## Why
With several PuppetDBs behind one endpoint, consumers cannot tell which backend a node's data came from.
## How
- Add a synthetic `pdbmux_source` fact per certname on `/facts`, valued with the backend that won the facts merge, and stamp the same key on merged `/nodes` records.
- Emit all four fact keys including `environment`, which clients index directly.
- Skip injection for top-level `extract` queries, so `count()` and other aggregates keep the backends' own numbers, and for `/facts` queries constraining `name`; a `name` filter inside an `in` subquery still injects.
- Replace, never duplicate, an upstream fact of the configured name.
- Configure via `source_fact` / `source_fact_enabled` (`PDBMUX_SOURCE_FACT`, `PDBMUX_SOURCE_FACT_ENABLED`), defaulting to `pdbmux_source` enabled.
Reports are immutable history, so a node that migrated has reports in the
old PuppetDB and the new one; serve the union rather than picking a single
owning backend as /facts does.
Re-apply order_by/limit/offset over the merged set and sum X-Records, since
each backend only orders and pages its own slice.
Split out from node-lookup PR #17 into its own repo. pdbmux presents a
single merged PuppetDB v4 query surface over the old (Consul) and new
(k8s) PuppetDBs during the VM to k8s migration, and is deployed in-cluster
via argocd-apps as a container image.
unkin-agent
benvin