A stale fallback is byte-identical to a fresh response, so a client has
no way to tell it is holding data pdbmux served only because every
backend was down; the sole signal is a log line and a /healthz counter.
Set X-Cache to hit, miss or stale and Age to whole seconds since the
served copy was stored on every response from a cached path. Neither
header is emitted by OpenVoxDB, so nothing upstream is shadowed.
A single flight is built by whichever request arrived first, but every
request on that key waits for it. Running the fan-out on the leader's
cancelable request context hands the leader's disconnect to followers
whose own connections are healthy: they get 502 all backends failed.
Waiters also parked on a WaitGroup, so a follower whose own client went
away stayed blocked until the leader finished.
Run the flight on a context detached from the leader's request and
bounded by the configured timeout, and pass that context into build so
the fan-out uses it. Give Do a context so a waiter can abandon a flight
it no longer needs; the leader ignores it and always runs fn to
completion, keeping the cache warm for the others. A caller that
abandons on its own cancellation writes no response.
- flightGroup.Do recovers a panicking fn so the leader and every waiter get a non-nil error instead of a zero-value success served as 200 []
- Note in the README that facts_cache_bytes budgets body bytes only
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`.
unkin-agent