* reverseproxy: reduce lock contention in dynamic SRV and A upstreams (#7946)
The shared SRV and A/AAAA caches held a global write lock across the DNS
lookup, so one slow or timing-out record blocked every unrelated
upstream source.
Lookups now run without the cache lock held, deduplicated per key with
singleflight. A per-key generation (stored on the cache entry, so it is
bounded by the cache cap) and a cache-wide epoch keep a lookup that was
in flight during ResetSRV/ResetAllSRV from writing its result back, and
are part of the singleflight key so callers after a reset do not join a
pre-reset lookup.
The shared lookup is detached from the request that started it and
bounded by its own 30s timeout; each caller still returns as soon as its
own context is done. Distinct lookups across both caches are capped by a
shared gate (64 running, 256 queued); beyond that they are shed, serving
a stale SRV entry if a grace period is set and one is cached.
SRV and A now share one cache implementation. AUpstreams also implements
CachingUpstreamSource (via new ResetA/ResetAllA), so retries purge its
cache entry like SRVUpstreams already did.
Rebased onto the move of this code into modules/internal/network (#7790,
#8252).
Fixes#7946
Co-authored-by: Francis Lavoie <lavofr@gmail.com>
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
* network: backdate cache entries in TestShedLookups instead of a 1ns refresh
On Windows two close time.Now() calls can report no elapsed time, so an
entry seeded with a 1ns refresh could still be fresh and skip the shed
path entirely.
* network: move the shared cache and lookup gate into cache.go
dynamicupstreams.go keeps the SRV/A API; the generic cache, its
singleflight/generation handling and the lookup gate are not specific to
either record type. No functional change.
* network: preserve cache reset and grace semantics
---------
Co-authored-by: Francis Lavoie <lavofr@gmail.com>
Co-authored-by: steadytao <mail@steadytao.com>
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