138 lines
6.7 KiB
Markdown
138 lines
6.7 KiB
Markdown
# pdbmux — merging PuppetDB proxy
|
|
|
|
`pdbmux` is a small HTTP daemon that fronts **several** PuppetDB backends and
|
|
serves a single, merged PuppetDB v4 query surface on one address. Point
|
|
Puppetboard, or any other PuppetDB API client, at `pdbmux` instead of a raw
|
|
PuppetDB and it sees one consistent view spanning all of them.
|
|
|
|
## Why
|
|
|
|
Running more than one PuppetDB — during a migration between two of them, or
|
|
across regions — means a given node's current data lives in exactly one at any
|
|
moment, and consumers have to know which, or query each in turn. `pdbmux`
|
|
merges them all so consumers don't have to know (or query twice) which PuppetDB
|
|
a node currently lives in.
|
|
|
|
All backends are equal — `pdbmux` is never told which one to favour. Backend
|
|
names are arbitrary labels and there is no fixed number of them. The configured
|
|
order is used only as a tie-break, so output is reproducible.
|
|
|
|
## 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 all backends, dedupe by `certname`, keep the record with the newer `report_timestamp`. |
|
|
| `GET /pdb/query/v4/facts` | Fan out to all, and per `certname` keep **all** facts from the backend that owns that node (see merge semantics). |
|
|
| `GET /pdb/query/v4/reports` | Fan out to all and serve the **union**, deduped by report `hash`, re-ordered and re-paged across backends. |
|
|
| `GET /pdb/query/v4/events` | Fan out to all and serve the **union**, deduped by record identity, re-ordered and re-paged. |
|
|
| `GET /pdb/query/v4/reports/<hash>/{events,logs,metrics}` | Ask every backend; serve the answer from whichever backend actually holds that report. `404` when none does. |
|
|
| `GET /pdb/query/v4/*` (any other) | No merge rule, so backends are tried in configured order and the first success is streamed back verbatim; if all reject it, the first upstream error response is replayed. |
|
|
| `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
|
|
surviving backends' 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, the backend listed first in `backends`
|
|
supplies the record — a tie-break only, so the merged output is deterministic.
|
|
- **`/facts`** — node-level granularity. For a `certname` present in more than
|
|
one backend, `pdbmux` keeps **all** of that node's facts from **one** backend and
|
|
drops the others', 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 every backend, cached for
|
|
`freshness_ttl` (default 30s).
|
|
- **`static`** — skip the extra `/nodes` query and take each shared node's
|
|
facts from the first backend in configured order that holds it.
|
|
- A node present in only one backend always appears (falls back to whichever
|
|
backend actually returned facts for it).
|
|
- **`/reports`, `/events`** — **union**, not a per-node winner. Reports are
|
|
immutable history, so a node's reports can legitimately exist in more than one
|
|
backend and all of them belong in the merged view. Reports dedupe on `hash`;
|
|
events, which carry no id of their own, dedupe on the verbatim record (a node
|
|
reporting to more than one backend stores identical records in each). Records
|
|
the merge cannot key — `extract`/`group_by` aggregate rows — are never
|
|
deduped, so every backend's rows pass through even when byte-identical;
|
|
summing those aggregates across backends is not implemented yet.
|
|
|
|
### Paging and ordering on the merged endpoints
|
|
|
|
Each backend applies `order_by`/`limit`/`offset` to its own slice only, so
|
|
`pdbmux` re-does all three over the union:
|
|
|
|
- `order_by` is parsed and the merged set re-sorted by those fields (ties keep
|
|
the merged set's existing order). A record missing an ordered field sorts first.
|
|
- Backends are asked for the first `offset + limit` records — never an `offset`
|
|
— and the requested window is then cut from the merged, re-sorted set.
|
|
- `include_total=true` makes `pdbmux` sum each backend's `X-Records` header into
|
|
one merged header. Deduped records are counted once per backend, so the total
|
|
is an upper bound.
|
|
- A malformed `limit`, `offset` or `order_by` gets a `400` rather than being
|
|
forwarded.
|
|
|
|
## Config
|
|
|
|
Precedence (lowest → highest): **defaults < config file < env vars (`PDBMUX_*`) < flags**.
|
|
|
|
Config file: `$XDG_CONFIG_HOME/pdbmux/config.yaml`. In a container there is no
|
|
config file — everything comes from `PDBMUX_*` env vars.
|
|
|
|
```yaml
|
|
listen: ":8080"
|
|
backends: # order is a tie-break only, not a ranking
|
|
- name: pdb-a
|
|
url: http://puppetdb1.example.com:8080
|
|
- name: pdb-b
|
|
url: https://puppetdb2.example.com
|
|
merge: freshness # freshness | static
|
|
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]`); `pdbmux` appends
|
|
the `/pdb/query/v4/...` path per request.
|
|
|
|
| Env var | Overrides |
|
|
|---|---|
|
|
| `PDBMUX_LISTEN` | `listen` |
|
|
| `PDBMUX_MERGE` | `merge` |
|
|
| `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`, `--merge`.
|
|
|
|
## Running
|
|
|
|
Subcommands: `serve` (default), `config init`, `config show`, `version`. Run
|
|
`pdbmux --help` for details. Any PuppetDB v4 client works against the `pdbmux`
|
|
base URL in place of a PuppetDB one.
|
|
|
|
```bash
|
|
PDBMUX_BACKENDS='pdb-a=http://puppetdb1.example.com:8080,pdb-b=http://puppetdb2.example.com:8080' pdbmux
|
|
curl -s --get http://localhost:8080/pdb/query/v4/nodes \
|
|
--data-urlencode 'query=["=","certname","host1.example.com"]'
|
|
```
|
|
|
|
## Build
|
|
|
|
`make build` (static binary into `dist/`), `make test`, `make lint`. Requires Go 1.25+.
|
|
|
|
## Deployment
|
|
|
|
Container image only — no OS package. Every `v*` tag builds and pushes the image
|
|
(`.woodpecker/docker.yaml`); registry and repository are pipeline settings. Tag
|
|
with `make patch` / `minor` / `major`.
|
|
|
|
A static (`CGO_ENABLED=0`) binary on a distroless base, configured entirely via
|
|
`PDBMUX_*` env vars; a container needs at minimum `PDBMUX_BACKENDS`. Stateless,
|
|
so run as many replicas as you like; use `/healthz` for liveness/readiness
|
|
probes.
|