hostname cleanup does not work as intended (CMK_JINJA_USE_REPLACERS_FOR_HOSTNAMES)

[Meyric]

Does "CMK_JINJA_USE_REPLACERS_FOR_HOSTNAMES" in the config.py / cmk_cleanup_hostname(input_str) in application/modules/checkmk/helpers.py work properly?

It seems like i dont get it running properly.

little explanation what i am trying to do/Context:
I am using CMDBSyncer to sync hosts from NetBox to Checkmk. During the sync process:

• Hosts are imported into CMDBSyncer from NetBox with their original names (this works as intended and should remain unchanged in CMDBSyncer).
• However, I would like to rewrite the hostname only during the export to Checkmk, as some hostnames do not match Checkmk's required pattern: '^[-0-9a-zA-Z_.]+\\\\Z'

I changed following two lines in the config.py

    CMK_JINJA_USE_REPLACERS = True
    CMK_JINJA_USE_REPLACERS_FOR_HOSTNAMES = True

in the helpers.py the comment [...] you wan't to use as tag_id in cmk is wrong, :

def cmk_cleanup_hostname(input_str):
    """
    Cleans Invalid Chars out
    of strings you wan't to use as tag_id in cmk
    """
    if app.config['CMK_JINJA_USE_REPLACERS_FOR_HOSTNAMES']:
        for needle, replacer in app.config['REPLACERS']:
            input_str = input_str.replace(needle, replacer)
    return re.sub('[^a-zA-Z0-9_-]', '_', input_str.strip()).lower()

maybe i am missing something?
I also tried to create some rules, but they dont change the Hostname, they just add an Attribute named Hostname with the cleaned-up hostname as value.

I found a workaround, after editing application/modules/checkmk/syncer.py it work - but i dont know if this is the right implementation:

#   .-- Run Sync
    def run(self):
        """Run Job"""
        # In Order to delete Hosts from Checkmk, we collect the ones we sync
[...]
            self.console = progress.console.print
            for hostname, data in host_actions.items():

#added following 2 lines
                 if app.config['CMK_JINJA_USE_REPLACERS_FOR_HOSTNAMES']:
                    hostname = cmk_cleanup_hostname(hostname)

                export_details = []
                progress.console.print(f"* {hostname}")
[...]

Or is this feature not 100% implemented right now?

[Bastian-Kuhn]

Hi @Meyric

First, never change the config.py, you can use local_config.py to override Syncer config, see here. This is important for updates.

Thanks for the hint to the wrong Doc string, is fixed in git.

About the Replacement, that is not that well documented yet, will fix that too.

It's meant to be used as a Jinja Function. With CMK_JINJA_USE_REPLACERS... you just set to use the additional Replaces which you can configure too in the config, but always will it use the regex to make the hostname a valid Checkmk one.

This Function then can be currently used in every field, which supports Jinja.
The Feature was not developed for your scenario, the customer I built it for used it to clean up Hostnames he wanted downtimes for.

Your workaround is fine for now, but to solve your Problem, I need another solution.

I need to think about the Impacts when the Host has a different name in Checkmk as in Syncer.
Specially, it also needs to work, for example when you want to do the inventory.

Maybe the Solution is as simple, as to apply the function generally on the Hostnames for Checkmk Operations.
Because it could not break anything which not already is broken (invalid hostnames).

What do you think?

[Meyric]

Hi @Bastian-Kuhn,

thanks for the reply and the helpful hints.

After giving it some more thought, I realized it might make sense to validate hostnames for compliance with the expected pattern (no invalid characters like ":", "@", etc.) right at the start of the import process. This could help prevent invalid hostnames from being propagated through the system.

In the current setup, "names" from NetBox are displayed in CMDBSyncer as "Hostname", even if they are invalid as a Hostname. This means that invalid hostnames are already present in CMDBSyncer, even though they will not work properly in Checkmk (or anywhere else, where it checks if its a valid Hostname). To ensure consistency and avoid confusion, it would be helpful to validate hostnames during the import into CMDBSyncer.

I suggest introducing an optional configuration flag (sth. like NETBOX_CHECK_VALID_HOSTNAME) in the local_config.py. If enabled, this flag would:

• Check each hostname during the import process to ensure it matches a valid hostname pattern (a-z A-Z 0-9 -).
• Skip or reject invalid hostnames with a clear error message (sth. like "Invalid hostname: [hostname]. Please update it in NetBox.").

This way, invalid hostnames are identified and fixed earlier in the process, ensuring that CMDBSyncer and Checkmk operate with consistent and valid data. For those who prefer not to enforce hostname validation, the feature can simply remain disabled in the local_config.py, ensuring backward compatibility.

I am aware that there is a rewrite function available for the import process from NetBox to CMDBSyncer. However, I prefer not to rewrite the hostnames, as they should remain consistent with their representation in NetBox.

What do you think about this approach?

[Bastian-Kuhn]

Hi @Meyric

Yes, right in front of imports such a function but with a switch to deactivate it globally.
I would have it as a default activated if object type of Account is set to host because a Hostname needs to by valid in any case.

So if another Object Type is set, no validation.

Will implement that soon. Makes total sense to have it.

[Bastian-Kuhn]

It's already implemented since it was quick to do.

If in Account, object host is set:

The import will not import a device, which has an invalid name, but log it:

[Meyric]

Hi @Bastian-Kuhn,

that was quick, thanks!
I tried it right now, seems to work. nice!