Unanimity is the right rule for a fan-out of peers, but the per-certname
routes are not one: a backend that does not hold the certname answers 404
to say so, not to disagree, so requiring it to agree turned the owner's
real 500 into a 502 that described neither backend.
- Add askOrder, which says whether a set of backends was asked as peers
or owner-first, and resolve each round's replies under its own rule.
- Serve the first backend that answered on owner-routed paths, so an
unreachable owner still falls back rather than collapsing to 502.
- Keep unanimity for the merged, meta, metrics and pass-through routes.
- Cover the owner routes: owner errors against a non-owner 404, both
erroring differently, an unreachable owner, and a non-owner error
behind the owner's 200.
- Record what clientRefusal's 4xx exemption assumes about client certs.
openvoxdb does not reserve 5xx for its own faults: the same malformed
query is a 400 on /nodes and a 500 on /facts, and /metrics answers a flat
403, so a 4xx-only replay rule made pdbmux's behaviour depend on the
route. The meta and metrics handlers held their own copy of the gateway
error and bypassed the replay entirely.
- Replay any status from 400 up that every backend agreed on, with the
backend's own body and content type.
- Keep 502 for backends disagreeing on the status, or a backend that
answered nothing at all.
- Route /pdb/meta, /metrics and the pass-through path through the same
rule as the merged query handlers.
- Count a unanimous 5xx as a failed round and let it fall back to a stale
cache entry; only a unanimous 4xx stays exempt from both.
- Answer successful queries with openvoxdb's application/json;charset=utf-8.
## Why
Puppetboard 7.0.1 cannot run against pdbmux: it exits at import when
/pdb/meta/v1/version 404s, and its landing page, metrics and radiator views
404 on the Jolokia surface.
## How
- Serve /pdb/meta/v1/version, reporting the lowest version any backend runs,
and /pdb/meta/v1/server-time from the first reachable backend.
- Merge the Jolokia surface (/metrics/v2/read, /metrics/v2/list,
/metrics/v1/mbeans): objects union, numeric attributes sum by default, and
Min/Max/Uptime/StartTime plus the distribution stats take a bound or a mean.
- Route /nodes extract-count queries to the summing path ahead of the certname
merge, and give /resources aggregates the same path.
- Document the endpoints and merge semantics in the README.
- Cover version disagreement, metric rules, escaped MBean names, count summing
and the non-aggregate /nodes merge with httptest backends.
unkin-agent