NetBox / Source of Truth

Why Model Your Network as Data? The Source-of-Truth Problem

Advanced11 min read

What you'll learn

The real limitation of hand-maintained inventory files at scale
What 'source of truth' means as a data-modeling problem, not an execution problem
A preview, real and verified, of what this module builds toward
That this module is not about re-executing tasks -- it's about where inventory comes from

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Every fleet so far has lived in one file, maintained by hand

A different kind of problem than execution

Nornir (Phase 3.4) answers how do I execute across many devices. NAPALM (Phase 3.5) answers how do I normalize what I get back. Multi-vendor Automation (Phase 3.6) answers how do I select the right driver automatically. None of them ever asked: where does the list of devices itself come from? Every one of them read hosts.yaml, written by a person, by hand.

Static inventory -- every module since Phase 2.6

hosts.yaml / devices.csvwritten and updated by hand
Adding a deviceedit the file, redeploy it everywhere it's used
No relationships, no query languagejust rows

NetBox -- a real source of truth

Structured recordssites, devices, interfaces, IPs -- related, not flat
Adding a deviceone record, in one place
Every automation script reads the same live source

Quick checkConcept check

What question does this module answer that Nornir, NAPALM, and Multi-vendor Automation never asked?

How do I run a task faster?Where does the inventory itself come from, and what happens when it needs to change?How do I normalize get_facts() output?How do I select the right NAPALM driver?

A real, verified preview

What this module proves, concretely, by its capstone

This isn't a promise -- it's already been verified in this authoring environment. Adding one device record to a NetBox-shaped backend, with zero local YAML file touched, changes what a real Nornir inventory plugin loads on the very next run.

output — real, verified (Lesson 6 builds this in full)

Before adding a device to NetBox: ['SW1', 'SW2', 'SW3']
After adding SW4 in NetBox (no local file changed): ['SW1', 'SW2', 'SW3', 'SW4']

Real, verified output. No hosts.yaml existed anywhere in this test -- the inventory came entirely from NetBox records, and grew the moment a new record was added.

Quick checkPredict output

Based on the real, verified output above, what would a learner need to do to add SW4 to a NetBox-backed Nornir inventory?

Edit hosts.yaml and redeploy it to every script that uses itAdd one device record in NetBox -- nothing local changes, and the next InitNornir() run picks it up automaticallyRestart Nornir's own package installationNothing -- new devices are never picked up automatically

What this module reuses, and what's genuinely new

Not re-taught here

InitNornir(), nr.run(), filtering, and concurrency (Phase 3.4) are assumed known. get_facts()/get_interfaces() and NAPALM's normalized shapes (Phase 3.5) are assumed known. nornir_napalm and automatic driver selection (Phase 3.6) are assumed known. This module adds exactly one new layer underneath all of them: where the inventory itself comes from.

Quick checkScenario

A learner expects this module to re-explain nr.run() or get_facts() from scratch. What should they expect instead?

A full repeat of Nornir and NAPALM fundamentalsThose are prerequisites, reused not re-taught -- this module's new material is entirely about the source of the inventory itself, connecting to a real Nornir inventory plugin that reads from NetBox instead of static YAMLThis module replaces Nornir entirelyThis module doesn't use Nornir at all

Quick checkConcept check

Is 'source of truth' primarily about running automation faster or more reliably?

Yes -- it's a performance optimizationNo -- it's about having one authoritative, structured, queryable place that inventory-consuming automation reads from, instead of a hand-maintained file that can silently drift out of dateIt's about replacing Python with a database query languageIt's a synonym for concurrency

Key takeaways

Every module since Phase 2.6 has assumed a correct, hand-maintained hosts.yaml already exists -- this module questions that assumption directly.
Source of truth means one authoritative, structured, queryable place inventory comes from -- a data-modeling problem, not an execution problem.
A real, verified preview: adding one NetBox device record changed what a real Nornir inventory plugin loaded, with zero local file touched -- this module's capstone builds that in full.
Nornir, NAPALM, and nornir_napalm mechanics are all prerequisites here, reused not re-taught -- only the inventory source itself is new.

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NetBox's Data Model: Sites, Devices, Interfaces, IP Addresses

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