Hello, This series adds normal UDP-to-TCP fallback to HAProxy's DNS resolver. It follows the design RFC posted here:
https://www.mail-archive.com/[email protected]/msg47368.html An unprefixed IPv4, IPv6, or hostname nameserver now uses UDP first and retries a validated truncated response over TCP against the same address and port. Nameservers imported from resolv.conf use the same default. Explicit udp@, udp4@, udp6@, and dgram+ addresses remain UDP-only, while tcp@ remains TCP-only. TCP connections are established lazily and reuse the existing DNS stream connection pooling, pipelining, timeouts, and idle cleanup. Starting TCP fallback preserves the query ID and type and does not consume a resolver retry or trigger A/AAAA fallback. The accepted_payload_size setting remains the EDNS advertisement and UDP receive limit; TCP responses are accepted up to the DNS protocol maximum. Explicit UDP-only nameservers retain the existing handling of truncated SRV responses. The first two patches correct response-boundary parsing and stream idle-task scheduling. The cleanup then allows one logical nameserver to release both transports. The fourth patch implements the fallback behavior, configuration semantics, documentation, and tcp_fallback counter. The final patch adds the regression coverage. Thanks, Manu Manu Nicolas (5): BUG/MINOR: resolvers: accept fields at the response boundary BUG/MINOR: dns: schedule idle task after setting its thread CLEANUP: dns: centralize nameserver transport cleanup MEDIUM: resolvers: retry truncated UDP responses over TCP REGTEST: resolvers: cover UDP to TCP fallback addons/promex/README | 1 + doc/configuration.txt | 34 ++- include/haproxy/dns-t.h | 12 +- include/haproxy/dns.h | 5 +- include/haproxy/resolvers-t.h | 3 +- reg-tests/contrib/prometheus.vtc | 1 + reg-tests/resolvers/tcp_fallback.py | 152 +++++++++++++ reg-tests/resolvers/tcp_fallback.vtc | 136 ++++++++++++ src/dns.c | 45 ++-- src/resolvers.c | 313 +++++++++++++++++++-------- 10 files changed, 583 insertions(+), 119 deletions(-) create mode 100644 reg-tests/resolvers/tcp_fallback.py create mode 100644 reg-tests/resolvers/tcp_fallback.vtc base-commit: ff88d845a2646b6e34cccce12ff8e9fc80033795 -- 2.54.0
