并发测试的时候发现nginx 502 bad gateway 了,看了下日志发现很多upstream Cannot assign requested address的记录
connect() to 192.168.89.170:80 failed (99: Cannot assign requested address) while connecting to upstream

正常判断应该是端口不够用了
不过,我确实开启了: net.ipv4.tcp_tw_recycle = 1 和 net.ipv4.tcp_tw_reuse = 1两个参数
理论上应该可以把timewait 端口重用,查了下这个参数跟tcp_timestamps有关(http://blog.sina.com.cn/s/blog_781b0c850100znjd.html)

if (tmp_opt.saw_tstamp &&
tcp_death_row.sysctl_tw_recycle &&
(dst = inet_csk_route_req(sk, req)) != NULL &&
(peer = rt_get_peer((struct rtable *)dst)) != NULL &&
peer->v4daddr == saddr) {
if (get_seconds() < peer->tcp_ts_stamp + TCP_PAWS_MSL &&
(s32)(peer->tcp_ts – req->ts_recent) >
TCP_PAWS_WINDOW) {
NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_PAWSPASSIVEREJECTED);
goto drop_and_release;
}
}

tmp_opt.saw_tstamp：该socket支持tcp_timestamp
sysctl_tw_recycle：本机系统开启tcp_tw_recycle选项
TCP_PAWS_MSL：60s，该条件判断表示该源ip的上次tcp通讯发生在60s内
TCP_PAWS_WINDOW：1，该条件判断表示该源ip的上次tcp通讯的timestamp 大于 本次tcp

因此: 应该在proxy端和后端都开启net.ipv4.tcp_timestamps=1