QUIC restarts, slow problems: udpgrm to the rescue

Cloudflare introduces udpgrm, a lightweight daemon that enables zero-downtime restarts for UDP servers by leveraging Linux SO_REUSEPORT and eBPF to keep flows sticky across socket generations. The post explains how udpgrm manages flow routing via configurable dissectors (FLOW, CBPF, NOOP, BESPOKE with QUIC examples), integrates through cgroup hooks and a setsockopt/getsockopt API, and supports systemd workflows with udpgrm_activate.py for socket activation and a decoy process to maintain concurrent instances during upgrades.