Part 2: Python bindings for models

Having a model is one thing. Using it requires you to ingest that model somewhere, apply values to its elements (leaves) as necessary/appropriate and then submit that completed model to the appliance for application to the config.

I’m a python guy, you might like Go, or ruby or whatever. thats up to you, but I use python right now, which means I use pyangbind and pyang to create pythonic modules I can import into a script, and then interact with the model attributes like I would any other object in python. We can then push that out to a device from that script.

This is more of a discovery post than anything particularly useful. It charts my adventure from a problem statement, through discovery of a solution, to a dead end. I post it here to help people see the logic I followed, and why, against all wisdom, it didn’t work.

Note that if you are familiar with YANG, I know why this is NOT the right way to do this, but I only know that having done this as shown here. Please don’t waste your time in the comments with nerdsplaining that to me. This is to show people a process and to help people who feel stupid when this stuff doesnt work, to see that they’re not alone. I learn by making mistakes.

Over the last few years I have spent a significant amount of time in YAML and Ansible. I’m not an expert by any means, but I can probably get anything I need done in maybe a few days worth of tinker time. I’m what you would call a fair weather scripter.

One thing I learned from building about 30,000 lines of YAML whilst orchestrating ACI, was that Ansible is a square peg, and everything networking is a round hole. Sometimes it fits, sometimes it doesn’t, but it is never perfect. Never.

Over the last two years or so, I have been on adventure with Data Centre Infrastructure renewal. As past posts may allude to, ACI was a big part of what we did, but before anyone gets all dogmatic about it, know that we didn’t go “All in” with that one product, since I personally don’t subscribe to the “DC Fabrics cure all ills” mantra.

CLOS fabrics and the various approaches to overlays within them are great at providing stable platforms with predictable properties for speed, latency and scale. Unsurprisingly, they go on to do a great job in server farms that can make the best use of that flexibility. During recent conversations on DC refresh, our Arista friends have been extremely keen to try and get us to run our Internet BGP border on the fabric as well. The 7280SR2K can handle 2M routes in FIB they say, just lob stuff into a VRF, bit of policy and voila. Yeah.

So I bought my ACI bundles so long ago that they’re still running 1.0(3f). Right now mainline is 1.2(1k), so i’m a bit behind.

Using the official Cisco doc I did the first staged upgrade from 1.0 to 1.1 using the Web GUI. I wanted to see what happened in a visual sense.

Basically you setup a connection between the APIC and a host that has staged the firmware files, then you setup a policy defining what versions the fabric should be on, and when that should be made active. For me it was 1.1(4f) and now basically.