pdbmux is a small HTTP daemon that fronts two PuppetDB backends and serves a single, merged PuppetDB v4 query surface on one address. Point node-lookup, pblastreport, or anything else at pdbmux instead of a raw PuppetDB and it sees one consistent view spanning both.

Why

During the VM→k8s Puppet migration there are two PuppetDBs:

old — the legacy Consul-registered http://puppetdbapi.service.consul:8080
new — the k8s https://puppetdb.k8s.syd1.au.unkin.net (TLS terminated at the gateway; backends are plain PuppetDB on 8080)

Nodes move from old to new as they migrate, so at any moment a given node's current data lives in exactly one of them. pdbmux merges both so consumers don't have to know (or query twice) which PuppetDB a node currently lives in.

Endpoints

pdbmux proxies GET requests only. The query param (PuppetDB AST JSON, not PQL) is forwarded verbatim.

Path	Behaviour
`GET /pdb/query/v4/nodes`	Fan out to both backends, dedupe by `certname`, keep the record with the newer `report_timestamp`.
`GET /pdb/query/v4/facts`	Fan out to both, and per `certname` keep all facts from the backend that owns that node (see merge semantics).
`GET /pdb/query/v4/*` (any other)	Transparently proxied to the primary backend, unmerged, streamed verbatim.
`GET /healthz`	Per-backend reachability. `200 {"status":"ok"}` if all reachable, `200 degraded` if some fail, `503 down` if all fail.

Fan-out is concurrent. If one backend errors or times out, pdbmux serves the survivor's results and logs a warning; a merged endpoint only returns 502 when every backend fails. Response records are passed through as raw JSON so unknown fields survive untouched.

Merge semantics

/nodes — dedupe by certname; the record with the strictly-newer report_timestamp wins. On a tie (or when a node exists in only one backend), the preferred backend's record is kept.
/facts — node-level granularity. For a certname present in both backends, pdbmux keeps all of that node's facts from one backend and drops the other's, chosen by the merge strategy:
- freshness (default) — attribute each certname to whichever backend holds its newer report_timestamp. pdbmux derives this from a per-certname freshness map built by querying /nodes from both backends, cached for freshness_ttl (default 30s). Ties/fallbacks use prefer.
- static — always keep the prefer backend's facts for shared nodes. No extra /nodes query.
- A node present in only one backend always appears (falls back to whichever backend actually returned facts for it).

Config

Precedence (lowest → highest): defaults < config file < env vars (PDBMUX_*) < flags.

Config file: $XDG_CONFIG_HOME/pdbmux/config.yaml. In Kubernetes, configuration is supplied entirely via PDBMUX_* env vars (no config file), which is the supported deployment path — see Deployment.

# ~/.config/pdbmux/config.yaml  (local dev; in k8s use PDBMUX_* env instead)
listen: ":8080"
backends:
  - name: old
    url: http://puppetdbapi.service.consul:8080
  - name: new
    url: https://puppetdb.k8s.syd1.au.unkin.net
primary: new          # backend used for non-merged /pdb/query/v4/* pass-through
merge: freshness      # freshness | static
prefer: new           # winner on ties / static merge / fallback
timeout: 10s          # per-upstream request timeout
freshness_ttl: 30s    # freshness-map cache TTL (freshness merge only)

backends[*].url is a base URL (scheme://host[:port]), without the /pdb/query/v4/... path — pdbmux appends the path per request.

Env var	Overrides
`PDBMUX_LISTEN`	`listen`
`PDBMUX_PRIMARY`	`primary`
`PDBMUX_MERGE`	`merge`
`PDBMUX_PREFER`	`prefer`
`PDBMUX_TIMEOUT`	`timeout` (Go duration, e.g. `10s`)
`PDBMUX_FRESHNESS_TTL`	`freshness_ttl`
`PDBMUX_BACKENDS`	whole backend list, as `name=url,name=url`

Flags: --listen, --primary, --merge.

Running

pdbmux                 # start the proxy (serve is the default action)
pdbmux serve           # explicit
pdbmux config init     # write a default config file
pdbmux config show     # print active config after all overrides
pdbmux version

Point a consumer at it:

node-lookup --url http://localhost:8080/pdb/query/v4/facts -R
NODE_LOOKUP_URL=http://localhost:8080/pdb/query/v4/facts pblastreport somehost

Build

make build             # -> dist/pdbmux (CGO disabled, static)
make test              # go test -race ./...
make lint              # golangci-lint

Requires Go 1.25+. Dependencies: github.com/spf13/cobra (CLI), gopkg.in/yaml.v3 (config file).

Deployment

pdbmux runs in Kubernetes as a container, in line with the all-in-k8s estate direction — it is not shipped as a per-VM RPM/systemd service. The image is built and pushed on every v* tag (.woodpecker/docker.yaml) to:

artifactapi.k8s.syd1.au.unkin.net/docker-internal/pdbmux:<tag>

It is a minimal static (CGO_ENABLED=0) binary on a distroless base (Dockerfile), configured entirely via PDBMUX_* env vars, with a single HTTP listener and /healthz for liveness/readiness probes.

The Deployment/Service/Gateway manifests live in the estate's argocd-apps repo under apps/base/pdbmux/ (namespace pdbmux, 2 replicas), and it is exposed to VM/workstation node-lookup consumers over HTTPS at:

https://pdbmux.k8s.syd1.au.unkin.net

Locally you can still run the binary directly for development:

PDBMUX_BACKENDS='old=http://puppetdbapi.service.consul:8080,new=http://puppetdb.puppet.svc.cluster.local:8080' \
  pdbmux serve
curl -s localhost:8080/healthz

Version bumps

make patch             # tag vX.Y.(Z+1) and push (triggers the docker release)
make minor             # tag vX.(Y+1).0
make major             # tag v(X+1).0.0