Custom link to run a script right away

[markkuleinio]

I'm figuring out a way to provide a custom link to run a NetBox script. This is for prefix model, and the purpose of the script is to provide user some externally-retrieved extra information about the prefix.

I see that I can create a custom script, and then create a custom link with the script URL (with the prefix/ID given as a URL parameter). But when clicking the custom link the user then gets the normal script run page:

"
Script Data
(the URL parameter data field(s))
Script Execution Parameters
Commit changes
Commit changes to the database (uncheck for a dry-run)
Cancel - Run Script
"

Also the output after running the script is suboptimal, showing the technical data of running the script in addition to the "console" output of the script.

What I would like to get is that the script runs right away when the link is clicked, and the user gets shown the resulting output, which is not NetBox data but something else, basically some nicely formatted read-only table output.

How could a plugin be used to provide this functionality?

To be clear, I don't want to integrate the output of the script right into the prefix page because retrieving the data is expensive (in terms of execution time and external resource usage), so I need the data to be retrieved and shown on a separate page only when clicking the custom link.

Almost all the plugins I've browsed seem to implement their own data models and thus show the database contents, or they integrate in the object pages and show some data pane over there. I haven't found a "Hello, World!" page output plugin yet (*) 😃 So I'm kind of lost right in the start already.

The Nagios plugin listed in https://github.com/netbox-community/netbox/wiki/Plugins comes closest yet: it retrieves and shows external data (not data from NetBox database), but it shows it within the device page, not in a separate URL/page.

When thinking about the plugin approach, I guess it is something like this:

• The plugin provides a URL that accepts the prefix/ID as URL parameter (this is used and clicked in the custom link) (I think this is something that is configured in the plugin's urls.py)
• When the URL is requested, the plugin code then executes, reads the URL parameter and does its external magic
• The plugin returns output (in a view? form? using a template) that consists of the resulted data, within the NetBox' normal GUI
• User uses the normal browser back button to go back to the prefix

Do you have any pointers or helpful comments to proceed? I'm willing to publish the "Hello, World!" page plugin if this succeeds 🙂

(*) I did find this: https://github.com/cruse1977/netbox-plugin-helloworld, which exposes a NetBox API URL and returns JSON output.

[markkuleinio]

Well, what do you know, I read the documentation once more and realized some hints that were not model-dependent, and managed to do this:

So, I think I have something here...

[markkuleinio]

There it is now, netbox_hello_world_page plugin:

https://github.com/markkuleinio/netbox-hello-world-page

Feel free to add this to the plugins wiki page if it looks useful for someone.

[markkuleinio]

Now, maybe someone with more NetBox plugins experience can explain this:

Since installing this plugin in my test instance the loading of NetBox frontpage has started taking 75 seconds, occasionally.

What could cause this? The plugin does not load anything, and shouldn't execute when the frontpage is accessed.

Setting DEBUG = True affects something because then I'm not able to get this issue when clicking the NetBox icon in the frontpage anymore. Otherwise it is quite easy to get it happen. I'll have to do some tcpdumps I guess.

[markkuleinio]

Dumped the traffic (both between client and Nginx, and between Nginx and uWSGI). The problem seems to be in the client side:

• When it works, the browser (Firefox or MS Edge) gets the changelog (as configured in the dashboard) right after getting the frontpage.
• When it doesn't work. the browser first gets the frontpage, then it just does nothing (sends keepalives every 10 seconds), until the web server (not NetBox) FINs the connection after 75 seconds. Then the browser opens a new TCP session and gets the changelog.

If I disable the plugin, there is never a problem.

If I enable the debug mode, there is never a problem.

When the plugin is enabled and debug is disabled, let's say very many of all frontpage loads cause the browser to wait.

If I hide the plugin menu (by renaming the menu object in navigation.py to something else), there is again no problem.

--> Having the plugin menu item in the screen causes some strange behavior in the browser.

[markkuleinio]

The 75 seconds comes from the default keepalive_timeout value in Nginx: http://nginx.org/en/docs/http/ngx_http_core_module.html#keepalive_timeout

If I set it to 15 seconds, then the browser waits 15 seconds and then Nginx FINs the connection --> browser opens a new TCP connection and requests the changelog on that.

--> Why doesn't the browser want to send the second request and keeps on waiting for nothing?

[markkuleinio]

I also checked the request and response headers in both connections, and did not see any difference between working and not working cases --> the browser behavior change is based on the page contents, not based on the headers.

Also, tested with uWSGI and Gunicorn, in both cases it looks the same (quite natural as it still seems to be a content/browser issue).

[markkuleinio]

Ok... due to unexpected circumstances (= I made poor choices when upgrading Debian+Postgresql) I had to delete the whole database and create a new empty database. And guess what: I cannot reproduce the wait issue anymore.

Well, I'll let you know if the problem occurs again.