaces: Port_type_filter: *workstation* ifvalues.port_type: workstation
information/get_host_interfaces: exclude enabled
information/get_host_interfaces: Nothing matched
information/get_host_interfaces: Result: {"Port 0/1":{"int":"gigabitethernet1/0/1","port_type":"uplink"}}
information/get_host_interfaces: Evaluating interface Port 0/1 with values: '{"int":"gigabitethernet1/0/1","port_type":"uplink"}'
information/get_host_interfaces: Port_type_filter: *workstation* ifvalues.port_type: uplink
information/get_host_interfaces: exclude disabled
information/get_host_interfaces: Nothing matched
information/get_host_interfaces: Evaluating interface Port 0/2 with values: '{"int":"gigabitethernet1/0/2","port_type":"workstation"}'
information/get_host_interfaces: Port_type_filter: *workstation* ifvalues.port_type: workstation
information/get_host_interfaces: exclude disabled
information/get_host_interfaces: Matched port_type: workstation
information/get_host_interfaces: Adding to result: {"Port 0/2":{"int":"gigabitethernet1/0/2","port_type":"workstation"}}
information/get_host_interfaces: Result: {"Port 0/2":{"int":"gigabitethernet1/0/2","port_type":"workstation"}}
That’s good, we have two apply for rule calls here, and both of them loop over the host object interfaces with two of them, makes it four evaluation rounds.
We can also see that 2 conditions matched, 2 did not. That’s what I’ve expected.
Now let’s verify this with object list:
imagine /etc/icinga2/tests # icinga2 object list --type Service
Object '<mySwitch>!Port 0/1' of type 'Service':
% declared in '/etc/icinga2/tests/watermelon.conf', lines 65:1-65:94
* __name = "<mySwitch>!Port 0/1"
* action_url = ""
* check_command = "dummy"
% = modified in '/etc/icinga2/tests/watermelon.conf', lines 66:3-66:25
* check_interval = 300
* check_period = ""
* check_timeout = null
* command_endpoint = ""
* display_name = "Port 0/1"
* enable_active_checks = true
* enable_event_handler = true
* enable_flapping = false
* enable_notifications = true
* enable_passive_checks = true
* enable_perfdata = true
* event_command = ""
* flapping_threshold = 0
* flapping_threshold_high = 30
* flapping_threshold_low = 25
* groups = [ ]
* host_name = "<mySwitch>"
% = modified in '/etc/icinga2/tests/watermelon.conf', lines 65:1-65:94
* icon_image = ""
* icon_image_alt = ""
* max_check_attempts = 3
* name = "Port 0/1"
% = modified in '/etc/icinga2/tests/watermelon.conf', lines 65:1-65:94
* notes = ""
* notes_url = ""
* package = "_etc"
% = modified in '/etc/icinga2/tests/watermelon.conf', lines 65:1-65:94
* retry_interval = 60
* source_location
* first_column = 1
* first_line = 65
* last_column = 94
* last_line = 65
* path = "/etc/icinga2/tests/watermelon.conf"
* templates = [ "Port 0/1" ]
% = modified in '/etc/icinga2/tests/watermelon.conf', lines 65:1-65:94
* type = "Service"
* vars
% = modified in '/etc/icinga2/tests/watermelon.conf', lines 67:3-67:16
* int = "gigabitethernet1/0/1"
* port_type = "uplink"
* volatile = false
* zone = ""
No name prefix, as obviously port_type = "uplink". Good.
Object '<mySwitch>!Workstation: Port 0/2' of type 'Service':
% declared in '/etc/icinga2/tests/watermelon.conf', lines 71:1-71:111
* __name = "<mySwitch>!Workstation: Port 0/2"
* action_url = ""
* check_command = "dummy"
% = modified in '/etc/icinga2/tests/watermelon.conf', lines 72:3-72:25
* check_interval = 300
* check_period = ""
* check_timeout = null
* command_endpoint = ""
* display_name = "Workstation: Port 0/2"
* enable_active_checks = true
* enable_event_handler = true
* enable_flapping = false
* enable_notifications = true
* enable_passive_checks = true
* enable_perfdata = true
* event_command = ""
* flapping_threshold = 0
* flapping_threshold_high = 30
* flapping_threshold_low = 25
* groups = [ ]
* host_name = "<mySwitch>"
% = modified in '/etc/icinga2/tests/watermelon.conf', lines 71:1-71:111
* icon_image = ""
* icon_image_alt = ""
* max_check_attempts = 3
* name = "Workstation: Port 0/2"
% = modified in '/etc/icinga2/tests/watermelon.conf', lines 71:1-71:111
* notes = ""
* notes_url = ""
* package = "_etc"
% = modified in '/etc/icinga2/tests/watermelon.conf', lines 71:1-71:111
* retry_interval = 60
* source_location
* first_column = 1
* first_line = 71
* last_column = 111
* last_line = 71
* path = "/etc/icinga2/tests/watermelon.conf"
* templates = [ "Workstation: Port 0/2" ]
% = modified in '/etc/icinga2/tests/watermelon.conf', lines 71:1-71:111
* type = "Service"
* vars
% = modified in '/etc/icinga2/tests/watermelon.conf', lines 73:3-73:16
* int = "gigabitethernet1/0/2"
* port_type = "workstation"
* volatile = false
* zone = ""
Name prefix "Workstation: " as obviously port_type = "workstation".
Awesome, it works 
Working configuration
Attached is the full configuration, works standalone. Just include it in your icinga2.conf and drop all other config object includes.
mkdir -p /etc/icinga2/tests
vim /etc/icinga2/tests
include "tests/watermelon.conf"
watermelon.conf.txt (2.4 KB)