Follow-up to backlog#1191 (optional sub-item). The main accept loop
spawned one task per socket with no global bound, so a connection flood
could exhaust file descriptors and memory and take existing traffic
down with it.
- New RUSTFS_API_MAX_CONNECTIONS (default 0 = unlimited, no semaphore
constructed, accept loop unchanged).
- When set, the loop acquires an owned semaphore permit BEFORE
accept(): at saturation it simply stops accepting and lets the
kernel backlog absorb bursts (TCP-native backpressure) instead of
accept-then-close churn. The permit moves into the connection task
and is released by RAII on any exit path, including TLS handshake
failures.
- Saturation is observable via the
rustfs_http_server_connection_cap_saturated_total counter, a
connection_cap_state startup event, and a per-wait debug event;
shutdown stays responsive while parked on the semaphore.
- The cap covers everything on the main listener (S3, admin, console,
internode gRPC); the constant docs carry sizing guidance.
- E2E coverage: ten sequential Connection-close requests against cap 2
prove permits never leak; two stalled connections saturating cap 2
leave a third unserved until their permits are released, after which
the queued request is accepted and answered.
Zhengchao An