A down backend costs a full timeout stall on every request, since fan-out
has no way to know before it asks, and the client is never told the answer
came from fewer backends than are configured.
- poll each backend's status endpoint in the background, one goroutine per
backend, with failure/success thresholds so a blip cannot flap it
- skip backends the prober has down, and fall open to querying all of them
when none is left healthy
- treat a not-yet-probed backend as healthy so a restart drops no traffic
- log only up/down transitions
- stamp merged responses with X-Backends: <contributed>/<configured>
- report per-backend probe state and the last round's partiality on /healthz
- add health_probe_enabled, health_probe_path, health_probe_interval,
health_probe_timeout, health_probe_failures and health_probe_successes,
with matching PDBMUX_* env vars and a --health-probe flag
A busy Puppetboard re-fans-out the same /facts query every few seconds, and a
502 is worse than 30-second-old facts when every PuppetDB is unreachable.
- Add a `Cache` interface (get reports fresh/stale/miss, put, stats) keyed on
`<path>?<params>` with keys and repeated values sorted, plus a no-op default
so uncached paths behave exactly as before.
- Route serveMerged/serveUnion/serveSummed through `serveCached`, so the
reports cache drops in at `cacheFor` without touching a handler.
- Back /facts and /nodes with a byte-bounded LRU: `facts_ttl` (default 30s,
clamped to a 30s cap) and `facts_cache_bytes` (default 64 MiB); expired
entries are kept and served only when every backend fails.
- Single-flight identical keys so N concurrent requests cause one fan-out.
- Surface `cache` state and `serving_stale` in /healthz and the cache settings
in `config show`.
## 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.
Remove hardcoded internal PuppetDB URLs and site-specific wording so the
project is publishable as-is.
- backends have no default; require config file or PDBMUX_BACKENDS
- primary/prefer default to the first configured backend
- config init writes example.com placeholders
- Load no longer validates, so config init/version work unconfigured
- genericise README, package doc, help text and Dockerfile comment
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